erl_nif

A NIF library contains native implementation of some functions of an Erlang module. The native implemented functions (NIFs) are called like any other functions without any difference to the caller. Each NIF must have an implementation in Erlang that is invoked if the function is called before the NIF library is successfully loaded. A typical such stub implementation is to throw an exception. But it can also be used as a fallback implementation if the NIF library is not implemented for some architecture.

A minimal example of a NIF library can look as follows:

/* niftest.c */
#include "erl_nif.h"

static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
    return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1);
}

static ErlNifFunc nif_funcs[] =
{
    {"hello", 0, hello}
};

ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)

The Erlang module can look as follows:

-module(niftest).

-export([init/0, hello/0]).

init() ->
      erlang:load_nif("./niftest", 0).

hello() ->
      "NIF library not loaded".

Compile and test can look as follows (on Linux):

$> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
$> erl

1> c(niftest).
{ok,niftest}
2> niftest:hello().
"NIF library not loaded"
3> niftest:init().
ok
4> niftest:hello().
"Hello world!"

A better solution for a real module is to take advantage of the new directive on load (see section Running a Function When a Module is Loaded in the Erlang Reference Manual) to load the NIF library automatically when the module is loaded.

A loaded NIF library is tied to the Erlang module code version that loaded it. If the module is upgraded with a new version, the new Erlang code need to load its own NIF library (or maybe choose not to). The new code version can, however, choose to load the same NIF library as the old code if it wants to. Sharing the dynamic library means that static data defined by the library is shared as well. To avoid unintentionally shared static data, each Erlang module code can keep its own private data. This private data can be set when the NIF library is loaded and then retrieved by calling enif_priv_data.

A NIF library cannot be loaded explicitly. A library is automatically unloaded when the module code that it belongs to is purged by the code server.

All functions that a NIF library needs to do with Erlang are performed through the NIF API functions. Functions exist for the following functionality:

Read and write Erlang terms

Any Erlang terms can be passed to a NIF as function arguments and be returned as function return values. The terms are of C-type ERL_NIF_TERM and can only be read or written using API functions. Most functions to read the content of a term are prefixed enif_get_ and usually return true (or false) if the term is of the expected type (or not). The functions to write terms are all prefixed enif_make_ and usually return the created ERL_NIF_TERM. There are also some functions to query terms, like enif_is_atom, enif_is_identical, and enif_compare.

All terms of type ERL_NIF_TERM belong to an environment of type ErlNifEnv. The lifetime of a term is controlled by the lifetime of its environment object. All API functions that read or write terms has the environment that the term belongs to as the first function argument.

Binaries

Terms of type binary are accessed with the help of struct type ErlNifBinary, which contains a pointer (data) to the raw binary data and the length (size) of the data in bytes. Both data and size are read-only and are only to be written using calls to API functions. Instances of ErlNifBinary are, however, always allocated by the user (usually as local variables).

The raw data pointed to by data is only mutable after a call to enif_alloc_binary or enif_realloc_binary. All other functions that operate on a binary leave the data as read-only. A mutable binary must in the end either be freed with enif_release_binary or made read-only by transferring it to an Erlang term with enif_make_binary. However, it does not have to occur in the same NIF call. Read-only binaries do not have to be released.

enif_make_new_binary can be used as a shortcut to allocate and return a binary in the same NIF call.

Binaries are sequences of whole bytes. Bitstrings with an arbitrary bit length have no support yet.

Resource objects

The use of resource objects is a safe way to return pointers to native data structures from a NIF. A resource object is only a block of memory allocated with enif_alloc_resource. A handle ("safe pointer") to this memory block can then be returned to Erlang by the use of enif_make_resource. The term returned by enif_make_resource is opaque in nature. It can be stored and passed between processes on the same node, but the only real end usage is to pass it back as an argument to a NIF. The NIF can then call enif_get_resource and get back a pointer to the memory block, which is guaranteed to still be valid. A resource object is not deallocated until the last handle term is garbage collected by the VM and the resource is released with enif_release_resource (not necessarily in that order).

All resource objects are created as instances of some resource type. This makes resources from different modules to be distinguishable. A resource type is created by calling enif_open_resource_type when a library is loaded. Objects of that resource type can then later be allocated and enif_get_resource verifies that the resource is of the expected type. A resource type can have a user-supplied destructor function, which is automatically called when resources of that type are released (by either the garbage collector or enif_release_resource). Resource types are uniquely identified by a supplied name string and the name of the implementing module.

The following is a template example of how to create and return a resource object.

ERL_NIF_TERM term;
MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct));

/* initialize struct ... */

term = enif_make_resource(env, obj);

if (keep_a_reference_of_our_own) {
    /* store 'obj' in static variable, private data or other resource object */
}
else {
    enif_release_resource(obj);
    /* resource now only owned by "Erlang" */
}
return term;

Notice that once enif_make_resource creates the term to return to Erlang, the code can choose to either keep its own native pointer to the allocated struct and release it later, or release it immediately and rely only on the garbage collector to deallocate the resource object eventually when it collects the term.

