View Source fprof (tools v4.0)
A Time Profiling Tool using trace to file for minimal runtime performance impact.
This module is used to profile a program to find out how the execution time is used. Trace to file is used to minimize runtime performance impact.
The fprof
module uses tracing to collect profiling data, hence there is no
need for special compilation of any module to be profiled. When it starts
tracing, fprof
will erase all previous tracing in the node and set the
necessary trace flags on the profiling target processes as well as local call
trace on all functions in all loaded modules and all modules to be loaded.
fprof
erases all tracing in the node when it stops tracing.
fprof
presents both own time i.e how much time a function has used for its
own execution, and accumulated time i.e including called functions. All
presented times are collected using trace timestamps. fprof
tries to collect
cpu time timestamps, if the host machine OS supports it. Therefore the times may
be wallclock times and OS scheduling will randomly strike all called functions
in a presumably fair way.
If, however, the profiling time is short, and the host machine OS does not support high resolution cpu time measurements, some few OS schedulings may show up as ridiculously long execution times for functions doing practically nothing. An example of a function more or less just composing a tuple in about 100 times the normal execution time has been seen, and when the tracing was repeated, the execution time became normal.
Profiling is essentially done in 3 steps:
1
- Tracing; to file, as mentioned in the previous paragraph. The trace contains entries for function calls, returns to function, process scheduling, other process related (spawn, etc) events, and garbage collection. All trace entries are timestamped.2
- Profiling; the trace file is read, the execution call stack is simulated, and raw profile data is calculated from the simulated call stack and the trace timestamps. The profile data is stored in thefprof
server state. During this step the trace data may be dumped in text format to file or console.3
- Analysing; the raw profile data is sorted, filtered and dumped in text format either to file or console. The text format intended to be both readable for a human reader, as well as parsable with the standard erlang parsing tools.
Since fprof
uses trace to file, the runtime performance degradation is
minimized, but still far from negligible, especially for programs that use the
filesystem heavily by themselves. Where you place the trace file is also
important, e.g on Solaris /tmp
is usually a good choice since it is
essentially a RAM disk, while any NFS (network) mounted disk is a bad idea.
fprof
can also skip the file step and trace to a tracer process that does the
profiling in runtime.
Analysis format
This section describes the output format of the analyse command. See
analyse/0
.
The format is parsable with the standard Erlang parsing tools erl_scan
and
erl_parse
, file:consult/1
or io:read/2
. The parse format is not explained
here - it should be easy for the interested to try it out. Note that some flags
to analyse/1
will affect the format.
The following example was run on OTP/R8 on Solaris 8, all OTP internals in this example are very version dependent.
As an example, we will use the following function, that you may recognise as a slightly modified benchmark function from the manpage file(3):
-module(foo).
-export([create_file_slow/2]).
create_file_slow(Name, N) when is_integer(N), N >= 0 ->
{ok, FD} =
file:open(Name, [raw, write, delayed_write, binary]),
if N > 256 ->
ok = file:write(FD,
lists:map(fun (X) -> <<X:32/unsigned>> end,
lists:seq(0, 255))),
ok = create_file_slow(FD, 256, N);
true ->
ok = create_file_slow(FD, 0, N)
end,
ok = file:close(FD).
create_file_slow(FD, M, M) ->
ok;
create_file_slow(FD, M, N) ->
ok = file:write(FD, <<M:32/unsigned>>),
create_file_slow(FD, M+1, N).
Let us have a look at the printout after running:
1> fprof:apply(foo, create_file_slow, [junk, 1024]).
2> fprof:profile().
3> fprof:analyse().
The printout starts with:
%% Analysis results:
{ analysis_options,
[{callers, true},
{sort, acc},
{totals, false},
{details, true}]}.
% CNT ACC OWN
[{ totals, 9627, 1691.119, 1659.074}]. %%%
The CNT column shows the total number of function calls that was found in the trace. In the ACC column is the total time of the trace from first timestamp to last. And in the OWN column is the sum of the execution time in functions found in the trace, not including called functions. In this case it is very close to the ACC time since the emulator had practically nothing else to do than to execute our test program.
All time values in the printout are in milliseconds.
