The profiler API can be used by dynamically loaded profiler modules to monitor different aspects of a running program. The API is also usable by embedders without having to compile a profiler module.
A profiler module is simply a shared library with a single exported function which is the entry point that Mono calls at startup. It must have the following signature:
void mono_profiler_startup_example (const char *desc)
Here, the example
portion of the function name is
the name of the profiler module. It must match the shared library
name (i.e. libmono-profiler-example.so
). desc
is the set of arguments that were passed from the command line.
For example, a bare bones profiler module might look like this
(example.c
):
#include <mono/metadata/profiler.h>
#include <stdio.h>
struct _MonoProfiler {
int dummy;
}
static MonoProfiler profiler;
static void
runtime_inited (MonoProfiler *prof)
{
printf ("Hello World");
}
void
mono_profiler_init_example (const char *desc)
{
MonoProfilerHandle handle = mono_profiler_create (&profiler);
mono_profiler_set_runtime_initialized_callback (handle, runtime_inited);
}
To compile this module, a C compiler must be invoked in a similar fashion to this, on Linux:
gcc -fPIC -shared -o libmono-profiler-example.so example.c `pkg-config --cflags mono-2`
Or on OS X:
gcc -undefined suppress -flat_namespace -o libmono-profiler-example.so example.c `pkg-config --cflags mono-2`
You can then load the module using:
mono --profile=example hello.exe
(Note that adjusting LD_LIBRARY_PATH
may be
necessary in order for the dynamic linker to find the module.)
These are the functions usable for profiling programs.
Each function has a note indicating whether they're async safe. An async safe function can be invoked in a signal handler or when the world is stopped by the GC. Conversely, a function that is not async safe must not be invoked in such a context or undefined behavior can occur (crashes, deadlocks, etc).
Some functions may only be invoked from a profiler module's init function (or prior to running managed code in the case of embedding). This is noted explicitly only if applicable to a function.
These functions are used to load and install profilers.
mono_profiler_load
Loads a profiler module based on the specified description. desc can be
of the form name:args
or just name
. For example, log:sample
and
log
will both load libmono-profiler-log.so
. The description is passed
to the module after it has been loaded. If the specified module has already
been loaded, this function has no effect.
A module called foo
should declare an entry point like so:
void mono_profiler_init_foo (const char *desc)
{
}
This function is not async safe.
This function may only be called by embedders prior to running managed code.
mono_profiler_create
Installs a profiler and returns a handle for it. The handle is used with the
other functions in the profiler API (e.g. for setting up callbacks). The
given structure pointer, prof, will be passed to all callbacks from the
profiler API. It can be
.
NULL
Example usage:
struct _MonoProfiler {
int my_stuff;
// ...
};
MonoProfiler *prof = malloc (sizeof (MonoProfiler));
prof->my_stuff = 42;
MonoProfilerHandle handle = mono_profiler_create (prof);
mono_profiler_set_shutdown_callback (handle, my_shutdown_cb);
This function is not async safe.
This function may only be called from a profiler's init function or prior to running managed code.
mono_profiler_set_cleanup_callback
Sets a profiler cleanup function. This function will be invoked at shutdown
when the profiler API is cleaning up its internal structures. It's mainly
intended for a profiler to free the structure pointer that was passed to
mono_profiler_create
, if necessary.
This function is async safe.
These functions provide access to the JIT compiler's code coverage support. This functionality can be used to collect information about how many times certain code paths have been executed.
mono_profiler_enable_coverage
Enables support for code coverage instrumentation. At the moment, this means
enabling the debug info subsystem. If this function is not called, it will
not be possible to use mono_profiler_get_coverage_data
. Returns
if code coverage support was enabled, or TRUE
if the function was called
too late for this to be possible.
FALSE
This function is not async safe.
This function may only be called from a profiler's init function or prior to running managed code.
mono_profiler_set_coverage_filter_callback
Sets a code coverage filter function. The profiler API will invoke filter
functions from all installed profilers. If any of them return
, then
the given method will be instrumented for coverage analysis. All filters are
guaranteed to be called at least once per method, even if an earlier filter
has already returned TRUE
.
TRUE
Note that filter functions must be installed before a method is compiled in order to have any effect, i.e. a filter should be registered in a profiler's init function or prior to running managed code (if embedding).
This function is async safe.
mono_profiler_get_coverage_data
Retrieves all coverage data for method and invokes cb for each entry.
Source location information will only be filled out if method has debug
info available. Returns
if method was instrumented for code
coverage; otherwise, TRUE
.
FALSE
Please note that the structure passed to cb is only valid for the duration of the callback.
This function is not async safe.
Statistical sampling can be used to interrupt managed threads based on a certain mode and frequency for the purpose of collecting data about their current work.
One common use case for this functionality, usually referred to as call sampling, is to collect a backtrace from every thread when a sampling hit event arrives. This data can then be compiled into a report indicating where a program spends most of its time.
mono_profiler_enable_sampling
Enables the sampling thread. Users must call this function if they intend
to use statistical sampling; mono_profiler_set_sample_mode
will have no
effect if this function has not been called. The first profiler to call this
function will get ownership over sampling settings (mode and frequency) so
that no other profiler can change those settings. Returns
if the
sampling thread was enabled, or TRUE
if the function was called too late
for this to be possible.
FALSE
Note that mono_profiler_set_sample_mode
must still be called with a mode
other than MONO_PROFILER_SAMPLE_MODE_NONE
to actually start sampling.
This function is not async safe.
This function may only be called from a profiler's init function or prior to running managed code.
mono_profiler_set_sample_mode
Sets the sampling mode and frequency (in Hz). freq must be a positive
number. If the calling profiler has ownership over sampling settings, the
settings will be changed and this function will return
; otherwise,
it returns TRUE
without changing any settings.
