6 ASYNC_init_thread, ASYNC_cleanup_thread, ASYNC_start_job, ASYNC_pause_job,
7 ASYNC_get_current_job, ASYNC_block_pause, ASYNC_unblock_pause, ASYNC_is_capable
8 - asynchronous job management functions
12 #include <openssl/async.h>
14 int ASYNC_init_thread(size_t max_size, size_t init_size);
15 void ASYNC_cleanup_thread(void);
17 int ASYNC_start_job(ASYNC_JOB **job, ASYNC_WAIT_CTX *ctx, int *ret,
18 int (*func)(void *), void *args, size_t size);
19 int ASYNC_pause_job(void);
21 ASYNC_JOB *ASYNC_get_current_job(void);
22 ASYNC_WAIT_CTX *ASYNC_get_wait_ctx(ASYNC_JOB *job);
23 void ASYNC_block_pause(void);
24 void ASYNC_unblock_pause(void);
26 int ASYNC_is_capable(void);
30 OpenSSL implements asynchronous capabilities through an ASYNC_JOB. This
31 represents code that can be started and executes until some event occurs. At
32 that point the code can be paused and control returns to user code until some
33 subsequent event indicates that the job can be resumed.
35 The creation of an ASYNC_JOB is a relatively expensive operation. Therefore, for
36 efficiency reasons, jobs can be created up front and reused many times. They are
37 held in a pool until they are needed, at which point they are removed from the
38 pool, used, and then returned to the pool when the job completes. If the user
39 application is multi-threaded, then ASYNC_init_thread() may be called for each
40 thread that will initiate asynchronous jobs. Before
41 user code exits per-thread resources need to be cleaned up. This will normally
42 occur automatically (see L<OPENSSL_init_crypto(3)>) but may be explicitly
43 initiated by using ASYNC_cleanup_thread(). No asynchronous jobs must be
44 outstanding for the thread when ASYNC_cleanup_thread() is called. Failing to
45 ensure this will result in memory leaks.
47 The B<max_size> argument limits the number of ASYNC_JOBs that will be held in
48 the pool. If B<max_size> is set to 0 then no upper limit is set. When an
49 ASYNC_JOB is needed but there are none available in the pool already then one
50 will be automatically created, as long as the total of ASYNC_JOBs managed by the
51 pool does not exceed B<max_size>. When the pool is first initialised
52 B<init_size> ASYNC_JOBs will be created immediately. If ASYNC_init_thread() is
53 not called before the pool is first used then it will be called automatically
54 with a B<max_size> of 0 (no upper limit) and an B<init_size> of 0 (no ASYNC_JOBs
57 An asynchronous job is started by calling the ASYNC_start_job() function.
58 Initially B<*job> should be NULL. B<ctx> should point to an ASYNC_WAIT_CTX
59 object created through the L<ASYNC_WAIT_CTX_new(3)> function. B<ret> should
60 point to a location where the return value of the asynchronous function should
61 be stored on completion of the job. B<func> represents the function that should
62 be started asynchronously. The data pointed to by B<args> and of size B<size>
63 will be copied and then passed as an argument to B<func> when the job starts.
64 ASYNC_start_job will return one of the following values:
70 An error occurred trying to start the job. Check the OpenSSL error queue (e.g.
71 see L<ERR_print_errors(3)>) for more details.
73 =item B<ASYNC_NO_JOBS>
75 There are no jobs currently available in the pool. This call can be retried
76 again at a later time.
80 The job was successfully started but was "paused" before it completed (see
81 ASYNC_pause_job() below). A handle to the job is placed in B<*job>. Other work
82 can be performed (if desired) and the job restarted at a later time. To restart
83 a job call ASYNC_start_job() again passing the job handle in B<*job>. The
84 B<func>, B<args> and B<size> parameters will be ignored when restarting a job.
85 When restarting a job ASYNC_start_job() B<must> be called from the same thread
86 that the job was originally started from.
90 The job completed. B<*job> will be NULL and the return value from B<func> will
95 At any one time there can be a maximum of one job actively running per thread
96 (you can have many that are paused). ASYNC_get_current_job() can be used to get
97 a pointer to the currently executing ASYNC_JOB. If no job is currently executing
98 then this will return NULL.
100 If executing within the context of a job (i.e. having been called directly or
101 indirectly by the function "func" passed as an argument to ASYNC_start_job())
102 then ASYNC_pause_job() will immediately return control to the calling
103 application with ASYNC_PAUSE returned from the ASYNC_start_job() call. A
104 subsequent call to ASYNC_start_job passing in the relevant ASYNC_JOB in the
105 B<*job> parameter will resume execution from the ASYNC_pause_job() call. If
106 ASYNC_pause_job() is called whilst not within the context of a job then no
107 action is taken and ASYNC_pause_job() returns immediately.
109 ASYNC_get_wait_ctx() can be used to get a pointer to the ASYNC_WAIT_CTX
110 for the B<job>. ASYNC_WAIT_CTXs can have a "wait" file descriptor associated
111 with them. Applications can wait for the file descriptor to be ready for "read"
112 using a system function call such as select or poll (being ready for "read"
113 indicates that the job should be resumed). If no file descriptor is made
114 available then an application will have to periodically "poll" the job by
115 attempting to restart it to see if it is ready to continue.