The printout continues:
% CNT ACC OWN
[{ "<0.28.0>", 9627,undefined, 1659.074}]. %%
This is the printout header of one process. The printout contains only this one
process since we did fprof:apply/3
which traces only the current process.
Therefore the CNT and OWN columns perfectly matches the totals above. The ACC
column is undefined since summing the ACC times of all calls in the process
makes no sense - you would get something like the ACC value from totals above
multiplied by the average depth of the call stack, or something.
All paragraphs up to the next process header only concerns function calls within this process.
Now we come to something more interesting:
{[{undefined, 0, 1691.076, 0.030}],
{ {fprof,apply_start_stop,4}, 0, 1691.076, 0.030}, %
[{{foo,create_file_slow,2}, 1, 1691.046, 0.103},
{suspend, 1, 0.000, 0.000}]}.
{[{{fprof,apply_start_stop,4}, 1, 1691.046, 0.103}],
{ {foo,create_file_slow,2}, 1, 1691.046, 0.103}, %
[{{file,close,1}, 1, 1398.873, 0.019},
{{foo,create_file_slow,3}, 1, 249.678, 0.029},
{{file,open,2}, 1, 20.778, 0.055},
{{lists,map,2}, 1, 16.590, 0.043},
{{lists,seq,2}, 1, 4.708, 0.017},
{{file,write,2}, 1, 0.316, 0.021}]}.
The printout consists of one paragraph per called function. The function
marked with '%' is the one the paragraph concerns - foo:create_file_slow/2
.
Above the marked function are the calling functions - those that has called
the marked, and below are those called by the marked function.
The paragraphs are per default sorted in decreasing order of the ACC column for the marked function. The calling list and called list within one paragraph are also per default sorted in decreasing order of their ACC column.
The columns are: CNT - the number of times the function has been called, ACC - the time spent in the function including called functions, and OWN - the time spent in the function not including called functions.
The rows for the calling functions contain statistics for the marked function with the constraint that only the occasions when a call was made from the row's function to the marked function are accounted for.
The row for the marked function simply contains the sum of all calling rows.
The rows for the called functions contains statistics for the row's function with the constraint that only the occasions when a call was made from the marked to the row's function are accounted for.
So, we see that foo:create_file_slow/2
used very little time for its own
execution. It spent most of its time in file:close/1
. The function
foo:create_file_slow/3
that writes 3/4 of the file contents is the second
biggest time thief.
We also see that the call to file:write/2
that writes 1/4 of the file contents
takes very little time in itself. What takes time is to build the data
(lists:seq/2
and lists:map/2
).
The function 'undefined' that has called fprof:apply_start_stop/4
is an
unknown function because that call was not recorded in the trace. It was only
recorded that the execution returned from fprof:apply_start_stop/4
to some
other function above in the call stack, or that the process exited from there.
Let us continue down the printout to find:
{[{{foo,create_file_slow,2}, 1, 249.678, 0.029},
{{foo,create_file_slow,3}, 768, 0.000, 23.294}],
{ {foo,create_file_slow,3}, 769, 249.678, 23.323}, %
[{{file,write,2}, 768, 220.314, 14.539},
{suspend, 57, 6.041, 0.000},
{{foo,create_file_slow,3}, 768, 0.000, 23.294}]}.
If you compare with the code you will see there also that
foo:create_file_slow/3
was called only from foo:create_file_slow/2
and
itself, and called only file:write/2
, note the number of calls to
file:write/2
. But here we see that suspend
was called a few times. This is a
pseudo function that indicates that the process was suspended while executing in
foo:create_file_slow/3
, and since there is no receive
or erlang:yield/0
in
the code, it must be Erlang scheduling suspensions, or the trace file driver
compensating for large file write operations (these are regarded as a schedule
out followed by a schedule in to the same process).