Another use of resource objects is to create binary terms with user-defined memory management. enif_make_resource_binary creates a binary term that is connected to a resource object. The destructor of the resource is called when the binary is garbage collected, at which time the binary data can be released. An example of this can be a binary term consisting of data from a mmap'ed file. The destructor can then do munmap to release the memory region.

Resource types support upgrade in runtime by allowing a loaded NIF library to take over an already existing resource type and by that "inherit" all existing objects of that type. The destructor of the new library is thereafter called for the inherited objects and the library with the old destructor function can be safely unloaded. Existing resource objects, of a module that is upgraded, must either be deleted or taken over by the new NIF library. The unloading of a library is postponed as long as there exist resource objects with a destructor function in the library.

Threads and concurrency

A NIF is thread-safe without any explicit synchronization as long as it acts as a pure function and only reads the supplied arguments. When you write to a shared state either through static variables or enif_priv_data, you need to supply your own explicit synchronization. This includes terms in process-independent environments that are shared between threads. Resource objects also require synchronization if you treat them as mutable.

The library initialization callbacks load, reload, and upgrade are all thread-safe even for shared state data.

Version Management

When a NIF library is built, information about the NIF API version is compiled into the library. When a NIF library is loaded, the runtime system verifies that the library is of a compatible version. erl_nif.h defines the following:

ERL_NIF_MAJOR_VERSION

Incremented when NIF library incompatible changes are made to the Erlang runtime system. Normally it suffices to recompile the NIF library when the ERL_NIF_MAJOR_VERSION has changed, but it can, under rare circumstances, mean that NIF libraries must be slightly modified. If so, this will of course be documented.

ERL_NIF_MINOR_VERSION

Incremented when new features are added. The runtime system uses the minor version to determine what features to use.

The runtime system normally refuses to load a NIF library if the major versions differ, or if the major versions are equal and the minor version used by the NIF library is greater than the one used by the runtime system. Old NIF libraries with lower major versions are, however, allowed after a bump of the major version during a transition period of two major releases. Such old NIF libraries can however fail if deprecated features are used.

Time Measurement

Support for time measurement in NIF libraries:

• ErlNifTime
• ErlNifTimeUnit
• enif_monotonic_time()
• enif_time_offset()
• enif_convert_time_unit()

Long-running NIFs

As mentioned in the warning text at the beginning of this manual page, it is of vital importance that a native function returns relatively fast. It is difficult to give an exact maximum amount of time that a native function is allowed to work, but usually a well-behaving native function is to return to its caller within 1 millisecond. This can be achieved using different approaches. If you have full control over the code to execute in the native function, the best approach is to divide the work into multiple chunks of work and call the native function multiple times. This is, however, not always possible, for example when calling third-party libraries.

The enif_consume_timeslice() function can be used to inform the runtime system about the length of the NIF call. It is typically always to be used unless the NIF executes very fast.

If the NIF call is too lengthy, this must be handled in one of the following ways to avoid degraded responsiveness, scheduler load balancing problems, and other strange behaviors:

Yielding NIF

If the functionality of a long-running NIF can be split so that its work can be achieved through a series of shorter NIF calls, the application has two options:

• Make that series of NIF calls from the Erlang level.

• Call a NIF that first performs a chunk of the work, then invokes the enif_schedule_nif function to schedule another NIF call to perform the next chunk. The final call scheduled in this manner can then return the overall result.

Breaking up a long-running function in this manner enables the VM to regain control between calls to the NIFs.

This approach is always preferred over the other alternatives described below. This both from a performance perspective and a system characteristics perspective.

Threaded NIF

This is accomplished by dispatching the work to another thread managed by the NIF library, return from the NIF, and wait for the result. The thread can send the result back to the Erlang process using enif_send. Information about thread primitives is provided below.

Dirty NIF

Note

The dirty NIF functionality described here is experimental. Dirty NIF support is available only when the emulator is configured with dirty schedulers enabled. This feature is disabled by default. The Erlang runtime without SMP support does not support dirty schedulers even when the dirty scheduler support is enabled. To check at runtime for the presence of dirty scheduler threads, code can use the enif_system_info() API function.

A NIF that cannot be split and cannot execute in a millisecond or less is called a "dirty NIF", as it performs work that the ordinary schedulers of the Erlang runtime system cannot handle cleanly. Applications that make use of such functions must indicate to the runtime that the functions are dirty so they can be handled specially. This is handled by executing dirty jobs on a separate set of schedulers called dirty schedulers. A dirty NIF executing on a dirty scheduler does not have the same duration restriction as a normal NIF.

It is important to classify the dirty job correct. An I/O bound job should be classified as such, and a CPU bound job should be classified as such. If you should classify CPU bound jobs as I/O bound jobs, dirty I/O schedulers might starve ordinary schedulers. I/O bound jobs are expected to either block waiting for I/O, and/or spend a limited amount of time moving data.

To schedule a dirty NIF for execution, the application has two options:

• Set the appropriate flags value for the dirty NIF in its ErlNifFunc entry.

