5. Extrae API¶

There are two levels of the API in the Extrae instrumentation package. Basic API refers to the basic functionality provided and includes emitting events, source code tracking, changing instrumentation mode and so. Extended API is an experimental addition to provide several of the basic API within single and powerful calls using specific data structures.

5.1. Basic API¶

The following routines are defined in $EXTRAE_HOME/include/extrae.h These routines are intended to be called by C/C++ programs. The instrumentation package also provides bindings for Fortran applications. The Fortran API bindings have the same name as the C API but honoring the Fortran compiler function name mangling scheme. To use the API in Fortran applications use the module provided in $EXTRAE_HOME/include/extrae_module.f90 by using the Fortran use clause. This module has to be compiled beforehand with the same compiler as the program being instrumented, with the following command:

make -f ${EXTRAE_HOME}/include/Makefile.extrae_module

void Extrae_get_version (unsigned *major, unsigned *minor, unsigned *revision)

Returns the version of the underlying Extrae package. Although an application may be compiled to a specific Extrae library, by using the appropriate shared library commands, the application may use a different Extrae library.

void Extrae_init (void)

Initializes the tracing library.

This routine is called automatically in different circumstances, which include:
- Call to MPI_Init when the appropriate instrumentation library is linked or preload with the application.
- Usage of the DynInst launcher.
- If either the libseqtrace.so, libomptrace.so or libpttrace.so are linked dynamically or preloaded with the application.
No major problems should occur if the library is initialized twice, only a warning appears in the terminal output noticing the intent of double initialization.

extrae_init_type_t Extrae_is_initialized (void)

This routine tells whether the instrumentation has been initialized, and if so, also which mechanism was the first to initialize it (regular API or MPI initialization).

void Extrae_fini (void)

Finalizes the tracing library and dumps the intermediate tracing buffers onto disk.

void Extrae_event (extrae_type_t type, extrae_value_t value)

Adds a single timestamped event into the tracefile.

Some common uses of events are:
- Identify loop iterations (or any code block):
  
  Given a loop, the user can set a unique type for the loop and a value related to the iterator value of the loop. For example:
```
for (i = 1; i <= MAX_ITERS; i++)
{
  Extrae_event (1000, i);
  [original loop code]
  Extrae_event (1000, 0);
}
```
  The last added call to Extrae_event marks the end of the loop setting the event value to 0, which facilitates the analysis with Paraver.
- Identify user routines:
  
  Choosing a constant type (6000019 in this example) and different values for different routines (set to 0 to mark a “leave” event).
```
void routine1 (void)
{
  Extrae_event (6000019, 1);
  [routine 1 code]
  Extrae_event (6000019, 0);
}

void routine2 (void)
{
  Extrae_event (6000019, 2);
  [routine 2 code]
  Extrae_event (6000019, 0);
}
```
- Identify any point in the application using a unique combination of type and value.

void Extrae_nevent (unsigned count, extrae_type_t *types, extrae_value_t *values)

Allows the user to place count events with the same timestamp at the given position.

void Extrae_counters (void)

Emits the value of the active hardware counters set. See chapter Extrae XML configuration file for further information.

void Extrae_eventandcounters (extrae_type_t event, extrae_value_t value)

This routine lets the user add an event and obtain the performance counters with one call and a single timestamp.

void Extrae_neventandcounters (unsigned count, extrae_type_t *types, extrae_value_t *values)

This routine lets the user add several events and obtain the performance counters with one call and a single timestamp.

void Extrae_define_event_type (extrae_type_t *type, char *description, unsigned *nvalues, extrae_value_t *values, char **description_values)

This routine adds to the Paraver Configuration File human readable information regarding type type and its values values. If no values need to be decribed set nvalues to 0 and also set values and description_values to NULL.

void Extrae_shutdown (void)

Turns off the instrumentation.

void Extrae_restart (void)

Turns on the instrumentation.

void Extrae_previous_hwc_set (void)