Let us find the suspend
entry:
{[{{file,write,2}, 53, 6.281, 0.000},
{{foo,create_file_slow,3}, 57, 6.041, 0.000},
{{prim_file,drv_command,4}, 50, 4.582, 0.000},
{{prim_file,drv_get_response,1}, 34, 2.986, 0.000},
{{lists,map,2}, 10, 2.104, 0.000},
{{prim_file,write,2}, 17, 1.852, 0.000},
{{erlang,port_command,2}, 15, 1.713, 0.000},
{{prim_file,drv_command,2}, 22, 1.482, 0.000},
{{prim_file,translate_response,2}, 11, 1.441, 0.000},
{{prim_file,'-drv_command/2-fun-0-',1}, 15, 1.340, 0.000},
{{lists,seq,4}, 3, 0.880, 0.000},
{{foo,'-create_file_slow/2-fun-0-',1}, 5, 0.523, 0.000},
{{erlang,bump_reductions,1}, 4, 0.503, 0.000},
{{prim_file,open_int_setopts,3}, 1, 0.165, 0.000},
{{prim_file,i32,4}, 1, 0.109, 0.000},
{{fprof,apply_start_stop,4}, 1, 0.000, 0.000}],
{ suspend, 299, 32.002, 0.000}, %
[ ]}.
We find no particularly long suspend times, so no function seems to have waited
in a receive statement. Actually, prim_file:drv_command/4
contains a receive
statement, but in this test program, the message lies in the process receive
buffer when the receive statement is entered. We also see that the total suspend
time for the test run is small.
The suspend
pseudo function has got an OWN time of zero. This is to prevent
the process total OWN time from including time in suspension. Whether suspend
time is really ACC or OWN time is more of a philosophical question.
Now we look at another interesting pseudo function, garbage_collect
:
{[{{prim_file,drv_command,4}, 25, 0.873, 0.873},
{{prim_file,write,2}, 16, 0.692, 0.692},
{{lists,map,2}, 2, 0.195, 0.195}],
{ garbage_collect, 43, 1.760, 1.760}, %
[ ]}.
Here we see that no function distinguishes itself considerably, which is very normal.
The garbage_collect
pseudo function has not got an OWN time of zero like
suspend
, instead it is equal to the ACC time.
Garbage collect often occurs while a process is suspended, but fprof
hides
this fact by pretending that the suspended function was first unsuspended and
then garbage collected. Otherwise the printout would show garbage_collect
being called from suspend
but not which function that might have caused the
garbage collection.
Let us now get back to the test code:
{[{{foo,create_file_slow,3}, 768, 220.314, 14.539},
{{foo,create_file_slow,2}, 1, 0.316, 0.021}],
{ {file,write,2}, 769, 220.630, 14.560}, %
[{{prim_file,write,2}, 769, 199.789, 22.573},
{suspend, 53, 6.281, 0.000}]}.
Not unexpectedly, we see that file:write/2
was called from
foo:create_file_slow/3
and foo:create_file_slow/2
. The number of calls in
each case as well as the used time are also just confirms the previous results.
We see that file:write/2
only calls prim_file:write/2
, but let us refrain
from digging into the internals of the kernel application.
But, if we nevertheless do dig down we find the call to the linked in driver that does the file operations towards the host operating system:
{[{{prim_file,drv_command,4}, 772, 1458.356, 1456.643}],
{ {erlang,port_command,2}, 772, 1458.356, 1456.643}, %
[{suspend, 15, 1.713, 0.000}]}.
This is 86 % of the total run time, and as we saw before it is the close operation the absolutely biggest contributor. We find a comparison ratio a little bit up in the call stack:
{[{{prim_file,close,1}, 1, 1398.748, 0.024},
{{prim_file,write,2}, 769, 174.672, 12.810},
{{prim_file,open_int,4}, 1, 19.755, 0.017},
{{prim_file,open_int_setopts,3}, 1, 0.147, 0.016}],
{ {prim_file,drv_command,2}, 772, 1593.322, 12.867}, %
[{{prim_file,drv_command,4}, 772, 1578.973, 27.265},
{suspend, 22, 1.482, 0.000}]}.
The time for file operations in the linked in driver distributes itself as 1 % for open, 11 % for write and 87 % for close. All data is probably buffered in the operating system until the close.
The unsleeping reader may notice that the ACC times for
prim_file:drv_command/2
and prim_file:drv_command/4
is not equal between the
paragraphs above, even though it is easy to believe that
prim_file:drv_command/2
is just a passthrough function.