• Call enif_schedule_nif, pass to it a pointer to the dirty NIF to be executed, and indicate with argument flags whether it expects the operation to be CPU-bound or I/O-bound.

A job that alternates between I/O bound and CPU bound can be reclassified and rescheduled using enif_schedule_nif so that it executes on the correct type of dirty scheduler at all times. For more information see the documentation of the erl(1) command line arguments +SDcpu, and +SDio.

While a process executes a dirty NIF, some operations that communicate with it can take a very long time to complete. Suspend or garbage collection of a process executing a dirty NIF cannot be done until the dirty NIF has returned. Thus, other processes waiting for such operations to complete might have to wait for a very long time. Blocking multi-scheduling, that is, calling erlang:system_flag(multi_scheduling, block), can also take a very long time to complete. This becaue all ongoing dirty operations on all dirty schedulers must complete before the block operation can complete.

Many operations communicating with a process executing a dirty NIF can, however, complete while it executes the dirty NIF. For example, retrieving information about it through erlang:process_info, setting its group leader, register/unregister its name, and so on.

Termination of a process executing a dirty NIF can only be completed up to a certain point while it executes the dirty NIF. All Erlang resources, such as its registered name and its ETS tables, are released. All links and monitors are triggered. The execution of the NIF is, however, not stopped. The NIF can safely continue execution, allocate heap memory, and so on, but it is of course better to stop executing as soon as possible. The NIF can check whether a current process is alive using enif_is_current_process_alive. Communication using enif_send and enif_port_command is also dropped when the sending process is not alive. Deallocation of certain internal resources, such as process heap and process control block, is delayed until the dirty NIF has completed.

ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, reload, upgrade, unload)

This is the magic macro to initialize a NIF library. It is to be evaluated in global file scope.

MODULE is the name of the Erlang module as an identifier without string quotations. It is stringified by the macro.

funcs is a static array of function descriptors for all the implemented NIFs in this library.

load, reload, upgrade and unload are pointers to functions. One of load, reload, or upgrade is called to initialize the library. unload is called to release the library. All are described individually below.

If compiling a NIF for static inclusion through --enable-static-nifs, you must define STATIC_ERLANG_NIF before the ERL_NIF_INIT declaration.

int (*load)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)

load is called when the NIF library is loaded and no previously loaded library exists for this module.

*priv_data can be set to point to some private data that the library needs to keep a state between NIF calls. enif_priv_data returns this pointer. *priv_data is initialized to NULL when load is called.

load_info is the second argument to erlang:load_nif/2.

The library fails to load if load returns anything other than 0. load can be NULL if initialization is not needed.

int (*upgrade)(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info)

upgrade is called when the NIF library is loaded and there is old code of this module with a loaded NIF library.

Works as load, except that *old_priv_data already contains the value set by the last call to load or reload for the old module code. *priv_data is initialized to NULL when upgrade is called. It is allowed to write to both *priv_data and *old_priv_data.

The library fails to load if upgrade returns anything other than 0 or if upgrade is NULL.

void (*unload)(ErlNifEnv* env, void* priv_data)

unload is called when the module code that the NIF library belongs to is purged as old. New code of the same module may or may not exist. Notice that unload is not called for a replaced library as a consequence of reload.

int (*reload)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)

Note

The reload mechanism is deprecated. It was only intended as a development feature. Do not use it as an upgrade method for live production systems. It can be removed in future releases. Ensure to pass reload as NULL to ERL_NIF_INIT to disable it when not used.

reload is called when the NIF library is loaded and a previously loaded library already exists for this module code.

Works as load, except that *priv_data already contains the value set by the previous call to load or reload.

The library fails to load if reload returns anything other than 0 or if reload is NULL.

ERL_NIF_TERM

Variables of type ERL_NIF_TERM can refer to any Erlang term. This is an opaque type and values of it can only by used either as arguments to API functions or as return values from NIFs. All ERL_NIF_TERMs belong to an environment (ErlNifEnv). A term cannot be destructed individually, it is valid until its environment is destructed.

ErlNifEnv

ErlNifEnv represents an environment that can host Erlang terms. All terms in an environment are valid as long as the environment is valid. ErlNifEnv is an opaque type; pointers to it can only be passed on to API functions. Two types of environments exist:

Process-bound environment

Passed as the first argument to all NIFs. All function arguments passed to a NIF belong to that environment. The return value from a NIF must also be a term belonging to the same environment.

A process-bound environment contains transient information about the calling Erlang process. The environment is only valid in the thread where it was supplied as argument until the NIF returns. It is thus useless and dangerous to store pointers to process-bound environments between NIF calls.

Process-independent environment

Created by calling enif_alloc_env. This environment can be used to store terms between NIF calls and to send terms with enif_send. A process-independent environment with all its terms is valid until you explicitly invalidate it with enif_free_env or enif_send.

All contained terms of a list/tuple/map must belong to the same environment as the list/tuple/map itself. Terms can be copied between environments with enif_make_copy.

