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Hakase
2019-10-17 23:54:38 +09:00
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doc/man3/ASYNC_start_job.pod
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@@ -27,40 +27,40 @@ ASYNC_get_current_job, ASYNC_block_pause, ASYNC_unblock_pause, ASYNC_is_capable
=head1 DESCRIPTION
OpenSSL implements asynchronous capabilities through an ASYNC_JOB. This
OpenSSL implements asynchronous capabilities through an B<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. If the user
application is multi-threaded, then ASYNC_init_thread() may be called for each
thread that will initiate asynchronous jobs. Before
The creation of an B<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. If the
user application is multi-threaded, then ASYNC_init_thread() may be called for
each thread that will initiate asynchronous jobs. Before
user code exits per-thread resources need to be cleaned up. This will normally
occur automatically (see L<OPENSSL_init_crypto(3)>) but may be explicitly
initiated by 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.
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).
The I<max_size> argument limits the number of B<ASYNC_JOB>s that will be held in
the pool. If I<max_size> is set to 0 then no upper limit is set. When an
B<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 B<ASYNC_JOB>s managed by
the pool does not exceed I<max_size>. When the pool is first initialised
I<init_size> B<ASYNC_JOB>s 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 I<max_size> of 0 (no upper limit) and an I<init_size> of 0 (no
B<ASYNC_JOB>s created up front).
An asynchronous job is started by calling the ASYNC_start_job() function.
Initially B<*job> should be NULL. B<ctx> should point to an ASYNC_WAIT_CTX
object created through the L<ASYNC_WAIT_CTX_new(3)> function. B<ret> should
Initially I<*job> should be NULL. I<ctx> should point to an B<ASYNC_WAIT_CTX>
object created through the L<ASYNC_WAIT_CTX_new(3)> function. I<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.
be stored on completion of the job. I<func> represents the function that should
be started asynchronously. The data pointed to by I<args> and of size I<size>
will be copied and then passed as an argument to I<func> when the job starts.
ASYNC_start_job will return one of the following values:
=over 4
@@ -78,47 +78,47 @@ 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
ASYNC_pause_job() below). A handle to the job is placed in I<*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.
a job call ASYNC_start_job() again passing the job handle in I<*job>. The
I<func>, I<args> and I<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>.
The job completed. I<*job> will be NULL and the return value from I<func> will
be placed in I<*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.
a pointer to the currently executing B<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
application with B<ASYNC_PAUSE> returned from the ASYNC_start_job() call. A
subsequent call to ASYNC_start_job passing in the relevant B<ASYNC_JOB> in the
I<*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.
ASYNC_get_wait_ctx() can be used to get a pointer to the ASYNC_WAIT_CTX
for the B<job>. ASYNC_WAIT_CTXs contain two different ways to notify
ASYNC_get_wait_ctx() can be used to get a pointer to the B<ASYNC_WAIT_CTX>
for the I<job>. B<ASYNC_WAIT_CTX>s contain two different ways to notify
applications that a job is ready to be resumed. One is a "wait" file
descriptor, and the other is a "callback" mechanism.
The "wait" file descriptor associated with ASYNC_WAIT_CTX is used for
The "wait" file descriptor associated with B<ASYNC_WAIT_CTX> is used for
applications to 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). If no file descriptor is made available then
an application will have to periodically "poll" the job by attempting to restart
it to see if it is ready to continue.
ASYNC_WAIT_CTXs also have a "callback" mechanism to notify applications. The
B<ASYNC_WAIT_CTX>s also have a "callback" mechanism to notify applications. The
callback is set by an application, and it will be automatically called when an
engine completes a cryptography operation, so that the application can resume
the paused work flow without polling. An engine could be written to look whether
@@ -134,10 +134,10 @@ 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 re-enable 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 acquires a lock. It then calls some cryptographic function which
to avoid deadlock scenarios. For example during the execution of an B<ASYNC_JOB>
an application acquires 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 acquire the same lock before
the B<ASYNC_JOB>. If that code then attempts to acquire the same lock before
resuming the original job then a deadlock can occur. By calling
ASYNC_block_pause() immediately after acquiring the lock and
ASYNC_unblock_pause() immediately before releasing it then this situation cannot
@@ -150,17 +150,17 @@ can be used to detect whether the current platform is async capable or not.
ASYNC_init_thread returns 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_start_job returns one of B<ASYNC_ERR>, B<ASYNC_NO_JOBS>, B<ASYNC_PAUSE> or
B<ASYNC_FINISH> as described above.
ASYNC_pause_job returns 0 if an error occurred 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.
not within the context of an B<ASYNC_JOB> then this is counted as success so 1
is returned.
ASYNC_get_current_job returns a pointer to the currently executing ASYNC_JOB or
NULL if not within the context of a job.
ASYNC_get_current_job returns a pointer to the currently executing B<ASYNC_JOB>
or NULL if not within the context of a job.
ASYNC_get_wait_ctx() returns a pointer to the ASYNC_WAIT_CTX for the job.
ASYNC_get_wait_ctx() returns a pointer to the B<ASYNC_WAIT_CTX> for the job.
ASYNC_is_capable() returns 1 if the current platform is async capable or 0
otherwise.