The missing time can be found in the paragraph for prim_file:drv_command/4
where it is evident that not only prim_file:drv_command/2
is called but also a
fun:
{[{{prim_file,drv_command,2}, 772, 1578.973, 27.265}],
{ {prim_file,drv_command,4}, 772, 1578.973, 27.265}, %
[{{erlang,port_command,2}, 772, 1458.356, 1456.643},
{{prim_file,'-drv_command/2-fun-0-',1}, 772, 87.897, 12.736},
{suspend, 50, 4.582, 0.000},
{garbage_collect, 25, 0.873, 0.873}]}.
And some more missing time can be explained by the fact that
prim_file:open_int/4
both calls prim_file:drv_command/2
directly as well as
through prim_file:open_int_setopts/3
, which complicates the picture.
{[{{prim_file,open,2}, 1, 20.309, 0.029},
{{prim_file,open_int,4}, 1, 0.000, 0.057}],
{ {prim_file,open_int,4}, 2, 20.309, 0.086}, %
[{{prim_file,drv_command,2}, 1, 19.755, 0.017},
{{prim_file,open_int_setopts,3}, 1, 0.360, 0.032},
{{prim_file,drv_open,2}, 1, 0.071, 0.030},
{{erlang,list_to_binary,1}, 1, 0.020, 0.020},
{{prim_file,i32,1}, 1, 0.017, 0.017},
{{prim_file,open_int,4}, 1, 0.000, 0.057}]}.
.
.
.
{[{{prim_file,open_int,4}, 1, 0.360, 0.032},
{{prim_file,open_int_setopts,3}, 1, 0.000, 0.016}],
{ {prim_file,open_int_setopts,3}, 2, 0.360, 0.048}, %
[{suspend, 1, 0.165, 0.000},
{{prim_file,drv_command,2}, 1, 0.147, 0.016},
{{prim_file,open_int_setopts,3}, 1, 0.000, 0.016}]}.
Notes
The actual supervision of execution times is in itself a CPU intensive activity. A message is written on the trace file for every function call that is made by the profiled code.
The ACC time calculation is sometimes difficult to make correct, since it is difficult to define. This happens especially when a function occurs in several instances in the call stack, for example by calling itself perhaps through other functions and perhaps even non-tail recursively.
To produce sensible results, fprof
tries not to charge any function more than
once for ACC time. The instance highest up (with longest duration) in the call
stack is chosen.
Sometimes a function may unexpectedly waste a lot (some 10 ms or more depending
on host machine OS) of OWN (and ACC) time, even functions that do practically
nothing at all. The problem may be that the OS has chosen to schedule out the
Erlang runtime system process for a while, and if the OS does not support high
resolution cpu time measurements fprof
will use wallclock time for its
calculations, and it will appear as functions randomly burn virtual machine
time.
See Also
dbg(3), eprof
(3), erlang(3), io(3), Tools User's Guide
Summary
Functions
Same as analyse([])
.
Same as analyse([OptionName])
.
Same as apply(Func, Args, [])
.
Same as profile([])
.
Same as profile([OptionName])
.
Starts the fprof
server.
Same as stop(normal)
.
Stops the fprof
server.
Same as trace([start, verbose])
.
Same as trace([start, {file, Filename}])
.
Types
-type analyse_option() :: append | callers | {callers, boolean()} | {cols, Cols :: non_neg_integer()} | dest | {dest, Dest :: pid() | (Destfile :: file:filename())} | details | {details, boolean()} | no_callers | no_details | {sort, SortSpec :: acc | own} | totals | {totals, boolean()}.
-type apply_option() :: continue | {procs, PidList :: [pid()]} | start | (TraceStartOption :: trace_option()).
-type profile_option() :: append | dump | {dump, pid() | (Dump :: (Dumpfile :: file:filename() | []))} | file | {file, Filename :: file:filename()} | start | stop.
Functions
-spec analyse() -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when ServerPid :: pid(), Reason :: term().
Same as analyse([])
.
-spec analyse(OptionName) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), ServerPid :: pid(), Reason :: term(); ({OptionName, OptionValue}) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term(); (OptionList) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionList :: [Option], Option :: analyse_option(), ServerPid :: pid(), Reason :: term().
