1ASYNC_START_JOB(3ossl) OpenSSL ASYNC_START_JOB(3ossl)
2
6 ASYNC_get_wait_ctx, ASYNC_init_thread, ASYNC_cleanup_thread,
7 ASYNC_start_job, ASYNC_pause_job, ASYNC_get_current_job,
8 ASYNC_block_pause, ASYNC_unblock_pause, ASYNC_is_capable - asynchronous
9 job management functions
10
12 #include <openssl/async.h>
13 int ASYNC_init_thread(size_t max_size, size_t init_size);
15 void ASYNC_cleanup_thread(void);
16 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);
20 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);
25 int ASYNC_is_capable(void);
27
29 OpenSSL implements asynchronous capabilities through an ASYNC_JOB. This
30 represents code that can be started and executes until some event
31 occurs. At that point the code can be paused and control returns to
32 user code until some subsequent event indicates that the job can be
33 resumed.
34 The creation of an ASYNC_JOB is a relatively expensive operation.
36 Therefore, for efficiency reasons, jobs can be created up front and
37 reused many times. They are held in a pool until they are needed, at
38 which point they are removed from the pool, used, and then returned to
39 the pool when the job completes. If the user application is multi-
40 threaded, then ASYNC_init_thread() may be called for each thread that
41 will initiate asynchronous jobs. Before user code exits per-thread
42 resources need to be cleaned up. This will normally occur automatically
43 (see OPENSSL_init_crypto(3)) but may be explicitly initiated by using
44 ASYNC_cleanup_thread(). No asynchronous jobs must be outstanding for
45 the thread when ASYNC_cleanup_thread() is called. Failing to ensure
46 this will result in memory leaks.
47 The max_size argument limits the number of ASYNC_JOBs that will be held
49 in the pool. If max_size is set to 0 then no upper limit is set. When
50 an ASYNC_JOB is needed but there are none available in the pool already
51 then one will be automatically created, as long as the total of
52 ASYNC_JOBs managed by the pool does not exceed max_size. When the pool
53 is first initialised init_size ASYNC_JOBs will be created immediately.
54 If ASYNC_init_thread() is not called before the pool is first used then
55 it will be called automatically with a max_size of 0 (no upper limit)
56 and an init_size of 0 (no ASYNC_JOBs created up front).
57 An asynchronous job is started by calling the ASYNC_start_job()
59 function. Initially *job should be NULL. ctx should point to an
60 ASYNC_WAIT_CTX object created through the ASYNC_WAIT_CTX_new(3)
61 function. ret should point to a location where the return value of the
62 asynchronous function should be stored on completion of the job. func
63 represents the function that should be started asynchronously. The data
64 pointed to by args and of size size will be copied and then passed as
65 an argument to func when the job starts. ASYNC_start_job will return
66 one of the following values:
67 ASYNC_ERR
69 An error occurred trying to start the job. Check the OpenSSL error
70 queue (e.g. see ERR_print_errors(3)) for more details.
71 ASYNC_NO_JOBS
73 There are no jobs currently available in the pool. This call can be
74 retried again at a later time.
75 ASYNC_PAUSE
77 The job was successfully started but was "paused" before it
78 completed (see ASYNC_pause_job() below). A handle to the job is
79 placed in *job. Other work can be performed (if desired) and the
80 job restarted at a later time. To restart a job call
81 ASYNC_start_job() again passing the job handle in *job. The func,
82 args and size parameters will be ignored when restarting a job.
83 When restarting a job ASYNC_start_job() must be called from the
84 same thread that the job was originally started from.
85 ASYNC_FINISH
87 The job completed. *job will be NULL and the return value from func
88 will be placed in *ret.
89 At any one time there can be a maximum of one job actively running per
91 thread (you can have many that are paused). ASYNC_get_current_job() can
92 be used to get a pointer to the currently executing ASYNC_JOB. If no
93 job is currently executing then this will return NULL.
94 If executing within the context of a job (i.e. having been called
96 directly or indirectly by the function "func" passed as an argument to
97 ASYNC_start_job()) then ASYNC_pause_job() will immediately return
98 control to the calling application with ASYNC_PAUSE returned from the
99 ASYNC_start_job() call. A subsequent call to ASYNC_start_job passing in
100 the relevant ASYNC_JOB in the *job parameter will resume execution from
101 the ASYNC_pause_job() call. If ASYNC_pause_job() is called whilst not
102 within the context of a job then no action is taken and
103 ASYNC_pause_job() returns immediately.
104 ASYNC_get_wait_ctx() can be used to get a pointer to the ASYNC_WAIT_CTX
106 for the job. ASYNC_WAIT_CTXs contain two different ways to notify
107 applications that a job is ready to be resumed. One is a "wait" file
108 descriptor, and the other is a "callback" mechanism.
