e9b7724687
I tried hard to keep the lines at 80 characters or less, but in a few cases I had to punt and just indented the subsequent lines by 4 spaces. A few well-placed typedefs for callback functions would really help, but these would be part of the API, so that's probably for later. I also took the liberty of inserting empty lines in overlong blocks to provide some visual space. Reviewed-by: Rich Salz <rsalz@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/1956)
331 lines
12 KiB
Text
331 lines
12 KiB
Text
=pod
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=head1 NAME
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ASYNC_get_wait_ctx,
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ASYNC_init_thread, ASYNC_cleanup_thread, ASYNC_start_job, ASYNC_pause_job,
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ASYNC_get_current_job, ASYNC_block_pause, ASYNC_unblock_pause, ASYNC_is_capable
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- asynchronous job management functions
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=head1 SYNOPSIS
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#include <openssl/async.h>
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int ASYNC_init_thread(size_t max_size, size_t init_size);
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void ASYNC_cleanup_thread(void);
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int ASYNC_start_job(ASYNC_JOB **job, ASYNC_WAIT_CTX *ctx, int *ret,
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int (*func)(void *), void *args, size_t size);
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int ASYNC_pause_job(void);
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ASYNC_JOB *ASYNC_get_current_job(void);
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ASYNC_WAIT_CTX *ASYNC_get_wait_ctx(ASYNC_JOB *job);
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void ASYNC_block_pause(void);
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void ASYNC_unblock_pause(void);
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int ASYNC_is_capable(void);
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=head1 DESCRIPTION
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OpenSSL implements asynchronous capabilities through an ASYNC_JOB. This
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represents code that can be started and executes until some event occurs. At
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that point the code can be paused and control returns to user code until some
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subsequent event indicates that the job can be resumed.
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The creation of an ASYNC_JOB is a relatively expensive operation. Therefore, for
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efficiency reasons, jobs can be created up front and reused many times. They are
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held in a pool until they are needed, at which point they are removed from the
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pool, used, and then returned to the pool when the job completes. If the user
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application is multi-threaded, then ASYNC_init_thread() may be called for each
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thread that will initiate asynchronous jobs. Before
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user code exits per-thread resources need to be cleaned up. This will normally
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occur automatically (see L<OPENSSL_init_crypto(3)>) but may be explicitly
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initiated by using ASYNC_cleanup_thread(). No asynchronous jobs must be
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outstanding for the thread when ASYNC_cleanup_thread() is called. Failing to
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ensure this will result in memory leaks.
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The B<max_size> argument limits the number of ASYNC_JOBs that will be held in
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the pool. If B<max_size> is set to 0 then no upper limit is set. When an
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ASYNC_JOB is needed but there are none available in the pool already then one
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will be automatically created, as long as the total of ASYNC_JOBs managed by the
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pool does not exceed B<max_size>. When the pool is first initialised
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B<init_size> ASYNC_JOBs will be created immediately. If ASYNC_init_thread() is
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not called before the pool is first used then it will be called automatically
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with a B<max_size> of 0 (no upper limit) and an B<init_size> of 0 (no ASYNC_JOBs
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created up front).
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An asynchronous job is started by calling the ASYNC_start_job() function.
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Initially B<*job> should be NULL. B<ctx> should point to an ASYNC_WAIT_CTX
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object created through the L<ASYNC_WAIT_CTX_new(3)> function. B<ret> should
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point to a location where the return value of the asynchronous function should
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be stored on completion of the job. B<func> represents the function that should
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be started asynchronously. The data pointed to by B<args> and of size B<size>
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will be copied and then passed as an argument to B<func> when the job starts.
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ASYNC_start_job will return one of the following values:
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=over 4
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=item B<ASYNC_ERR>
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An error occurred trying to start the job. Check the OpenSSL error queue (e.g.
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see L<ERR_print_errors(3)>) for more details.
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=item B<ASYNC_NO_JOBS>
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There are no jobs currently available in the pool. This call can be retried
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again at a later time.
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=item B<ASYNC_PAUSE>
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The job was successfully started but was "paused" before it completed (see
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ASYNC_pause_job() below). A handle to the job is placed in B<*job>. Other work
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can be performed (if desired) and the job restarted at a later time. To restart
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a job call ASYNC_start_job() again passing the job handle in B<*job>. The
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B<func>, B<args> and B<size> parameters will be ignored when restarting a job.