Same as analyse([OptionName])
.
Same as analyse([{OptionName, OptionValue}])
.
Analyses raw profile data in the fprof
server. If called while there is no raw
profile data available, {error, no_profile}
is returned.
Destfile
is used to call file:open/2
.
Option description:
dest
|{dest, Dest}
- Specifies the destination for the analysis. If this option is not given or it isdest
, the destination will be the caller's group leader, otherwise the destinationDest
is either thepid/0
of an I/O device or a filename. And, finally, if the filename is[]
-"fprof.analysis"
is used instead.append
- Causes the analysis to be appended to the destination file. This option is only allowed with the{dest, Destfile}
option.{cols, Cols}
- Specifies the number of columns in the analysis text. If this option is not given the number of columns is set to 80.callers
|{callers, true}
- Prints callers and called information in the analysis. This is the default.{callers, false}
|no_callers
- Suppresses the printing of callers and called information in the analysis.{sort, SortSpec}
- Specifies if the analysis should be sorted according to the ACC column, which is the default, or the OWN column. See Analysis Format below.totals
|{totals, true}
- Includes a section containing call statistics for all calls regardless of process, in the analysis.{totals, false}
- Suppresses the totals section in the analysis, which is the default.details
|{details, true}
- Prints call statistics for each process in the analysis. This is the default.{details, false}
|no_details
- Suppresses the call statistics for each process from the analysis.
-spec analyse(OptionName, OptionValue) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term().
Same as analyse([{OptionName, OptionValue}])
.
-spec apply(Func, Args) -> term() when Func :: fun() | {Module :: module(), Function :: atom()}, Args :: [term()].
Same as apply(Func, Args, [])
.
-spec apply(Module, Function, Args) -> term() when Module :: module(), Function :: atom(), Args :: [term()]; (Func, Args, OptionList) -> term() when Func :: fun() | {Module :: module(), Function :: atom()}, Args :: [term()], OptionList :: [Option], Option :: apply_option().
Same as apply({Module, Function}, Args, [])
.
Calls erlang:apply(Func, Args)
surrounded by trace([start, ...])
and
trace(stop)
.
Some effort is made to keep the trace clean from unnecessary trace messages;
tracing is started and stopped from a spawned process while the erlang:apply/2
call is made in the current process, only surrounded by receive
and send
statements towards the trace starting process. The trace starting process exits
when not needed any more.
The TraceStartOption
is any option allowed for trace/1
. The options
[start, {procs, [self() | PidList]} | OptList]
are given to
trace/1
, where OptList
is OptionList
with continue
, start
and {procs, _}
options removed.
The continue
option inhibits the call to trace(stop)
and leaves
it up to the caller to stop tracing at a suitable time.
-spec apply(Module, Function, Args, OptionList) -> term() when Module :: module(), Function :: atom(), Args :: [term()], OptionList :: [Option], Option :: apply_option().
Same as apply({Module, Function}, Args, OptionList)
.
OptionList
is an option list allowed for apply/3
.
-spec profile() -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when ServerPid :: pid(), Reason :: term().
Same as profile([])
.
-spec profile(OptionName) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), Tracer :: pid(), ServerPid :: pid(), Reason :: term(); ({OptionName, OptionValue}) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), Tracer :: pid(), ServerPid :: pid(), Reason :: term(); (OptionList) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionList :: [Option], Option :: profile_option(), Tracer :: pid(), ServerPid :: pid(), Reason :: term().
Same as profile([OptionName])
.
Same as profile([{OptionName, OptionValue}])
.
Compiles a trace into raw profile data held by the fprof
server.
Dumpfile
is used to call file:open/2
, and Filename
is used to call
dbg:trace_port(file, Filename)
. Please see file:open/2
and
dbg:trace_port/2
.
