doc/crypto/ASYNC_start_job.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 ASYNC_init, ASYNC_cleanup, ASYNC_init_thread, ASYNC_cleanup_thread,
 ASYNC_start_job, ASYNC_pause_job, ASYNC_in_job, ASYNC_get_wait_fd,
 ASYNC_get_current_job, ASYNC_wake, ASYNC_clear_wake, ASYNC_block_pause,
 ASYNC_unblock_pause - asynchronous job management functions

 =head1 SYNOPSIS

  #include <openssl/async.h>

  int ASYNC_init(int init_thread, size_t max_size, size_t init_size);
  void ASYNC_cleanup(int cleanupthread);

  int ASYNC_init_thread(size_t max_size, size_t init_size);
  void ASYNC_cleanup_thread(void);

  int ASYNC_start_job(ASYNC_JOB **job, int *ret, int (*func)(void *),
                      void *args, size_t size);
  int ASYNC_pause_job(void);

  int ASYNC_get_wait_fd(ASYNC_JOB *job);
  ASYNC_JOB *ASYNC_get_current_job(void);
  void ASYNC_wake(ASYNC_JOB *job);
  void ASYNC_clear_wake(ASYNC_JOB *job);
  void ASYNC_block_pause(void);
  void ASYNC_unblock_pause(void);

 =head1 DESCRIPTION

 OpenSSL implements asynchronous capabilities through an ASYNC_JOB. This
 represents code that can be started and executes until some event occurs. At
 that point the code can be paused and control returns to user code until some
 subsequent event indicates that the job can be resumed.

 The creation of an ASYNC_JOB is a relatively expensive operation. Therefore, for
 efficiency reasons, jobs can be created up front and reused many times. They are
 held in a pool until they are needed, at which point they are removed from the
 pool, used, and then returned to the pool when the job completes. Before using
 any of the asynchronous job functions, user code should first call
 ASYNC_init(). If the user application is multi-threaded, then
 ASYNC_init_thread() should be called for each thread that will initiate
 asynchronous jobs. If the B<init_thread> parameter to ASYNC_init() is non-zero
 then ASYNC_init_thread is automatically called for the current thread. Before
 user code exits it should free up resources for each thread that was initialised
 using ASYNC_cleanup_thread(). No asynchronous jobs must be outstanding for the thread
 when ASYNC_cleanup_thread() is called. Failing to ensure this will result in memory
 leaks. Additionally an application should call ASYNC_cleanup() when all
 asynchronous work is complete across all threads. If B<cleanupthread> is
 non-zero then ASYNC_cleanup_thread() is automatically called for the current
 thread.

 The B<max_size> argument limits the number of ASYNC_JOBs that will be held in
 the pool. If B<max_size> is set to 0 then no upper limit is set. When an
 ASYNC_JOB is needed but there are none available in the pool already then one
 will be automatically created, as long as the total of ASYNC_JOBs managed by the
 pool does not exceed B<max_size>. When the pool is first initialised
 B<init_size> ASYNC_JOBs will be created immediately. If ASYNC_init_thread() is
 not called before the pool is first used then it will be called automatically
 with a B<max_size> of 0 (no upper limit) and an B<init_size> of 0 (no ASYNC_JOBs
 created up front). If a pool is created in this way it must still be cleaned up
 with an explicit call to ASYNC_cleanup_thread().

 An asynchronous job is started by calling the ASYNC_start_job() function.
 Initially B<*job> should be NULL. B<ret> should point to a location where the
 return value of the asynchronous function should be stored on completion of the
 job. B<func> represents the function that should be started asynchronously. The
 data pointed to by B<args> and of size B<size> will be copied and then passed as
 an argument to B<func> when the job starts. ASYNC_start_job will return one of
 the following values:

 =over 4

 =item B<ASYNC_ERR>

 An error occurred trying to start the job. Check the OpenSSL error queue (e.g.
 see L<ERR_print_errors(3)>) for more details.

 =item B<ASYNC_NO_JOBS>

 There are no jobs currently available in the pool. This call can be retried
 again at a later time.

 =item B<ASYNC_PAUSE>

 The job was successfully started but was "paused" before it completed (see
 ASYNC_pause_job() below). A handle to the job is placed in B<*job>. Other work
 can be performed (if desired) and the job restarted at a later time. To restart
 a job call ASYNC_start_job() again passing the job handle in B<*job>. The
 B<func>, B<args> and B<size> parameters will be ignored when restarting a job.
 When restarting a job ASYNC_start_job() B<must> be called from the same thread
 that the job was originally started from.