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When restarting a job ASYNC_start_job() B<must> be called from the same thread
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that the job was originally started from.
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=item B<ASYNC_FINISH>
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The job completed. B<*job> will be NULL and the return value from B<func> will
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be placed in B<*ret>.
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=back
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At any one time there can be a maximum of one job actively running per thread
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(you can have many that are paused). ASYNC_get_current_job() can be used to get
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a pointer to the currently executing ASYNC_JOB. If no job is currently executing
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then this will return NULL.
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If executing within the context of a job (i.e. having been called directly or
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indirectly by the function "func" passed as an argument to ASYNC_start_job())
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then ASYNC_pause_job() will immediately return control to the calling
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application with ASYNC_PAUSE returned from the ASYNC_start_job() call. A
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subsequent call to ASYNC_start_job passing in the relevant ASYNC_JOB in the
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B<*job> parameter will resume execution from the ASYNC_pause_job() call. If
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ASYNC_pause_job() is called whilst not within the context of a job then no
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action is taken and ASYNC_pause_job() returns immediately.
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ASYNC_get_wait_ctx() can be used to get a pointer to the ASYNC_WAIT_CTX
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for the B<job>. ASYNC_WAIT_CTXs can have a "wait" file descriptor associated
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with them. Applications can wait for the file descriptor to be ready for "read"
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using a system function call such as select or poll (being ready for "read"
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indicates that the job should be resumed). If no file descriptor is made
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available then an application will have to periodically "poll" the job by
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attempting to restart it to see if it is ready to continue.
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An example of typical usage might be an async capable engine. User code would
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initiate cryptographic operations. The engine would initiate those operations
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asynchronously and then call L<ASYNC_WAIT_CTX_set_wait_fd(3)> followed by
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ASYNC_pause_job() to return control to the user code. The user code can then
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perform other tasks or wait for the job to be ready by calling "select" or other
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similar function on the wait file descriptor. The engine can signal to the user
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code that the job should be resumed by making the wait file descriptor
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"readable". Once resumed the engine should clear the wake signal on the wait
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file descriptor.
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The ASYNC_block_pause() function will prevent the currently active job from
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pausing. The block will remain in place until a subsequent call to
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ASYNC_unblock_pause(). These functions can be nested, e.g. if you call
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ASYNC_block_pause() twice then you must call ASYNC_unblock_pause() twice in
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order to re-enable pausing. If these functions are called while there is no
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currently active job then they have no effect. This functionality can be useful
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to avoid deadlock scenarios. For example during the execution of an ASYNC_JOB an
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application acquires a lock. It then calls some cryptographic function which
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invokes ASYNC_pause_job(). This returns control back to the code that created
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the ASYNC_JOB. If that code then attempts to acquire the same lock before
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resuming the original job then a deadlock can occur. By calling
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ASYNC_block_pause() immediately after acquiring the lock and
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ASYNC_unblock_pause() immediately before releasing it then this situation cannot
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occur.
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Some platforms cannot support async operations. The ASYNC_is_capable() function
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can be used to detect whether the current platform is async capable or not.
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=head1 RETURN VALUES
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ASYNC_init_thread returns 1 on success or 0 otherwise.
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ASYNC_start_job returns one of ASYNC_ERR, ASYNC_NO_JOBS, ASYNC_PAUSE or
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ASYNC_FINISH as described above.
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ASYNC_pause_job returns 0 if an error occurred or 1 on success. If called when
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not within the context of an ASYNC_JOB then this is counted as success so 1 is
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returned.
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ASYNC_get_current_job returns a pointer to the currently executing ASYNC_JOB or
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NULL if not within the context of a job.
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ASYNC_get_wait_ctx() returns a pointer to the ASYNC_WAIT_CTX for the job.
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ASYNC_is_capable() returns 1 if the current platform is async capable or 0
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otherwise.
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=head1 NOTES
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On Windows platforms the openssl/async.h header is dependent on some
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of the types customarily made available by including windows.h. The
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application developer is likely to require control over when the latter
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is included, commonly as one of the first included headers. Therefore
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it is defined as an application developer's responsibility to include
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windows.h prior to async.h.