ErlNifFunc

typedef struct {
    const char* name;
    unsigned arity;
    ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
    unsigned flags;
} ErlNifFunc;

Describes a NIF by its name, arity, and implementation.

fptr

A pointer to the function that implements the NIF.

argv

Contains the function arguments passed to the NIF.

argc

The array length, that is, the function arity. argv[N-1] thus denotes the Nth argument to the NIF. Notice that the argument argc allows for the same C function to implement several Erlang functions with different arity (but probably with the same name).

flags

Is 0 for a regular NIF (and so its value can be omitted for statically initialized ErlNifFunc instances).

flags can be used to indicate that the NIF is a dirty NIF that is to be executed on a dirty scheduler thread.

The dirty NIF functionality described here is experimental. You have to enable support for dirty schedulers when building OTP to try out the functionality.

If the dirty NIF is expected to be CPU-bound, its flags field is to be set to ERL_NIF_DIRTY_JOB_CPU_BOUND or ERL_NIF_DIRTY_JOB_IO_BOUND.

Note

If one of the ERL_NIF_DIRTY_JOB_*_BOUND flags is set, and the runtime system has no support for dirty schedulers, the runtime system refuses to load the NIF library.

ErlNifBinary

typedef struct {
    unsigned size;
    unsigned char* data;
} ErlNifBinary;

ErlNifBinary contains transient information about an inspected binary term. data is a pointer to a buffer of size bytes with the raw content of the binary.

Notice that ErlNifBinary is a semi-opaque type and you are only allowed to read fields size and data.

ErlNifBinaryToTerm

An enumeration of the options that can be specified to enif_binary_to_term. For default behavior, use value 0.

When receiving data from untrusted sources, use option ERL_NIF_BIN2TERM_SAFE.

ErlNifPid

A process identifier (pid). In contrast to pid terms (instances of ERL_NIF_TERM), ErlNifPids are self-contained and not bound to any environment. ErlNifPid is an opaque type.

ErlNifPort

A port identifier. In contrast to port ID terms (instances of ERL_NIF_TERM), ErlNifPorts are self-contained and not bound to any environment. ErlNifPort is an opaque type.

ErlNifResourceType

Each instance of ErlNifResourceType represents a class of memory-managed resource objects that can be garbage collected. Each resource type has a unique name and a destructor function that is called when objects of its type are released.

ErlNifResourceDtor

typedef void ErlNifResourceDtor(ErlNifEnv* env, void* obj);

The function prototype of a resource destructor function.

ErlNifCharEncoding

typedef enum {
    ERL_NIF_LATIN1
}ErlNifCharEncoding;

The character encoding used in strings and atoms. The only supported encoding is ERL_NIF_LATIN1 for ISO Latin-1 (8-bit ASCII).

ErlNifSysInfo

Used by enif_system_info to return information about the runtime system. Contains the same content as ErlDrvSysInfo.

ErlNifSInt64

A native signed 64-bit integer type.

ErlNifUInt64

A native unsigned 64-bit integer type.

ErlNifTime

A signed 64-bit integer type for representation of time.

ErlNifTimeUnit

An enumeration of time units supported by the NIF API:

ERL_NIF_SEC

Seconds

ERL_NIF_MSEC

Milliseconds

ERL_NIF_USEC

Microseconds

ERL_NIF_NSEC

Nanoseconds

ErlNifUniqueInteger

An enumeration of the properties that can be requested from enif_unique_integer. For default properties, use value 0.

ERL_NIF_UNIQUE_POSITIVE

Return only positive integers.

ERL_NIF_UNIQUE_MONOTONIC

Return only strictly monotonically increasing integer corresponding to creation time.

Allocates memory of size bytes.

Returns NULL if the allocation fails.

Allocates a new binary of size size bytes. Initializes the structure pointed to by bin to refer to the allocated binary. The binary must either be released by enif_release_binary or ownership transferred to an Erlang term with enif_make_binary. An allocated (and owned) ErlNifBinary can be kept between NIF calls.

Returns true on success, or false if allocation fails.

Allocates a new process-independent environment. The environment can be used to hold terms that are not bound to any process. Such terms can later be copied to a process environment with enif_make_copy or be sent to a process as a message with enif_send.

Returns pointer to the new environment.

Allocates a memory-managed resource object of type type and size size bytes.

Creates a term that is the result of decoding the binary data at data, which must be encoded according to the Erlang external term format. No more than size bytes are read from data. Argument opts corresponds to the second argument to erlang:binary_to_term/2 and must be either 0 or ERL_NIF_BIN2TERM_SAFE.

On success, stores the resulting term at *term and returns the number of bytes read. Returns 0 if decoding fails or if opts is invalid.

See also ErlNifBinaryToTerm, erlang:binary_to_term/2, and enif_term_to_binary.

Frees all terms in an environment and clears it for reuse. The environment must have been allocated with enif_alloc_env.

Returns an integer < 0 if lhs < rhs, 0 if lhs = rhs, and > 0 if lhs > rhs. Corresponds to the Erlang operators ==, /=, =<, <, >=, and > (but not =:= or =/=).