Option description:
file
|{file, Filename}
- Reads the fileFilename
and creates raw profile data that is stored in RAM by thefprof
server. If the optionfile
is given, or none of these options are given, the file"fprof.trace"
is read. The call will return when the whole trace has been read with the return valueok
if successful. This option is not allowed with thestart
orstop
options.dump
|{dump, Dump}
- Specifies the destination for the trace text dump. If this option is not given, no dump is generated, if it isdump
the destination will be the caller's group leader, otherwise the destinationDump
is either the pid of an I/O device or a filename. And, finally, if the filename is[]
-"fprof.dump"
is used instead. This option is not allowed with thestop
option.append
- Causes the trace text dump to be appended to the destination file. This option is only allowed with the{dump, Dumpfile}
option.start
- Starts a tracer process that profiles trace data in runtime. The call will return immediately with the return value{ok, Tracer}
if successful. This option is not allowed with thestop
,file
or{file, Filename}
options.stop
- Stops the tracer process that profiles trace data in runtime. The return value will be valueok
if successful. This option is not allowed with thestart
,file
or{file, Filename}
options.
-spec profile(OptionName, OptionValue) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), Tracer :: pid(), ServerPid :: pid(), Reason :: term().
Same as profile([{OptionName, OptionValue}])
.
-spec start() -> {ok, Pid} | {error, {already_started, Pid}} when Pid :: pid().
Starts the fprof
server.
Note that it seldom needs to be started explicitly since it is automatically started by the functions that need a running server.
-spec stop() -> ok.
Same as stop(normal)
.
-spec stop(Reason) -> ok when Reason :: term().
Stops the fprof
server.
The supplied Reason
becomes the exit reason for the server process. Default
Any Reason
other than kill
sends a request to the server and waits for it to
clean up, reply and exit. If Reason
is kill
, the server is bluntly killed.
If the fprof
server is not running, this function returns immediately with the
same return value.
Note
When the
fprof
server is stopped the collected raw profile data is lost.
-spec trace(verbose) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when ServerPid :: pid(), Reason :: term(); (OptionName) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), ServerPid :: pid(), Reason :: term(); ({OptionName, OptionValue}) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term(); (OptionList) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionList :: [Option], Option :: trace_option(), ServerPid :: pid(), Reason :: term().
Same as trace([start, verbose])
.
Same as trace([OptionName])
.
Same as trace([{OptionName, OptionValue}])
.
Starts or stops tracing.
PidSpec
and Tracer
are used in calls to
erlang:trace(PidSpec, true, [{tracer, Tracer} | Flags])
, and Filename
is
used to call dbg:trace_port(file, Filename)
. Please see erlang:trace/3
and
dbg:trace_port/2
.
Option description:
stop
- Stops a runningfprof
trace and clears all tracing from the node. Either optionstop
orstart
must be specified, but not both.start
- Clears all tracing from the node and starts a newfprof
trace. Either optionstart
orstop
must be specified, but not both.verbose
|{verbose, boolean()}
- The optionsverbose
or{verbose, true}
adds some trace flags thatfprof
does not need, but that may be interesting for general debugging purposes. This option is only allowed with thestart
option.cpu_time
|{cpu_time, boolean()}
- The optionscpu_time
or{cpu_time, true}
makes the timestamps in the trace be in CPU time instead of wallclock time which is the default. This option is only allowed with thestart
option.Warning
Getting correct values out of cpu_time can be difficult. The best way to get correct values is to run using a single scheduler and bind that scheduler to a specific CPU, i.e.
erl +S 1 +sbt db
.{procs, PidSpec}
|{procs, [PidSpec]}
- Specifies which processes that shall be traced. If this option is not given, the calling process is traced. All processes spawned by the traced processes are also traced. This option is only allowed with thestart
option.file
|{file, Filename}
- Specifies the filename of the trace. If the optionfile
is given, or none of these options are given, the file"fprof.trace"
is used. This option is only allowed with thestart
option, but not with the{tracer, Tracer}
option.{tracer, Tracer}
- Specifies that trace to process or port shall be done instead of trace to file. This option is only allowed with thestart
option, but not with the{file, Filename}
option.
-spec trace(start, Filename) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when Filename :: file:filename(), ServerPid :: pid(), Reason :: term(); (verbose, Filename) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when Filename :: file:filename(), ServerPid :: pid(), Reason :: term(); (OptionName, OptionValue) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term().
Same as trace([start, {file, Filename}])
.
Same as trace([start, verbose, {file, Filename}])
.
Same as trace([{OptionName, OptionValue}])
.