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=head1 EXAMPLE
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The following example demonstrates how to use most of the core async APIs:
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#ifdef _WIN32
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# include <windows.h>
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#endif
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#include <stdio.h>
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#include <unistd.h>
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#include <openssl/async.h>
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#include <openssl/crypto.h>
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int unique = 0;
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void cleanup(ASYNC_WAIT_CTX *ctx, const void *key, OSSL_ASYNC_FD r, void *vw)
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{
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OSSL_ASYNC_FD *w = (OSSL_ASYNC_FD *)vw;
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close(r);
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close(*w);
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OPENSSL_free(w);
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}
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int jobfunc(void *arg)
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{
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ASYNC_JOB *currjob;
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unsigned char *msg;
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int pipefds[2] = {0, 0};
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OSSL_ASYNC_FD *wptr;
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char buf = 'X';
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currjob = ASYNC_get_current_job();
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if (currjob != NULL) {
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printf("Executing within a job\n");
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} else {
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printf("Not executing within a job - should not happen\n");
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return 0;
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}
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msg = (unsigned char *)arg;
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printf("Passed in message is: %s\n", msg);
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if (pipe(pipefds) != 0) {
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printf("Failed to create pipe\n");
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return 0;
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}
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wptr = OPENSSL_malloc(sizeof(OSSL_ASYNC_FD));
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if (wptr == NULL) {
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printf("Failed to malloc\n");
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return 0;
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}
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*wptr = pipefds[1];
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ASYNC_WAIT_CTX_set_wait_fd(ASYNC_get_wait_ctx(currjob), &unique,
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pipefds[0], wptr, cleanup);
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/*
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* Normally some external event would cause this to happen at some
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* later point - but we do it here for demo purposes, i.e.
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* immediately signalling that the job is ready to be woken up after
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* we return to main via ASYNC_pause_job().
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*/
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write(pipefds[1], &buf, 1);
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/* Return control back to main */
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ASYNC_pause_job();
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/* Clear the wake signal */
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read(pipefds[0], &buf, 1);
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printf ("Resumed the job after a pause\n");
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return 1;
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}
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int main(void)
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{
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ASYNC_JOB *job = NULL;
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ASYNC_WAIT_CTX *ctx = NULL;
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int ret;
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OSSL_ASYNC_FD waitfd;
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fd_set waitfdset;
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size_t numfds;
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unsigned char msg[13] = "Hello world!";
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printf("Starting...\n");
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ctx = ASYNC_WAIT_CTX_new();
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if (ctx == NULL) {
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printf("Failed to create ASYNC_WAIT_CTX\n");
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abort();
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}
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for (;;) {
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switch (ASYNC_start_job(&job, ctx, &ret, jobfunc, msg, sizeof(msg))) {
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case ASYNC_ERR:
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case ASYNC_NO_JOBS:
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printf("An error occurred\n");
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goto end;
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case ASYNC_PAUSE:
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printf("Job was paused\n");
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break;
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case ASYNC_FINISH:
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printf("Job finished with return value %d\n", ret);
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goto end;
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}
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/* Wait for the job to be woken */
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printf("Waiting for the job to be woken up\n");
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if (!ASYNC_WAIT_CTX_get_all_fds(ctx, NULL, &numfds)
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|| numfds > 1) {
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printf("Unexpected number of fds\n");
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abort();
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}
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ASYNC_WAIT_CTX_get_all_fds(ctx, &waitfd, &numfds);
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FD_ZERO(&waitfdset);
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FD_SET(waitfd, &waitfdset);
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select(waitfd + 1, &waitfdset, NULL, NULL, NULL);
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}
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end:
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ASYNC_WAIT_CTX_free(ctx);
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printf("Finishing\n");
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return 0;
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}
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The expected output from executing the above example program is:
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Starting...
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Executing within a job
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Passed in message is: Hello world!
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Job was paused
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Waiting for the job to be woken up
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Resumed the job after a pause
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Job finished with return value 1
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Finishing
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=head1 SEE ALSO
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L<crypto(7)>, L<ERR_print_errors(3)>
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=head1 HISTORY
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ASYNC_init_thread, ASYNC_cleanup_thread,
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ASYNC_start_job, ASYNC_pause_job, ASYNC_get_current_job, ASYNC_get_wait_ctx(),
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ASYNC_block_pause(), ASYNC_unblock_pause() and ASYNC_is_capable() were first
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added to OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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