ASYNC_get_wait_ctx (3)
Leading comments
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NAME
ASYNC_get_wait_ctx, ASYNC_init_thread, ASYNC_cleanup_thread, ASYNC_start_job, ASYNC_pause_job, ASYNC_get_current_job, ASYNC_block_pause, ASYNC_unblock_pause, ASYNC_is_capable - asynchronous job management functionsSYNOPSIS
#include <openssl/async.h> int ASYNC_init_thread(size_t max_size, size_t init_size); void ASYNC_cleanup_thread(void); int ASYNC_start_job(ASYNC_JOB **job, ASYNC_WAIT_CTX *ctx, int *ret, int (*func)(void *), void *args, size_t size); int ASYNC_pause_job(void); ASYNC_JOB *ASYNC_get_current_job(void); ASYNC_WAIT_CTX *ASYNC_get_wait_ctx(ASYNC_JOB *job); void ASYNC_block_pause(void); void ASYNC_unblock_pause(void); int ASYNC_is_capable(void);
DESCRIPTION
OpenSSL implements asynchronous capabilities through anThe creation of an
The max_size argument limits the number of ASYNC_JOBs that will be held in the pool. If max_size is set to 0 then no upper limit is set. When an
An asynchronous job is started by calling the ASYNC_start_job() function. Initially *job should be
- ASYNC_ERR
- An error occurred trying to start the job. Check the OpenSSL error queue (e.g. see ERR_print_errors(3)) for more details.
- ASYNC_NO_JOBS
- There are no jobs currently available in the pool. This call can be retried again at a later time.
- 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 *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 *job. The func, args and size parameters will be ignored when restarting a job. When restarting a job ASYNC_start_job() must be called from the same thread that the job was originally started from.
- ASYNC_FINISH
-
The job completed. *job will be NULLand the return value from func will be placed in *ret.
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
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_get_wait_ctx() can be used to get a pointer to the
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_WAIT_CTX_set_wait_fd(3) followed by 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 by making the wait file descriptor ``readable''. Once resumed the engine should clear the wake signal on the wait file descriptor.
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 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
Some platforms cannot support async operations. The ASYNC_is_capable() function can be used to detect whether the current platform is async capable or not.
RETURN VALUES
ASYNC_init_thread returns 1 on success or 0 otherwise.ASYNC_start_job returns one of
ASYNC_pause_job returns 0 if an error occurred or 1 on success. If called when not within the context of an
ASYNC_get_current_job returns a pointer to the currently executing
ASYNC_get_wait_ctx() returns a pointer to the
ASYNC_is_capable() returns 1 if the current platform is async capable or 0 otherwise.
NOTES
On Windows platforms the openssl/async.h header is dependent on some of the types customarily made available by including windows.h. The application developer is likely to require control over when the latter is included, commonly as one of the first included headers. Therefore it is defined as an application developer's responsibility to include windows.h prior to async.h.EXAMPLE
The following example demonstrates how to use most of the core async APIs:
#ifdef _WIN32 # include <windows.h> #endif #include <stdio.h> #include <unistd.h> #include <openssl/async.h> #include <openssl/crypto.h> int unique = 0; void cleanup(ASYNC_WAIT_CTX *ctx, const void *key, OSSL_ASYNC_FD r, void *vw) { OSSL_ASYNC_FD *w = (OSSL_ASYNC_FD *)vw; close(r); close(*w); OPENSSL_free(w); } int jobfunc(void *arg) { ASYNC_JOB *currjob; unsigned char *msg; int pipefds[2] = {0, 0}; OSSL_ASYNC_FD *wptr; char buf = 'X'; 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); if (pipe(pipefds) != 0) { printf("Failed to create pipe\n"); return 0; } wptr = OPENSSL_malloc(sizeof(OSSL_ASYNC_FD)); if (wptr == NULL) { printf("Failed to malloc\n"); return 0; } *wptr = pipefds[1]; ASYNC_WAIT_CTX_set_wait_fd(ASYNC_get_wait_ctx(currjob), &unique, pipefds[0], wptr, cleanup); /* * 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(). */ write(pipefds[1], &buf, 1); /* Return control back to main */ ASYNC_pause_job(); /* Clear the wake signal */ read(pipefds[0], &buf, 1); printf ("Resumed the job after a pause\n"); return 1; } int main(void) { ASYNC_JOB *job = NULL; ASYNC_WAIT_CTX *ctx = NULL; int ret; OSSL_ASYNC_FD waitfd; fd_set waitfdset; size_t numfds; unsigned char msg[13] = "Hello world!"; printf("Starting...\n"); ctx = ASYNC_WAIT_CTX_new(); if (ctx == NULL) { printf("Failed to create ASYNC_WAIT_CTX\n"); abort(); } for (;;) { switch(ASYNC_start_job(&job, ctx, &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"); if (!ASYNC_WAIT_CTX_get_all_fds(ctx, NULL, &numfds) || numfds > 1) { printf("Unexpected number of fds\n"); abort(); } ASYNC_WAIT_CTX_get_all_fds(ctx, &waitfd, &numfds); FD_ZERO(&waitfdset); FD_SET(waitfd, &waitfdset); select(waitfd + 1, &waitfdset, NULL, NULL, NULL); } end: ASYNC_WAIT_CTX_free(ctx); printf("Finishing\n"); 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
SEE ALSO
crypto(3), ERR_print_errors(3)HISTORY
ASYNC_init_thread, ASYNC_cleanup_thread, ASYNC_start_job, ASYNC_pause_job, ASYNC_get_current_job, ASYNC_get_wait_ctx(), ASYNC_block_pause(), ASYNC_unblock_pause() and ASYNC_is_capable() were first added to OpenSSL 1.1.0.COPYRIGHT
Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.Licensed under the OpenSSL license (the ``License''). You may not use this file except in compliance with the License. You can obtain a copy in the file