View Source dyntrace (runtime_tools v2.1)
Interface to dynamic tracing
This module implements interfaces to dynamic tracing, should such be compiled into the virtual machine. For a standard and/or commercial build, no dynamic tracing is available, in which case none of the functions in this module is usable or give any effect.
Should dynamic tracing be enabled in the current build, either by configuring
with ./configure --with-dynamic-trace=dtrace
or with
./configure --with-dynamic-trace=systemtap
, the module can be used for two
things:
- Trigger the user-probe
user_trace_i4s4
in the NIF librarydyntrace.so
by callingdyntrace:p/{1,2,3,4,5,6,7,8}
. - Set a user specified tag that will be present in the trace messages of both
the
efile_drv
and the user-probe mentioned above.
Both building with dynamic trace probes and using them is experimental and unsupported by Erlang/OTP. It is included as an option for the developer to trace and debug performance issues in their systems.
The original implementation is mostly done by Scott Lystiger Fritchie as an Open Source Contribution and it should be viewed as such even though the source for dynamic tracing as well as this module is included in the main distribution. However, the ability to use dynamic tracing of the virtual machine is a very valuable contribution which OTP has every intention to maintain as a tool for the developer.
How to write d
programs or systemtap
scripts can be learned from books and
from a lot of pages on the Internet. This manual page does not include any
documentation about using the dynamic trace tools of respective platform. The
examples
directory of the runtime_tools
application however contains
comprehensive examples of both d
and systemtap
programs that will help you
get started. Another source of information is the dtrace and
systemtap chapters in the Runtime Tools Users' Guide.
Summary
Functions
available() -> boolean()
get_tag() -> binary() | undefined
p() -> true | false | error | badarg
p(integer() | string()) -> true | false | error | badarg
p(integer() | string(), integer() | string()) -> true | false | error | badarg
p(integer() | string(), integer() | string(), integer() | string()) -> true | false | error | badarg
p(integer() | string(), integer() | string(), integer() | string(), integer() | string()) -> true | false | error | badarg
p(integer(), integer() | string(), integer() | string(), integer() | string(), |
string()) -> true | false | error | badarg |
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters, as in p/2
.
p(integer(), integer(), integer() | string(), integer() | string(), string(), string()) -> true | false | error | badarg
p(integer(), integer(), integer(), integer() | string(), string(), string(), string()) -> true | false | error | badarg
p(integer(), integer(), integer(), integer(), string(), string(), string(), string()) -> true | false | error | badarg
put_tag(Item) -> binary() | undefined
restore_tag(TagData) -> true
spread_tag(boolean()) -> TagData
Types
Functions
-spec available() -> true | false.
available() -> boolean()
This function uses the NIF library to determine if dynamic tracing is available.
Usually calling erlang:system_info/1
is a better indicator of the availability
of dynamic tracing.
The function will throw an exception if the dyntrace
NIF library could not be
loaded by the on_load function of this module.
-spec get_tag() -> binary() | undefined.
get_tag() -> binary() | undefined
This function returns the user tag set in the current process. If no tag is set
or dynamic tracing is not available, it returns undefined
This function returns the user tag set in the current process or, if no user tag
is present, the last user tag sent to the process together with a message (in
the same way as sequential trace tokens are spread to other
processes together with messages. For an explanation of how user tags can be
spread together with messages, see spread_tag/1
. If no tag is found or dynamic
tracing is not available, it returns undefined
-spec p() -> true | false | error | badarg.
p() -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the dyntrace NIF module, sending a trace message only containing the user tag and zeroes/empty strings in all other fields.
-spec p(probe_arg()) -> true | false | error | badarg.
p(integer() | string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the dyntrace NIF module, sending a trace message containing the user tag and the integer or string parameter in the first integer/string field.
p(integer() | string(), integer() | string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters. I.e.
p(1,"Hello")
is ok, as is p(1,1)
and
p("Hello","Again")
, but not p("Hello",1)
.
p(integer() | string(), integer() | string(), integer() | string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters, as in p/2
.
p(integer() | string(), integer() | string(), integer() | string(), integer() | string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters, as in p/2
.