Same as erl_drv_cond_broadcast.

Same as erl_drv_cond_create.

Same as erl_drv_cond_destroy.

Same as erl_drv_cond_signal.

Same as erl_drv_cond_wait.

Gives the runtime system a hint about how much CPU time the current NIF call has consumed since the last hint, or since the start of the NIF if no previous hint has been specified. The time is specified as a percent of the timeslice that a process is allowed to execute Erlang code until it can be suspended to give time for other runnable processes. The scheduling timeslice is not an exact entity, but can usually be approximated to about 1 millisecond.

Notice that it is up to the runtime system to determine if and how to use this information. Implementations on some platforms can use other means to determine consumed CPU time. Lengthy NIFs should regardless of this frequently call enif_consume_timeslice to determine if it is allowed to continue execution.

Argument percent must be an integer between 1 and 100. This function must only be called from a NIF-calling thread, and argument env must be the environment of the calling process.

Returns 1 if the timeslice is exhausted, otherwise 0. If 1 is returned, the NIF is to return as soon as possible in order for the process to yield.

This function is provided to better support co-operative scheduling, improve system responsiveness, and make it easier to prevent misbehaviors of the VM because of a NIF monopolizing a scheduler thread. It can be used to divide length work into a number of repeated NIF calls without the need to create threads.

See also the warning text at the beginning of this manual page.

Converts the val value of time unit from to the corresponding value of time unit to. The result is rounded using the floor function.

val

Value to convert time unit for.

from

Time unit of val.

to

Time unit of returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument.

See also ErlNifTime and ErlNifTimeUnit.

Returns the CPU time in the same format as erlang:timestamp(). The CPU time is the time the current logical CPU has spent executing since some arbitrary point in the past. If the OS does not support fetching this value, enif_cpu_time invokes enif_make_badarg.

Same as erl_drv_equal_tids.

Frees memory allocated by enif_alloc.

Frees an environment allocated with enif_alloc_env. All terms created in the environment are freed as well.

Writes a NULL-terminated string in the buffer pointed to by buf of size size, consisting of the string representation of the atom term with encoding encode.

Returns the number of bytes written (including terminating NULL character) or 0 if term is not an atom with maximum length of size-1.

Sets *len to the length (number of bytes excluding terminating NULL character) of the atom term with encoding encode.

Returns true on success, or false if term is not an atom.

Sets *dp to the floating-point value of term.

Returns true on success, or false if term is not a float.

Sets *ip to the integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of type int.

Sets *ip to the integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of a signed 64-bit integer.

If term is the pid of a node local process, this function initializes the pid variable *pid from it and returns true. Otherwise returns false. No check is done to see if the process is alive.

If term identifies a node local port, this function initializes the port variable *port_id from it and returns true. Otherwise returns false. No check is done to see if the port is alive.

Sets *head and *tail from list list.

Returns true on success, or false if it is not a list or the list is empty.

Sets *len to the length of list term.

Returns true on success, or false if term is not a proper list.

Sets *ip to the long integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of type long int.

Sets *size to the number of key-value pairs in the map term.

Returns true on success, or false if term is not a map.

Sets *value to the value associated with key in the map map.

Returns true on success, or false if map is not a map or if map does not contain key.

Sets *objp to point to the resource object referred to by term.

Returns true on success, or false if term is not a handle to a resource object of type type.

Writes a NULL-terminated string in the buffer pointed to by buf with size size, consisting of the characters in the string list. The characters are written using encoding encode.

Returns one of the following:

• The number of bytes written (including terminating NULL character)
• -size if the string was truncated because of buffer space
• 0 if list is not a string that can be encoded with encode or if size was < 1.

The written string is always NULL-terminated, unless buffer size is < 1.

If term is a tuple, this function sets *array to point to an array containing the elements of the tuple, and sets *arity to the number of elements. Notice that the array is read-only and (*array)[N-1] is the Nth element of the tuple. *array is undefined if the arity of the tuple is zero.

Returns true on success, or false if term is not a tuple.

Sets *ip to the unsigned integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of type unsigned int.

Sets *ip to the unsigned integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of an unsigned 64-bit integer.

Sets *ip to the unsigned long integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of type unsigned long.

Same as erl_drv_getenv.

Returns true if a pending exception is associated with the environment env. If reason is a NULL pointer, ignore it. Otherwise, if a pending exception associated with env exists, set ERL_NIF_TERM to which reason points to the value of the exception's term. For example, if enif_make_badarg is called to set a pending badarg exception, a later call to enif_has_pending_exception(env, &reason) sets reason to the atom badarg, then return true.

See also enif_make_badarg and enif_raise_exception.

Initializes the structure pointed to by bin with information about binary term bin_term.

Returns true on success, or false if bin_term is not a binary.

Initializes the structure pointed to by bin with a continuous buffer with the same byte content as iolist. As with inspect_binary, the data pointed to by bin is transient and does not need to be released.

Returns true on success, or false if iolist is not an iolist.

Returns true if term is an atom.

Returns true if term is a binary.