Makes the previous hardware counter set defined in the XML file to be the active set (see section XML Section: MPI for further information).

void Extrae_next_hwc_set (void)

Makes the following hardware counter set defined in the XML file to be the active set (see section XML Section: MPI for further information).

void Extrae_set_tracing_tasks (int from, int to)

Allows the user to choose from which tasks (not threads!) store information in the tracefile.

void Extrae_set_options (int options)

Permits configuring several tracing options at runtime. The options parameter has to be a bitwise or combination of the following options, depending on the user’s needs:
- EXTRAE_CALLER_OPTION
  
  Dumps caller information at each entry or exit point of the MPI routines. Caller levels need to be configured at XML (see chapter Extrae XML configuration file).
- EXTRAE_HWC_OPTION
  
  Activates hardware counter gathering.
- EXTRAE_MPI_OPTION
  
  Activates tracing of MPI calls.
- EXTRAE_MPI_HWC_OPTION
  
  Activates hardware counter gathering in MPI routines.
- EXTRAE_OMP_OPTION
  
  Activates tracing of OpenMP runtime or outlined routines.
- EXTRAE_OMP_HWC_OPTION
  
  Activates hardware counter gathering in OpenMP runtime or outlined routines.
- EXTRAE_UF_HWC_OPTION
  
  Activates hardware counter gathering in the user functions.
- EXTRAE_PTHREAD_OPTION
  
  Activates pthreads instrumentation
- EXTRAE_PTHREAD_HWC_OPTION
  
  Activates hardware counters gathering in pthread routines
- EXTRAE_SAMPLING_OPTION
  
  Activates instrumentation using time-based sampling

void Extrae_network_counters (void)

Emits the value of the network counters if the system has this capability. (Only available for systems with Myrinet GM/MX networks).

void Extrae_network_routes (int task)

Emits the network routes for an specific task. (Only available for systems with Myrinet GM/MX networks.

unsigned long long Extrae_user_function (unsigned enter)

Emits an event into the tracefile which references the source code (data includes: source line number, file name and function name). If enter is 0 it marks an end (i.e., leaving the function), otherwise it marks the beginning of the routine. The user must be careful to place the call of this routine in places where the code is always executed, being careful not to place them inside if and return statements. The function returns the address of the reference.
```
void routine1 (void)
{
  Extrae_user_function (1);
  [routine 1 code]
  Extrae_user_function (0);
}

void routine2 (void)
{
  Extrae_user_function (1);
  [routine 2 code]
  Extrae_user_function (0);
}
```
In order to gather performance counters during the execution of these calls, the user-functions tag and its counters have to be both enabled int section XML Section: User functions.

Warning

Note that you need to compile your application binary with debugging information (typically the -g compiler flag) in order to translate the captured addresses into valuable information such as function name, file name and line number.

unsigned long long Extrae_user_function_at_level (unsigned enter, unsigned lvl)

Same as Extrae_user_function but allows the specification of callstack levels to skip.

void Extrae_flush (void)

Forces the calling thread to write the events stored in the tracing buffers to disk.

5.2. Extended API¶

Warning

This API is in experimental stage and it is only available in C. Use it at your own risk!

The extended API makes use of two special structures located in $PREFIX/include/extrae_types.h. The structures are extrae_UserCommunication and extrae_CombinedEvents. The former is intended to encode an event that will be converted into a Paraver communication when its partner equivalent event has found. The latter is used to generate events containing multiple kinds of information at the same time.

struct extrae_UserCommunication
{
  extrae_user_communication_types_t type;
  extrae_comm_tag_t tag;
  unsigned size; /* size_t? */
  extrae_comm_partner_t partner;
  extrae_comm_id_t id;
};