 =item B<ASYNC_FINISH>

 The job completed. B<*job> will be NULL and the return value from B<func> will
 be placed in B<*ret>.

 =back

 At any one time there can be a maximum of one job actively running per thread
 (you can have many that are paused). ASYNC_get_current_job() can be used to get
 a pointer to the currently executing ASYNC_JOB. If no job is currently executing
 then this will return NULL.

 If executing within the context of a job (i.e. having been called directly or
 indirectly by the function "func" passed as an argument to ASYNC_start_job())
 then ASYNC_pause_job() will immediately return control to the calling
 application with ASYNC_PAUSE returned from the ASYNC_start_job() call. A
 subsequent call to ASYNC_start_job passing in the relevant ASYNC_JOB in the
 B<*job> parameter will resume execution from the ASYNC_pause_job() call. If
 ASYNC_pause_job() is called whilst not within the context of a job then no
 action is taken and ASYNC_pause_job() returns immediately.

 Every ASYNC_JOB has a "wait" file descriptor associated with it. Calling
 ASYNC_get_wait_fd() and passing in a pointer to an ASYNC_JOB in the B<job>
 parameter will return the wait file descriptor associated with that job. This
 file descriptor can be used to signal that the job should be resumed.
 Applications can wait for the file descriptor to be ready for "read" using a
 system function call such as select or poll (being ready for "read" indicates
 that the job should be resumed). Applications can signal that a job is ready to
 resume using ASYNC_wake() or clear an existing signal using ASYNC_clear_wake().

 An example of typical usage might be an async capable engine. User code would
 initiate cryptographic operations. The engine would initiate those operations
 asynchronously and then call ASYNC_pause_job() to return control to the user
 code. The user code can then perform other tasks or wait for the job to be ready
 by calling "select" or other similar function on the wait file descriptor. The
 engine can signal to the user code that the job should be resumed using
 ASYNC_wake(). Once resumed the engine would clear the wake signal by calling
 ASYNC_clear_wake().

 The ASYNC_block_pause() function will prevent the currently active job from
 pausing. The block will remain in place until a subsequent call to
 ASYNC_unblock_pause(). These functions can be nested, e.g. if you call
 ASYNC_block_pause() twice then you must call ASYNC_unblock_pause() twice in
 order to reenable pausing. If these functions are called while there is no
 currently active job then they have no effect. This functionality can be useful
 to avoid deadlock scenarios. For example during the execution of an ASYNC_JOB an
 application aquires a lock. It then calls some cryptographic function which
 invokes ASYNC_pause_job(). This returns control back to the code that created
 the ASYNC_JOB. If that code then attempts to aquire the same lock before
 resuming the original job then a deadlock can occur. By calling
 ASYNC_block_pause() immediately after aquiring the lock and
 ASYNC_unblock_pause() immediately before releasing it then this situation cannot
 occur.

 =head1 RETURN VALUES

 ASYNC_init and ASYNC_init_thread return 1 on success or 0 otherwise.

 ASYNC_start_job returns one of ASYNC_ERR, ASYNC_NO_JOBS, ASYNC_PAUSE or
 ASYNC_FINISH as described above.

 ASYNC_pause_job returns 0 if an error occured or 1 on success. If called when
 not within the context of an ASYNC_JOB then this is counted as success so 1 is
 returned.

 ASYNC_get_wait_fd returns the "wait" file descriptor associated with the
 ASYNC_JOB provided as an argument.

 ASYNC_get_current_job returns a pointer to the currently executing ASYNC_JOB or
 NULL if not within the context of a job.

 =head1 EXAMPLE

 The following example demonstrates how to use most of the core async APIs:

  #include <stdio.h>
  #include <openssl/async.h>

  int jobfunc(void *arg)
  {
      ASYNC_JOB *currjob;
      unsigned char *msg;

      currjob = ASYNC_get_current_job();
      if (currjob != NULL) {
          printf("Executing within a job\n");
      } else {
          printf("Not executing within a job - should not happen\n");
          return 0;
      }

      msg = (unsigned char *)arg;
      printf("Passed in message is: %s\n", msg);

      /*
       * Normally some external event would cause this to happen at some
       * later point - but we do it here for demo purposes, i.e.
       * immediately signalling that the job is ready to be woken up after
       * we return to main via ASYNC_pause_job().
       */
      ASYNC_wake(currjob);