117 An example of typical usage might be an async capable engine. User code would
118 initiate cryptographic operations. The engine would initiate those operations
119 asynchronously and then call L<ASYNC_WAIT_CTX_set_wait_fd(3)> followed by
120 ASYNC_pause_job() to return control to the user code. The user code can then
121 perform other tasks or wait for the job to be ready by calling "select" or other
122 similar function on the wait file descriptor. The engine can signal to the user
123 code that the job should be resumed by making the wait file descriptor
124 "readable". Once resumed the engine should clear the wake signal on the wait
127 The ASYNC_block_pause() function will prevent the currently active job from
128 pausing. The block will remain in place until a subsequent call to
129 ASYNC_unblock_pause(). These functions can be nested, e.g. if you call
130 ASYNC_block_pause() twice then you must call ASYNC_unblock_pause() twice in
131 order to re-enable pausing. If these functions are called while there is no
132 currently active job then they have no effect. This functionality can be useful
133 to avoid deadlock scenarios. For example during the execution of an ASYNC_JOB an
134 application acquires a lock. It then calls some cryptographic function which
135 invokes ASYNC_pause_job(). This returns control back to the code that created
136 the ASYNC_JOB. If that code then attempts to acquire the same lock before
137 resuming the original job then a deadlock can occur. By calling
138 ASYNC_block_pause() immediately after acquiring the lock and
139 ASYNC_unblock_pause() immediately before releasing it then this situation cannot
142 Some platforms cannot support async operations. The ASYNC_is_capable() function
143 can be used to detect whether the current platform is async capable or not.
147 ASYNC_init_thread returns 1 on success or 0 otherwise.
149 ASYNC_start_job returns one of ASYNC_ERR, ASYNC_NO_JOBS, ASYNC_PAUSE or
150 ASYNC_FINISH as described above.
152 ASYNC_pause_job returns 0 if an error occurred or 1 on success. If called when
153 not within the context of an ASYNC_JOB then this is counted as success so 1 is
156 ASYNC_get_current_job returns a pointer to the currently executing ASYNC_JOB or
157 NULL if not within the context of a job.
159 ASYNC_get_wait_ctx() returns a pointer to the ASYNC_WAIT_CTX for the job.
161 ASYNC_is_capable() returns 1 if the current platform is async capable or 0
166 On Windows platforms the openssl/async.h header is dependent on some
167 of the types customarily made available by including windows.h. The
168 application developer is likely to require control over when the latter
169 is included, commonly as one of the first included headers. Therefore
170 it is defined as an application developer's responsibility to include
171 windows.h prior to async.h.
175 The following example demonstrates how to use most of the core async APIs:
178 # include <windows.h>
182 #include <openssl/async.h>
183 #include <openssl/crypto.h>
187 void cleanup(ASYNC_WAIT_CTX *ctx, const void *key, OSSL_ASYNC_FD r, void *vw)
189 OSSL_ASYNC_FD *w = (OSSL_ASYNC_FD *)vw;
195 int jobfunc(void *arg)
199 int pipefds[2] = {0, 0};
203 currjob = ASYNC_get_current_job();
204 if (currjob != NULL) {
205 printf("Executing within a job\n");
207 printf("Not executing within a job - should not happen\n");
211 msg = (unsigned char *)arg;
212 printf("Passed in message is: %s\n", msg);
214 if (pipe(pipefds) != 0) {
215 printf("Failed to create pipe\n");
218 wptr = OPENSSL_malloc(sizeof(OSSL_ASYNC_FD));
220 printf("Failed to malloc\n");
224 ASYNC_WAIT_CTX_set_wait_fd(ASYNC_get_wait_ctx(currjob), &unique,
225 pipefds[0], wptr, cleanup);
228 * Normally some external event would cause this to happen at some
229 * later point - but we do it here for demo purposes, i.e.
230 * immediately signalling that the job is ready to be woken up after
231 * we return to main via ASYNC_pause_job().
233 write(pipefds[1], &buf, 1);
235 /* Return control back to main */
238 /* Clear the wake signal */
239 read(pipefds[0], &buf, 1);
241 printf ("Resumed the job after a pause\n");
248 ASYNC_JOB *job = NULL;
249 ASYNC_WAIT_CTX *ctx = NULL;
251 OSSL_ASYNC_FD waitfd;
254 unsigned char msg[13] = "Hello world!";
256 printf("Starting...\n");
258 ctx = ASYNC_WAIT_CTX_new();
260 printf("Failed to create ASYNC_WAIT_CTX\n");
265 switch(ASYNC_start_job(&job, ctx, &ret, jobfunc, msg, sizeof(msg))) {
268 printf("An error occurred\n");
271 printf("Job was paused\n");
274 printf("Job finished with return value %d\n", ret);
278 /* Wait for the job to be woken */
279 printf("Waiting for the job to be woken up\n");
281 if (!ASYNC_WAIT_CTX_get_all_fds(ctx, NULL, &numfds)
283 printf("Unexpected number of fds\n");
286 ASYNC_WAIT_CTX_get_all_fds(ctx, &waitfd, &numfds);
288 FD_SET(waitfd, &waitfdset);
289 select(waitfd + 1, &waitfdset, NULL, NULL, NULL);
293 ASYNC_WAIT_CTX_free(ctx);
294 printf("Finishing\n");
299 The expected output from executing the above example program is:
302 Executing within a job
303 Passed in message is: Hello world!
305 Waiting for the job to be woken up
306 Resumed the job after a pause
307 Job finished with return value 1
312 L<crypto(3)>, L<ERR_print_errors(3)>
316 ASYNC_init_thread, ASYNC_cleanup_thread,
317 ASYNC_start_job, ASYNC_pause_job, ASYNC_get_current_job, ASYNC_get_wait_ctx(),
318 ASYNC_block_pause(), ASYNC_unblock_pause() and ASYNC_is_capable() were first
319 added to OpenSSL 1.1.0.
323 Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.
325 Licensed under the OpenSSL license (the "License"). You may not use
326 this file except in compliance with the License. You can obtain a copy
327 in the file LICENSE in the source distribution or at
328 L<https://www.openssl.org/source/license.html>.