The structure extrae_UserCommunication contains the following fields:

type Available options are:
- EXTRAE_USER_SEND, if this event represents a send point.
- EXTRAE_USER_RECV, if this event represents a receive point.
tag The tag information in the communication record.
size The size information in the communication record.
partner The partner of this communication (receive if this is a send or send if this is a receive). Partners (ranging from 0 to N-1) are considered across tasks whereas all threads share a single communication queue. Special value ‘-1’ means the partner is the same process (i.e. communication between threads).
id An identifier that is used to match communications between partners.

struct extrae_CombinedEvents
{
  /* These are used as boolean values */
  int HardwareCounters;
  int Callers;
  int UserFunction;
  /* These are intended for N events */
  unsigned nEvents;
  extrae_type_t *Types;
  extrae_value_t *Values;
  /* These are intended for user communication records */
  unsigned nCommunications;
  extrae_user_communication_t *Communications;
};

The structure extrae_CombinedEvents contains the following fields:

HardwareCounters Set to non-zero if this event has to gather hardware performance counters.
Callers Set to non-zero if this event has to emit callstack information.
UserFunction Available options are:
- EXTRAE_USER_FUNCTION_NONE, if this event should not provide information about user routines.
- EXTRAE_USER_FUNCTION_ENTER, if this event represents the starting point of a user routine.
- EXTRAE_USER_FUNCTION_LEAVE, if this event represents the ending point of a user routine.
nEvents Set the number of events given in the Types and Values fields.
Types A pointer containing nEvents type that will be stored in the trace.
Values A pointer containing nEvents values that will be stored in the trace.
nCommunications Set the number of communications given in the Communications field.
Communications A pointer to extrae_UserCommunication structures containing nCommunications elements that represent the involved communications.

The extended API contains the following routines:

void Extrae_init_UserCommunication (struct extrae_UserCommunication *)

Use this routine to initialize an extrae_UserCommunication structure.
void Extrae_init_CombinedEvents (struct extrae_CombinedEvents *)

Use this routine to initialize an extrae_CombinedEvents structure.
void Extrae_emit_CombinedEvents (struct extrae_CombinedEvents *)

Use this routine to emit to the tracefile the events set in the extrae_CombinedEvents given.
void Extrae_resume_virtual_thread (unsigned vthread)

This routine changes the thread identifier so as to be vthread in the final tracefile. Improper use of this routine may result in corrupt tracefiles.
void Extrae_suspend_virtual_thread (void)

This routine recovers the original thread identifier (given by routines like pthread_self or omp_get_thread_num, for instance).
void Extrae_register_codelocation_type (extrae_type_t t1, extrae_type_t t2, const char* s1, const char *s2)

Registers type t2 to reference user source code location by using its address. During the merge phase the mpi2prv command will assign type t1 to the event type that references the user function and to the event t2 to the event that references the file name and line location. The strings s1 and s2 refers, respectively, to the description of t1 and t2
void Extrae_register_function_address (void *ptr, const char *funcname, const char *modname, unsigned line)

By default, the mpi2prv process uses the binary debugging information to translate program addresses into information that contains function name, the module name and line. The Extrae_register_function_address allows providing such information by hand during the execution of the instrumented application. This function must provide the function name (funcname), module name (modname) and line number for a given address.
void Extrae_register_stacked_type (extrae_type_t type)

Registers which event types are required to be managed in a stack way whenever void Extrae_resume_virtual_thread or void Extrae_suspend_virtual_thread are called.
void Extrae_set_threadid_function (unsigned (*threadid_function)(void))

Defines the routine that will be used as a thread identifier inside the tracing facility.
void Extrae_set_numthreads_function (unsigned (*numthreads_function)(void))

Defines the routine that will count all the executing threads inside the tracing facility.
void Extrae_set_taskid_function (unsigned (*taskid_function)(void))

Defines the routine that will be used as a task identifier inside the tracing facility.
void Extrae_set_numtasks_function (unsigned (*numtasks_function)(void))

Defines the routine that will count all the executing tasks inside the tracing facility.
void Extrae_set_barrier_tasks_function (void (*barriertasks_function)(void))

Establishes the barrier routine among tasks. It is needed for synchronization purposes.