      /* Return control back to main */
      ASYNC_pause_job();

      /* Clear the wake signal */
      ASYNC_clear_wake(currjob);

      printf ("Resumed the job after a pause\n");

      return 1;
  }

  int main(void)
  {
      ASYNC_JOB *job = NULL;
      int ret, waitfd;
      fd_set waitfdset;
      unsigned char msg[13] = "Hello world!";

      /*
       * We're only expecting 1 job to be used here so we're only creating
       * a pool of 1
       */
      if (!ASYNC_init(1, 1, 1)) {
          printf("Error creating pool\n");
          goto end;
      }

      printf("Starting...\n");

      for (;;) {
          switch(ASYNC_start_job(&job, &ret, jobfunc, msg, sizeof(msg))) {
          case ASYNC_ERR:
          case ASYNC_NO_JOBS:
                  printf("An error occurred\n");
                  goto end;
          case ASYNC_PAUSE:
                  printf("Job was paused\n");
                  break;
          case ASYNC_FINISH:
                  printf("Job finished with return value %d\n", ret);
                  goto end;
          }

          /* Wait for the job to be woken */
          printf("Waiting for the job to be woken up\n");
          waitfd = ASYNC_get_wait_fd(job);
          FD_ZERO(&waitfdset);
          FD_SET(waitfd, &waitfdset);
          select(waitfd + 1, &waitfdset, NULL, NULL, NULL);
      }

  end:
      printf("Finishing\n");
      ASYNC_cleanup(1);

      return 0;
  }

 The expected output from executing the above example program is:

  Starting...
  Executing within a job
  Passed in message is: Hello world!
  Job was paused
  Waiting for the job to be woken up
  Resumed the job after a pause
  Job finished with return value 1
  Finishing

 =head1 SEE ALSO

 L<crypto(3)>, L<ERR_print_errors(3)>

 =head1 HISTORY

 ASYNC_init, ASYNC_init_thread, ASYNC_cleanup, ASYNC_cleanup_thread,
 ASYNC_start_job, ASYNC_pause_job, ASYNC_get_wait_fd, ASYNC_get_current_job,
 ASYNC_wake, ASYNC_clear_wake were first added to OpenSSL 1.1.0.

 =cut
	=pod

	=head1 NAME

	ASYNC_init, ASYNC_cleanup, ASYNC_init_thread, ASYNC_cleanup_thread,
	ASYNC_start_job, ASYNC_pause_job, ASYNC_in_job, ASYNC_get_wait_fd,
	ASYNC_get_current_job, ASYNC_wake, ASYNC_clear_wake, ASYNC_block_pause,
	ASYNC_unblock_pause - asynchronous job management functions

	=head1 SYNOPSIS

	#include <openssl/async.h>

	int ASYNC_init(int init_thread, size_t max_size, size_t init_size);
	void ASYNC_cleanup(int cleanupthread);

	int ASYNC_init_thread(size_t max_size, size_t init_size);
	void ASYNC_cleanup_thread(void);

	int ASYNC_start_job(ASYNC_JOB *job, int ret, int (func)(void ),
	void *args, size_t size);
	int ASYNC_pause_job(void);

	int ASYNC_get_wait_fd(ASYNC_JOB *job);
	ASYNC_JOB *ASYNC_get_current_job(void);
	void ASYNC_wake(ASYNC_JOB *job);
	void ASYNC_clear_wake(ASYNC_JOB *job);
	void ASYNC_block_pause(void);
	void ASYNC_unblock_pause(void);

	=head1 DESCRIPTION

	OpenSSL implements asynchronous capabilities through an ASYNC_JOB. This
	represents code that can be started and executes until some event occurs. At
	that point the code can be paused and control returns to user code until some
	subsequent event indicates that the job can be resumed.

	The creation of an ASYNC_JOB is a relatively expensive operation. Therefore, for
	efficiency reasons, jobs can be created up front and reused many times. They are
	held in a pool until they are needed, at which point they are removed from the
	pool, used, and then returned to the pool when the job completes. Before using
	any of the asynchronous job functions, user code should first call
	ASYNC_init(). If the user application is multi-threaded, then
	ASYNC_init_thread() should be called for each thread that will initiate
	asynchronous jobs. If the B<init_thread> parameter to ASYNC_init() is non-zero
	then ASYNC_init_thread is automatically called for the current thread. Before
	user code exits it should free up resources for each thread that was initialised
	using ASYNC_cleanup_thread(). No asynchronous jobs must be outstanding for the thread
	when ASYNC_cleanup_thread() is called. Failing to ensure this will result in memory
	leaks. Additionally an application should call ASYNC_cleanup() when all
	asynchronous work is complete across all threads. If B<cleanupthread> is
	non-zero then ASYNC_cleanup_thread() is automatically called for the current
	thread.

