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author | Matt Caswell <matt@openssl.org> | 2015-09-23 13:51:58 +0100 |
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committer | Matt Caswell <matt@openssl.org> | 2015-11-20 23:34:34 +0000 |
commit | c00793da995b6e2d52ac4423dc8d5a8607852ff8 (patch) | |
tree | 9f2e8ad3c24f8d833bcf696edf85bbfc7d1cd0f6 /doc/crypto | |
parent | 4f70d04593951905fa560719ae7aaa032aca14ca (diff) | |
download | openssl-c00793da995b6e2d52ac4423dc8d5a8607852ff8.tar.gz |
Document async capabilities
Reviewed-by: Rich Salz <rsalz@openssl.org>
Diffstat (limited to 'doc/crypto')
-rw-r--r-- | doc/crypto/ASYNC_start_job.pod | 242 |
1 files changed, 242 insertions, 0 deletions
diff --git a/doc/crypto/ASYNC_start_job.pod b/doc/crypto/ASYNC_start_job.pod new file mode 100644 index 0000000000..ec896340f8 --- /dev/null +++ b/doc/crypto/ASYNC_start_job.pod @@ -0,0 +1,242 @@ +=pod + +=head1 NAME + +ASYNC_init_pool, ASYNC_free_pool, ASYNC_start_job, ASYNC_pause_job, +ASYNC_in_job, ASYNC_get_wait_fd, ASYNC_get_current_job, ASYNC_wake, +ASYNC_clear_wake - asynchronous job management functions + +=head1 SYNOPSIS + + #include <openssl/async.h> + + int ASYNC_init_pool(size_t max_size, size_t init_size); + void ASYNC_free_pool(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); + +=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_pool(). If the user application is multi-threaded, then this should +be done for each thread that will initiate asynchronous jobs. Before user code +exits it should free the pool up (for each thread where a pool was initialised) +using ASYNC_free_pool(). 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_pool() 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_free_pool(). + +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. + +=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 + +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 on the file descriptor using a system function call +such as select or poll. 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_wait(). Once resumed the engine would clear the wake signal by calling +ASYNC_clear_wake(). + + +=head1 RETURN VALUES + +ASYNC_init_pool 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_pause_job returns 0 if an error occured (including if called when not +within the context of an ASYNC_JOB), or 1 on success. + +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_pool(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_free_pool(); + + 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_pool, ASYNC_free_pool, 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 |