Returns true if the currently executing process is currently alive, otherwise false.

This function can only be used from a NIF-calling thread, and with an environment corresponding to currently executing processes.

Returns true if term is an empty list.

Return true if term is an exception.

Returns true if term is a fun.

Returns true if the two terms are identical. Corresponds to the Erlang operators =:= and =/=.

Returns true if term is a list.

Returns true if term is a map, otherwise false.

Returns true if term is a number.

Returns true if term is a pid.

Returns true if term is a port.

Returns true if port_id is alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Returns true if pid is alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Returns true if term is a reference.

Returns true if term is a tuple.

Adds a reference to resource object obj obtained from enif_alloc_resource. Each call to enif_keep_resource for an object must be balanced by a call to enif_release_resource before the object is destructed.

Creates an atom term from the NULL-terminated C-string name with ISO Latin-1 encoding. If the length of name exceeds the maximum length allowed for an atom (255 characters), enif_make_atom invokes enif_make_badarg.

Create an atom term from the string name with length len. NULL characters are treated as any other characters. If len exceeds the maximum length allowed for an atom (255 characters), enif_make_atom invokes enif_make_badarg.

Makes a badarg exception to be returned from a NIF, and associates it with environment env. Once a NIF or any function it calls invokes enif_make_badarg, the runtime ensures that a badarg exception is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.

The return value from enif_make_badarg can be used only as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception, but not to any other NIF API function.

See also enif_has_pending_exception and enif_raise_exception.

Makes a binary term from bin. Any ownership of the binary data is transferred to the created term and bin is to be considered read-only for the rest of the NIF call and then as released.

Makes a copy of term src_term. The copy is created in environment dst_env. The source term can be located in any environment.

Creates a floating-point term from a double. If argument double is not finite or is NaN, enif_make_double invokes enif_make_badarg.

Tries to create the term of an already existing atom from the NULL-terminated C-string name with encoding encode.

If the atom already exists, this function stores the term in *atom and returns true, otherwise false. Also returns false if the length of name exceeds the maximum length allowed for an atom (255 characters).

Tries to create the term of an already existing atom from the string name with length len and encoding encode. NULL characters are treated as any other characters.

If the atom already exists, this function stores the term in *atom and returns true, otherwise false. Also returns false if len exceeds the maximum length allowed for an atom (255 characters).

Creates an integer term.

Creates an integer term from a signed 64-bit integer.

Creates an ordinary list term of length cnt. Expects cnt number of arguments (after cnt) of type ERL_NIF_TERM as the elements of the list.

Returns an empty list if cnt is 0.

Creates an ordinary list term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_list to get a compile-time error if the number of arguments does not match.

Creates a list cell [head | tail].

Creates an ordinary list containing the elements of array arr of length cnt.

Returns an empty list if cnt is 0.

Creates an integer term from a long int.

Makes a copy of map map_in and inserts key with value. If key already exists in map_in, the old associated value is replaced by value.

If successful, this function sets *map_out to the new map and returns true. Returns false if map_in is not a map.

The map_in term must belong to environment env.

If map map_in contains key, this function makes a copy of map_in in *map_out, and removes key and the associated value. If map map_in does not contain key, *map_out is set to map_in.

Returns true on success, or false if map_in is not a map.

The map_in term must belong to environment env.

Makes a copy of map map_in and replace the old associated value for key with new_value.

If successful, this function sets *map_out to the new map and returns true. Returns false if map_in is not a map or if it does not contain key.

The map_in term must belong to environment env.

Allocates a binary of size size bytes and creates an owning term. The binary data is mutable until the calling NIF returns. This is a quick way to create a new binary without having to use ErlNifBinary. The drawbacks are that the binary cannot be kept between NIF calls and it cannot be reallocated.

Returns a pointer to the raw binary data and sets *termp to the binary term.

Makes an empty map term.

Makes a pid term from *pid.

Creates a reference like erlang:make_ref/0.

Creates an opaque handle to a memory-managed resource object obtained by enif_alloc_resource. No ownership transfer is done, as the resource object still needs to be released by enif_release_resource. However, notice that the call to enif_release_resource can occur immediately after obtaining the term from enif_make_resource, in which case the resource object is deallocated when the term is garbage collected. For more details, see the example of creating and returning a resource object in the User's Guide.

Notice that the only defined behavior of using a resource term in an Erlang program is to store it and send it between processes on the same node. Other operations, such as matching or term_to_binary, have unpredictable (but harmless) results.

Creates a binary term that is memory-managed by a resource object obj obtained by enif_alloc_resource. The returned binary term consists of size bytes pointed to by data. This raw binary data must be kept readable and unchanged until the destructor of the resource is called. The binary data can be stored external to the resource object, in which case the destructor is responsible for releasing the data.

Several binary terms can be managed by the same resource object. The destructor is not called until the last binary is garbage collected. This can be useful to return different parts of a larger binary buffer.

As with enif_make_resource, no ownership transfer is done. The resource still needs to be released with enif_release_resource.