	The B<max_size> argument limits the number of ASYNC_JOBs that will be held in
	the pool. If B<max_size> is set to 0 then no upper limit is set. When an
	ASYNC_JOB is needed but there are none available in the pool already then one
	will be automatically created, as long as the total of ASYNC_JOBs managed by the
	pool does not exceed B<max_size>. When the pool is first initialised
	B<init_size> ASYNC_JOBs will be created immediately. If ASYNC_init_thread() is
	not called before the pool is first used then it will be called automatically
	with a B<max_size> of 0 (no upper limit) and an B<init_size> of 0 (no ASYNC_JOBs
	created up front). If a pool is created in this way it must still be cleaned up
	with an explicit call to ASYNC_cleanup_thread().

	An asynchronous job is started by calling the ASYNC_start_job() function.
	Initially B<*job> should be NULL. B<ret> should point to a location where the
	return value of the asynchronous function should be stored on completion of the
	job. B<func> represents the function that should be started asynchronously. The
	data pointed to by B<args> and of size B<size> will be copied and then passed as
	an argument to B<func> when the job starts. ASYNC_start_job will return one of
	the following values:

	=over 4

	=item B<ASYNC_ERR>

	An error occurred trying to start the job. Check the OpenSSL error queue (e.g.
	see L<ERR_print_errors(3)>) for more details.

	=item B<ASYNC_NO_JOBS>

	There are no jobs currently available in the pool. This call can be retried
	again at a later time.

	=item B<ASYNC_PAUSE>

	The job was successfully started but was "paused" before it completed (see
	ASYNC_pause_job() below). A handle to the job is placed in B<*job>. Other work
	can be performed (if desired) and the job restarted at a later time. To restart
	a job call ASYNC_start_job() again passing the job handle in B<*job>. The
	B<func>, B<args> and B<size> parameters will be ignored when restarting a job.
	When restarting a job ASYNC_start_job() B<must> be called from the same thread
	that the job was originally started from.

	=item B<ASYNC_FINISH>

	The job completed. B<*job> will be NULL and the return value from B<func> will
	be placed in B<*ret>.

	=back

	At any one time there can be a maximum of one job actively running per thread
	(you can have many that are paused). ASYNC_get_current_job() can be used to get
	a pointer to the currently executing ASYNC_JOB. If no job is currently executing
	then this will return NULL.

	If executing within the context of a job (i.e. having been called directly or
	indirectly by the function "func" passed as an argument to ASYNC_start_job())
	then ASYNC_pause_job() will immediately return control to the calling
	application with ASYNC_PAUSE returned from the ASYNC_start_job() call. A
	subsequent call to ASYNC_start_job passing in the relevant ASYNC_JOB in the
	B<*job> parameter will resume execution from the ASYNC_pause_job() call. If
	ASYNC_pause_job() is called whilst not within the context of a job then no
	action is taken and ASYNC_pause_job() returns immediately.

	Every ASYNC_JOB has a "wait" file descriptor associated with it. Calling
	ASYNC_get_wait_fd() and passing in a pointer to an ASYNC_JOB in the B<job>
	parameter will return the wait file descriptor associated with that job. This
	file descriptor can be used to signal that the job should be resumed.
	Applications can wait for the file descriptor to be ready for "read" using a
	system function call such as select or poll (being ready for "read" indicates
	that the job should be resumed). Applications can signal that a job is ready to
	resume using ASYNC_wake() or clear an existing signal using ASYNC_clear_wake().

	An example of typical usage might be an async capable engine. User code would
	initiate cryptographic operations. The engine would initiate those operations
	asynchronously and then call ASYNC_pause_job() to return control to the user
	code. The user code can then perform other tasks or wait for the job to be ready
	by calling "select" or other similar function on the wait file descriptor. The
	engine can signal to the user code that the job should be resumed using
	ASYNC_wake(). Once resumed the engine would clear the wake signal by calling
	ASYNC_clear_wake().