5.3. Java bindings¶

If Java is enabled at configure time, a basic instrumentation library for serial application based on JNI bindings to Extrae will be installed. The current bindings are within the package es.bsc.cepbatools.extrae and the following bindings are provided:

void Init ();

Initializes the instrumentation package.
void Fini ();

Finalizes the instrumentation package.
void Event (int type, long value);

Emits one event into the trace-file with the given pair type-value.
void Eventandcounters (int type, long value);

Emits one event into the trace-file with the given pair type-value as well as read the performance counters.
void nEvent (int types[], long values[]);

Emits a set of pair type-value at the same timestamp. Note that both arrays must be the same length to proceed correctly, otherwise the call ignores the call.
void nEventandcounters (int types[], long values[]);

Emits a set of pair type-value at the same timestamp as well as read the performance counters. Note that both arrays must be the same length to proceed correctly, otherwise the call ignores the call.
void defineEventType (int type, String description, long[] values, String[] descriptionValues);

Adds a description for a given event type (through type and description parameters). If the array values is non-null, then the array descriptionValues should be the an array of the same length and each entry should be a string describing each of the values given in values.
void SetOptions (int options);

This API call changes the behavior of the instrumentation package but none of the options currently apply to the Java instrumentation.
void Shutdown();

Disables the instrumentation until the next call to Restart().
void Restart();

Resumes the instrumentation from the previous Shutdown() call.

5.3.1. Advanced Java Bindings¶

Since Extrae does not have features to automatically discover the thread identifier of the threads that run within the virtual machine, there are some calls that allows to do this manually.

These calls are, however, intended for expert users and should be avoided whenever possible because their behavior may be highly modified, or even removed, in future releases.

SetTaskID (int id);

Tells Extrae that this process should be considered as task with identifier id. Use this call before invoking Init().
SetNumTasks (int num);

Instructs Extrae to allocate the structures for num processes. Use this call before invoking Init().
SetThreadID (int id);

Instructs Extrae that this thread should be considered as thread with identifier id.
SetNumThreads (int num);

Tells Extrae that there are num threads active within this process. Use this call before invoking Init().
Comm (boolean send, int tag, int size, int partner, long id);

Allows generating communications between two processes. The call emits one of the two-point communication part, so it is necessary to invoke it from both the sender and the receiver part. The send parameter determines whether this call will act as send or receive message. The tag and size parameters are used to match the communication and their parameters can be displayed in Extrae. The partner refers to the communication partner and it is identified by its TaskID. The id is meant for matching purposes but cannot be recovered during the analysis with Paraver.

5.4. Command-line version¶

Extrae incorporates a mechanism to generate trace-files from the command-line in a very naïve way in order to instrument executions driven by shell-scripted applications.

The command-line binary is installed in ${EXTRAE_HOME}/bin/extrae-cmd and supports the following commands:

init <TASKID> <THREADS>

This command initializes the tracing on the node that executed the command. The initialization command receives two parameters (TASKID, THREADS). The TASKID parameter gives an task identifier to the following forthcoming events. The THREADS parameter indicates how many threads should the task contain.
emit <THREAD-SLOT> <TYPE> <VALUE>

This command emits an event with the pair TYPE, VALUE into the the thread THREAD at the timestamp when the command is invoked.
fini

This command finalizes the instrumentation using the command-line version. Note that this finalization does not automatically call the merge process (mpi2prv).

Warning

To use these commands, do not export neither EXTRAE_ON nor EXTRAE_CONFIG_FILE, otherwise the behavior of these commands is undefined.

The initialization can be executed only once per node, so if you want to represent multiple tasks you need different tasks.

5. Extrae API¶

5.1. Basic API¶

5.2. Extended API¶

5.3. Java bindings¶

5.3.1. Advanced Java Bindings¶

5.4. Command-line version¶

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