Sets *list_out to the reverse list of the list list_in and returns true, or returns false if list_in is not a list.

This function is only to be used on short lists, as a copy is created of the list, which is not released until after the NIF returns.

The list_in term must belong to environment env.

Creates a list containing the characters of the NULL-terminated string string with encoding encoding.

Creates a list containing the characters of the string string with length len and encoding encoding. NULL characters are treated as any other characters.

Makes a subbinary of binary bin_term, starting at zero-based position pos with a length of size bytes. bin_term must be a binary or bitstring. pos+size must be less or equal to the number of whole bytes in bin_term.

Creates a tuple term of arity cnt. Expects cnt number of arguments (after cnt) of type ERL_NIF_TERM as the elements of the tuple.

Creates a tuple term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_tuple to get a compile-time error if the number of arguments does not match.

Creates a tuple containing the elements of array arr of length cnt.

Creates an integer term from an unsigned int.

Creates an integer term from an unsigned 64-bit integer.

Creates an integer term from an unsigned long int.

Returns a unique integer with the same properties as specified by erlang:unique_integer/1.

env is the environment to create the integer in.

ERL_NIF_UNIQUE_POSITIVE and ERL_NIF_UNIQUE_MONOTONIC can be passed as the second argument to change the properties of the integer returned. They can be combined by OR:ing the two values together.

See also ErlNifUniqueInteger.

Creates an iterator for the map map by initializing the structure pointed to by iter. Argument entry determines the start position of the iterator: ERL_NIF_MAP_ITERATOR_FIRST or ERL_NIF_MAP_ITERATOR_LAST.

Returns true on success, or false if map is not a map.

A map iterator is only useful during the lifetime of environment env that the map belongs to. The iterator must be destroyed by calling enif_map_iterator_destroy:

ERL_NIF_TERM key, value;
ErlNifMapIterator iter;
enif_map_iterator_create(env, my_map, &iter, ERL_NIF_MAP_ITERATOR_FIRST);

while (enif_map_iterator_get_pair(env, &iter, &key, &value)) {
    do_something(key,value);
    enif_map_iterator_next(env, &iter);
}
enif_map_iterator_destroy(env, &iter);

Destroys a map iterator created by enif_map_iterator_create.

Gets key and value terms at the current map iterator position.

On success, sets *key and *value and returns true. Returns false if the iterator is positioned at head (before first entry) or tail (beyond last entry).

Returns true if map iterator iter is positioned before the first entry.

Returns true if map iterator iter is positioned after the last entry.

Increments map iterator to point to the next key-value entry.

Returns true if the iterator is now positioned at a valid key-value entry, or false if the iterator is positioned at the tail (beyond the last entry).

Decrements map iterator to point to the previous key-value entry.

Returns true if the iterator is now positioned at a valid key-value entry, or false if the iterator is positioned at the head (before the first entry).

Returns the current Erlang monotonic time. Notice that it is not uncommon with negative values.

time_unit is the time unit of the returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument, or if called from a thread that is not a scheduler thread.

See also ErlNifTime and ErlNifTimeUnit.

Same as erl_drv_mutex_create.

Same as erl_drv_mutex_destroy.

Same as erl_drv_mutex_lock.

Same as erl_drv_mutex_trylock.

Same as erl_drv_mutex_unlock.

Returns an erlang:now() time stamp.

This function is deprecated.

Creates or takes over a resource type identified by the string name and gives it the destructor function pointed to by dtor. Argument flags can have the following values:

ERL_NIF_RT_CREATE

Creates a new resource type that does not already exist.

ERL_NIF_RT_TAKEOVER

Opens an existing resource type and takes over ownership of all its instances. The supplied destructor dtor is called both for existing instances and new instances not yet created by the calling NIF library.

The two flag values can be combined with bitwise OR. The resource type name is local to the calling module. Argument module_str is not (yet) used and must be NULL. dtor can be NULL if no destructor is needed.

On success, the function returns a pointer to the resource type and *tried is set to either ERL_NIF_RT_CREATE or ERL_NIF_RT_TAKEOVER to indicate what was done. On failure, returns NULL and sets *tried to flags. It is allowed to set tried to NULL.

Notice that enif_open_resource_type is only allowed to be called in the three callbacks load, reload, and upgrade.

Works as erlang:port_command/2, except that it is always completely asynchronous.

env

The environment of the calling process. Must not be NULL.

*to_port

The port ID of the receiving port. The port ID is to refer to a port on the local node.

msg_env

The environment of the message term. Can be a process-independent environment allocated with enif_alloc_env or NULL.

msg

The message term to send. The same limitations apply as on the payload to erlang:port_command/2.

Using a msg_env of NULL is an optimization, which groups together calls to enif_alloc_env, enif_make_copy, enif_port_command, and enif_free_env into one call. This optimization is only useful when a majority of the terms are to be copied from env to msg_env.

Returns true if the command is successfully sent. Returns false if the command fails, for example:

• *to_port does not refer to a local port.
• The currently executing process (that is, the sender) is not alive.
• msg is invalid.

See also enif_get_local_port.