	The ASYNC_block_pause() function will prevent the currently active job from
	pausing. The block will remain in place until a subsequent call to
	ASYNC_unblock_pause(). These functions can be nested, e.g. if you call
	ASYNC_block_pause() twice then you must call ASYNC_unblock_pause() twice in
	order to reenable pausing. If these functions are called while there is no
	currently active job then they have no effect. This functionality can be useful
	to avoid deadlock scenarios. For example during the execution of an ASYNC_JOB an
	application aquires a lock. It then calls some cryptographic function which
	invokes ASYNC_pause_job(). This returns control back to the code that created
	the ASYNC_JOB. If that code then attempts to aquire the same lock before
	resuming the original job then a deadlock can occur. By calling
	ASYNC_block_pause() immediately after aquiring the lock and
	ASYNC_unblock_pause() immediately before releasing it then this situation cannot
	occur.

	=head1 RETURN VALUES

	ASYNC_init and ASYNC_init_thread return 1 on success or 0 otherwise.

	ASYNC_start_job returns one of ASYNC_ERR, ASYNC_NO_JOBS, ASYNC_PAUSE or
	ASYNC_FINISH as described above.

	ASYNC_pause_job returns 0 if an error occured or 1 on success. If called when
	not within the context of an ASYNC_JOB then this is counted as success so 1 is
	returned.

	ASYNC_get_wait_fd returns the "wait" file descriptor associated with the
	ASYNC_JOB provided as an argument.

	ASYNC_get_current_job returns a pointer to the currently executing ASYNC_JOB or
	NULL if not within the context of a job.

	=head1 EXAMPLE

	The following example demonstrates how to use most of the core async APIs:

	#include <stdio.h>
	#include <openssl/async.h>

	int jobfunc(void *arg)
	{
	ASYNC_JOB *currjob;
	unsigned char *msg;

	currjob = ASYNC_get_current_job();
	if (currjob != NULL) {
	printf("Executing within a job\n");
	} else {
	printf("Not executing within a job - should not happen\n");
	return 0;
	}

	msg = (unsigned char *)arg;
	printf("Passed in message is: %s\n", msg);

	/*
	* Normally some external event would cause this to happen at some
	* later point - but we do it here for demo purposes, i.e.
	* immediately signalling that the job is ready to be woken up after
	* we return to main via ASYNC_pause_job().
	*/
	ASYNC_wake(currjob);

	/* Return control back to main */
	ASYNC_pause_job();

	/* Clear the wake signal */
	ASYNC_clear_wake(currjob);

	printf ("Resumed the job after a pause\n");

	return 1;
	}

	int main(void)
	{
	ASYNC_JOB *job = NULL;
	int ret, waitfd;
	fd_set waitfdset;
	unsigned char msg[13] = "Hello world!";

	/*
	* We're only expecting 1 job to be used here so we're only creating
	* a pool of 1
	*/
	if (!ASYNC_init(1, 1, 1)) {
	printf("Error creating pool\n");
	goto end;
	}

	printf("Starting...\n");

	for (;;) {
	switch(ASYNC_start_job(&job, &ret, jobfunc, msg, sizeof(msg))) {
	case ASYNC_ERR:
	case ASYNC_NO_JOBS:
	printf("An error occurred\n");
	goto end;
	case ASYNC_PAUSE:
	printf("Job was paused\n");
	break;
	case ASYNC_FINISH:
	printf("Job finished with return value %d\n", ret);
	goto end;
	}

	/* Wait for the job to be woken */
	printf("Waiting for the job to be woken up\n");
	waitfd = ASYNC_get_wait_fd(job);
	FD_ZERO(&waitfdset);
	FD_SET(waitfd, &waitfdset);
	select(waitfd + 1, &waitfdset, NULL, NULL, NULL);
	}

	end:
	printf("Finishing\n");
	ASYNC_cleanup(1);

	return 0;
	}

	The expected output from executing the above example program is:

	Starting...
	Executing within a job
	Passed in message is: Hello world!
	Job was paused
	Waiting for the job to be woken up
	Resumed the job after a pause
	Job finished with return value 1
	Finishing

	=head1 SEE ALSO

	L<crypto(3)>, L<ERR_print_errors(3)>

	=head1 HISTORY

	ASYNC_init, ASYNC_init_thread, ASYNC_cleanup, ASYNC_cleanup_thread,
	ASYNC_start_job, ASYNC_pause_job, ASYNC_get_wait_fd, ASYNC_get_current_job,
	ASYNC_wake, ASYNC_clear_wake were first added to OpenSSL 1.1.0.

	=cut