-spec p(probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg()) -> true | false | error | badarg.
p(integer(), integer() | string(), integer() | string(), integer() | string(), |
string()) -> true | false | error | badarg |
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters, as in p/2
.
There can be no more than four parameters of any type (integer() or string()), so the first parameter has to be an integer() and the last a string().
-spec p(probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg()) -> true | false | error | badarg.
p(integer(), integer(), integer() | string(), integer() | string(), string(), string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters, as in p/2
.
There can be no more than four parameters of any type (integer() or string()), so the first two parameters has to be integer()'s and the last two string()'s.
-spec p(probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg()) -> true | false | error | badarg.
p(integer(), integer(), integer(), integer() | string(), string(), string(), string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the
dyntrace NIF module, sending a trace message containing the user tag and the
integer() or string() parameters as the first fields of respective type.
integer() parameters should be put before any string() parameters, as in p/2
.
There can be no more than four parameters of any type (integer() or string()), so the first three parameters has to be integer()'s and the last three string()'s.
-spec p(probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg(), probe_arg()) -> true | false | error | badarg.
p(integer(), integer(), integer(), integer(), string(), string(), string(), string()) -> true | false | error | badarg
Calling this function will trigger the "user" trace probe user_trace_i4s4 in the dyntrace NIF module, sending a trace message containing all the integer()'s and string()'s provided, as well as any user tag set in the current process.
put_tag(Item) -> binary() | undefined
This function sets the user tag of the current process. The user tag is a binary(), but can be specified as any iodata(), which is automatically converted to a binary by this function.
The user tag is provided to the user probes triggered by calls top
dyntrace:p/{1,2,3,4,5,6,7,8}
as well as probes in the efile_driver. In the
future, user tags might be added to more probes.
The old user tag (if any) is returned, or undefined
if no user tag was present
or dynamic tracing is not enabled.
-spec restore_tag(true | {non_neg_integer(), binary() | []}) -> true.
restore_tag(TagData) -> true
Restores the previous state of user tags and their spreading as it was before a
call to spread_tag/1
. Note that the restoring is not limited to the same
process, one can utilize this to turn off spreding in one process and restore it
in a newly created, the one that actually is going to send messages:
f() ->
TagData=dyntrace:spread_tag(false),
spawn(fun() ->
dyntrace:restore_tag(TagData),
do_something()
end),
do_something_else(),
dyntrace:restore_tag(TagData).
Correctly handling user tags and their spreading might take some effort, as Erlang programs tend to send and receive messages so that sometimes the user tag gets lost due to various things, like double receives or communication with a port (ports do not handle user tags, in the same way as they do not handle regular sequential trace tokens).
-spec spread_tag(boolean()) -> true | {non_neg_integer(), binary() | []}.
spread_tag(boolean()) -> TagData
This function controls if user tags are to be spread to other processes with the next message. Spreading of user tags work like spreading of sequential trace tokens, so that a received user tag will be active in the process until the next message arrives (if that message does not also contain the user tag.
This functionality is used when a client process communicates with a file
i/o-server to spread the user tag to the I/O-server and then down to the
efile_drv driver. By using spread_tag/1
and
restore_tag/1
, one can enable or disable spreading of user
tags to other processes and then restore the previous state of the user tag. The
TagData returned from this call contains all previous information so the state
(including any previously spread user tags) will be completely restored by a
later call to restore_tag/1
.
The file
module already spread's tags, so there is no need to manually call
these function to get user tags spread to the efile driver through that module.
The most use of this function would be if one for example uses the io
module
to communicate with an I/O-server for a regular file, like in the following
example:
f() ->
{ok, F} = file:open("test.tst",[write]),
Saved = dyntrace:spread_tag(true),
io:format(F,"Hello world!",[]),
dyntrace:restore_tag(Saved),
file:close(F).
In this example, any user tag set in the calling process will be spread to the I/O-server when the io:format call is done.