FALSE
This function is async safe.
mono_profiler_get_sample_mode
Retrieves the current sampling mode and/or frequency (in Hz). Returns
if the calling profiler is allowed to change the sampling settings;
otherwise, TRUE
.
FALSE
This function is async safe.
A callback must be registered to receive sample hit events. Please see the Callback Registration section below.
Profilers can be notified about all GC allocations performed by a program or the Mono runtime.
mono_profiler_enable_allocations
Enables instrumentation of GC allocations. This is necessary so that managed
allocators can be instrumented with a call into the profiler API.
Allocations will not be reported unless this function is called. Returns
if allocation instrumentation was enabled, or TRUE
if the
function was called too late for this to be possible.
FALSE
This function is not async safe.
This function may only be called from a profiler's init function or prior to running managed code.
A callback must be registered to receive allocation events. Please see the Callback Registration section below.
The JIT compiler supports instrumenting managed method entry and exit points so that a profiler callback will be invoked.
While such callbacks by themselves have traditionally only been useful for call count profiling and the like, Mono gives these callbacks access to the arguments, locals, and return value of instrumented methods (together referred to as the 'call context'). This enables many profiling scenarios that would otherwise have required explicit hooks in the base class libraries.
mono_profiler_set_call_instrumentation_filter_callback
Sets a call instrumentation filter function. The profiler API will invoke
filter functions from all installed profilers. If any of them return flags
other than MONO_PROFILER_CALL_INSTRUMENTATION_NONE
, then the given method
will be instrumented as requested. All filters are guaranteed to be called
at least once per method, even if earlier filters have already specified all
flags.
Note that filter functions must be installed before a method is compiled in
order to have any effect, i.e. a filter should be registered in a profiler's
init function or prior to running managed code (if embedding). Also, to
instrument a method that's going to be AOT-compiled, a filter must be
installed at AOT time. This can be done in exactly the same way as one would
normally, i.e. by passing the --profile
option on the command line, by
calling mono_profiler_load
, or simply by using the profiler API as an
embedder.
Indiscriminate method instrumentation is extremely heavy and will slow down most applications to a crawl. Users should consider sampling as a possible alternative to such heavy-handed instrumentation.
This function is async safe.
mono_profiler_enable_call_context_introspection
Enables support for retrieving stack frame data from a call context. At the
moment, this means enabling the debug info subsystem. If this function is not
called, it will not be possible to use the call context introspection
functions (they will simply return
. Returns NULL
)
if call context
introspection was enabled, or TRUE
if the function was called too late for
this to be possible.
FALSE
This function is not async safe.
This function may only be called from a profiler's init function or prior to running managed code.
mono_profiler_call_context_get_this
Given a valid call context from an enter/leave event, retrieves a pointer to
the this
reference for the method. Returns
if none exists (i.e.
it's a static method) or if call context introspection was not enabled.
NULL
The buffer returned by this function must be freed with
mono_profiler_call_context_free_buffer
.
Please note that a call context is only valid for the duration of the enter/leave callback it was passed to.
This function is not async safe.
mono_profiler_call_context_get_argument
Given a valid call context from an enter/leave event, retrieves a pointer to
the method argument at the given position. Returns
if position is
out of bounds or if call context introspection was not enabled.
NULL
The buffer returned by this function must be freed with
mono_profiler_call_context_free_buffer
.
Please note that a call context is only valid for the duration of the enter/leave callback it was passed to.
This function is not async safe.
mono_profiler_call_context_get_local
Given a valid call context from an enter/leave event, retrieves a pointer to
the local variable at the given position. Returns
if position is
out of bounds or if call context introspection was not enabled.
NULL
The buffer returned by this function must be freed with
mono_profiler_call_context_free_buffer
.
Please note that a call context is only valid for the duration of the enter/leave callback it was passed to.
This function is not async safe.
mono_profiler_call_context_get_result
Given a valid call context from an enter/leave event, retrieves a pointer to
return value of a method. Returns
if the method has no return value
(i.e. it returns NULL
void)
, if the leave event was the result of a tail call,
if the function is called on a context from an enter event, or if call
context introspection was not enabled.
The buffer returned by this function must be freed with
mono_profiler_call_context_free_buffer
.
Please note that a call context is only valid for the duration of the enter/leave callback it was passed to.
This function is not async safe.
mono_profiler_call_context_free_buffer
Frees a buffer returned by one of the call context introspection functions.
Passing a
value for buffer is allowed, which makes this function
a no-op.
NULL
This function is not async safe.
Callbacks must be registered to receive method entry and exit events. Please see the Callback Registration section below.
In addition to the above functions, there's a large set of
functions for installing generic profiler event callbacks. These
are generated from C macros and so are not documented here.
Please refer to the mono/metadata/profiler.h
and
mono/metadata/profiler-events.h
headers for a full
listing of these.
Callback registration functions are all async safe and can be safely invoked from multiple threads at the same time, with the caveat that altering a registered callback from one thread will not immediately affect another thread that is already invoking the current callback.
The profiler API does not have the same API stability garantees that the rest of the Mono embedding API does. While a breaking change to the profiler API is extremely rare, it has happened in the past when changing the API in a backwards compatible way was deemed to be too much work for too little gain.
Therefore, developers of profiler modules may rarely need to update their code to work with new versions of the profiler API.
Developers who wish to support older versions of the API can
perform a compile time check of the
MONO_PROFILER_API_VERSION
macro and maintain code
for both old and new versions.
To aid with transitioning to a new version of the profiler API, the Mono runtime will detect and reject loading profiler