Returns the pointer to the private data that was set by load, reload, or upgrade.

Was previously named enif_get_data.

Creates an error exception with the term reason to be returned from a NIF, and associates it with environment env. Once a NIF or any function it calls invokes enif_raise_exception, the runtime ensures that the exception it creates is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.

The return value from enif_raise_exception can only be used as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception, but not to any other NIF API function.

See also enif_has_pending_exception and enif_make_badarg.

Changes the size of a binary bin. The source binary can be read-only, in which case it is left untouched and a mutable copy is allocated and assigned to *bin.

Returns true on success, or false if memory allocation failed.

Releases a binary obtained from enif_alloc_binary.

Removes a reference to resource object objobtained from enif_alloc_resource. The resource object is destructed when the last reference is removed. Each call to enif_release_resource must correspond to a previous call to enif_alloc_resource or enif_keep_resource. References made by enif_make_resource can only be removed by the garbage collector.

Same as erl_drv_rwlock_create.

Same as erl_drv_rwlock_destroy.

Same as erl_drv_rwlock_rlock.

Same as erl_drv_rwlock_runlock.

Same as erl_drv_rwlock_rwlock.

Same as erl_drv_rwlock_rwunlock.

Same as erl_drv_rwlock_tryrlock.

Same as erl_drv_rwlock_tryrwlock.

Schedules NIF fp to execute. This function allows an application to break up long-running work into multiple regular NIF calls or to schedule a dirty NIF to execute on a dirty scheduler thread.

The dirty NIF functionality described here is experimental. You have to enable support for dirty schedulers when building OTP to try out the functionality.

fun_name

Provides a name for the NIF that is scheduled for execution. If it cannot be converted to an atom, enif_schedule_nif returns a badarg exception.

flags

Must be set to 0 for a regular NIF. If the emulator was built with the experimental dirty scheduler support enabled, flags can be set to either ERL_NIF_DIRTY_JOB_CPU_BOUND if the job is expected to be CPU-bound, or ERL_NIF_DIRTY_JOB_IO_BOUND for jobs that will be I/O-bound. If dirty scheduler threads are not available in the emulator, an attempt to schedule such a job results in a badarg exception.

argc and argv

Can either be the originals passed into the calling NIF, or can be values created by the calling NIF.

The calling NIF must use the return value of enif_schedule_nif as its own return value.

Be aware that enif_schedule_nif, as its name implies, only schedules the NIF for future execution. The calling NIF does not block waiting for the scheduled NIF to execute and return. This means that the calling NIF cannot expect to receive the scheduled NIF return value and use it for further operations.

Initializes the pid variable *pid to represent the calling process.

Returns pid.

Sends a message to a process.

env

The environment of the calling process. Must be NULL only if calling from a created thread.

*to_pid

The pid of the receiving process. The pid is to refer to a process on the local node.

msg_env

The environment of the message term. Must be a process-independent environment allocated with enif_alloc_env or NULL.

msg

The message term to send.

Returns true if the message is successfully sent. Returns false if the send operation fails, that is:

• *to_pid does not refer to an alive local process.
• The currently executing process (that is, the sender) is not alive.

The message environment msg_env with all its terms (including msg) is invalidated by a successful call to enif_send. The environment is to either be freed with enif_free_env of cleared for reuse with enif_clear_env.

If msg_env is set to NULL, the msg term is copied and the original term and its environemt is still valid after the call.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Gets the byte size of resource object obj obtained by enif_alloc_resource.

Similar to snprintf but this format string also accepts "%T", which formats Erlang terms.

Same as driver_system_info.

Allocates a new binary with enif_alloc_binary and stores the result of encoding term according to the Erlang external term format.

Returns true on success, or false if the allocation fails.

See also erlang:term_to_binary/1 and enif_binary_to_term.

Same as erl_drv_thread_create.

Same as erl_drv_thread_exit.

Same as erl_drv_thread_join.

Same as erl_drv_thread_opts_create.

Same as erl_drv_thread_opts_destroy.

Same as erl_drv_thread_self.

Determine the type of currently executing thread. A positive value indicates a scheduler thread while a negative value or zero indicates another type of thread. Currently the following specific types exist (which may be extended in the future):

ERL_NIF_THR_UNDEFINED

Undefined thread that is not a scheduler thread.

ERL_NIF_THR_NORMAL_SCHEDULER

A normal scheduler thread.

ERL_NIF_THR_DIRTY_CPU_SCHEDULER

A dirty CPU scheduler thread.

ERL_NIF_THR_DIRTY_IO_SCHEDULER

A dirty I/O scheduler thread.

Returns the current time offset between Erlang monotonic time and Erlang system time converted into the time_unit passed as argument.

time_unit is the time unit of the returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument or if called from a thread that is not a scheduler thread.

See also ErlNifTime and ErlNifTimeUnit.

Same as erl_drv_tsd_get.

Same as erl_drv_tsd_key_create.

Same as erl_drv_tsd_key_destroy.

Same as erl_drv_tsd_set.

erlang:load_nif/2