109 The "wait" file descriptor associated with ASYNC_WAIT_CTX is used for
111 applications to wait for the file descriptor to be ready for "read"
112 using a system function call such as select or poll (being ready for
113 "read" indicates that the job should be resumed). If no file descriptor
114 is made available then an application will have to periodically "poll"
115 the job by attempting to restart it to see if it is ready to continue.
116 ASYNC_WAIT_CTXs also have a "callback" mechanism to notify
118 applications. The callback is set by an application, and it will be
119 automatically called when an engine completes a cryptography operation,
120 so that the application can resume the paused work flow without
121 polling. An engine could be written to look whether the callback has
122 been set. If it has then it would use the callback mechanism in
123 preference to the file descriptor notifications. If a callback is not
124 set then the engine may use file descriptor based notifications. Please
125 note that not all engines may support the callback mechanism, so the
126 callback may not be used even if it has been set. See
127 ASYNC_WAIT_CTX_new() for more details.
128 The ASYNC_block_pause() function will prevent the currently active job
130 from pausing. The block will remain in place until a subsequent call to
131 ASYNC_unblock_pause(). These functions can be nested, e.g. if you call
132 ASYNC_block_pause() twice then you must call ASYNC_unblock_pause()
133 twice in order to re-enable pausing. If these functions are called
134 while there is no currently active job then they have no effect. This
135 functionality can be useful to avoid deadlock scenarios. For example
136 during the execution of an ASYNC_JOB an application acquires a lock. It
137 then calls some cryptographic function which invokes ASYNC_pause_job().
138 This returns control back to the code that created the ASYNC_JOB. If
139 that code then attempts to acquire the same lock before resuming the
140 original job then a deadlock can occur. By calling ASYNC_block_pause()
141 immediately after acquiring the lock and ASYNC_unblock_pause()
142 immediately before releasing it then this situation cannot occur.
143 Some platforms cannot support async operations. The ASYNC_is_capable()
145 function can be used to detect whether the current platform is async
146 capable or not.
147
149 ASYNC_init_thread returns 1 on success or 0 otherwise.
150 ASYNC_start_job returns one of ASYNC_ERR, ASYNC_NO_JOBS, ASYNC_PAUSE or
152 ASYNC_FINISH as described above.
153 ASYNC_pause_job returns 0 if an error occurred or 1 on success. If
155 called when not within the context of an ASYNC_JOB then this is counted
156 as success so 1 is returned.
157 ASYNC_get_current_job returns a pointer to the currently executing
159 ASYNC_JOB or NULL if not within the context of a job.
160 ASYNC_get_wait_ctx() returns a pointer to the ASYNC_WAIT_CTX for the
162 job.
163 ASYNC_is_capable() returns 1 if the current platform is async capable
165 or 0 otherwise.
166
168 On Windows platforms the <openssl/async.h> header is dependent on some
169 of the types customarily made available by including <windows.h>. The
170 application developer is likely to require control over when the latter
171 is included, commonly as one of the first included headers. Therefore,
172 it is defined as an application developer's responsibility to include
173 <windows.h> prior to <openssl/async.h>.
174
176 The following example demonstrates how to use most of the core async
177 APIs:
178 #ifdef _WIN32
180 # include <windows.h>
181 #endif
182 #include <stdio.h>
183 #include <unistd.h>
184 #include <openssl/async.h>
185 #include <openssl/crypto.h>
186 int unique = 0;
188 void cleanup(ASYNC_WAIT_CTX *ctx, const void *key, OSSL_ASYNC_FD r, void *vw)
190 {
191 OSSL_ASYNC_FD *w = (OSSL_ASYNC_FD *)vw;
192 close(r);
194 close(*w);
195 OPENSSL_free(w);
196 }
197 int jobfunc(void *arg)
199 {
200 ASYNC_JOB *currjob;
201 unsigned char *msg;
202 int pipefds[2] = {0, 0};
203 OSSL_ASYNC_FD *wptr;
204 char buf = 'X';
205 currjob = ASYNC_get_current_job();
207 if (currjob != NULL) {
208 printf("Executing within a job\n");
209 } else {
210 printf("Not executing within a job - should not happen\n");
211 return 0;
212 }
213 msg = (unsigned char *)arg;
215 printf("Passed in message is: %s\n", msg);
216 if (pipe(pipefds) != 0) {
218 printf("Failed to create pipe\n");
219 return 0;
220 }
221 wptr = OPENSSL_malloc(sizeof(OSSL_ASYNC_FD));
222 if (wptr == NULL) {
223 printf("Failed to malloc\n");
224 return 0;
225 }
226 *wptr = pipefds[1];
227 ASYNC_WAIT_CTX_set_wait_fd(ASYNC_get_wait_ctx(currjob), &unique,
228 pipefds[0], wptr, cleanup);
229 /*
231 * Normally some external event would cause this to happen at some
232 * later point - but we do it here for demo purposes, i.e.
233 * immediately signalling that the job is ready to be woken up after
234 * we return to main via ASYNC_pause_job().
235 */
236 write(pipefds[1], &buf, 1);
237 /* Return control back to main */
239 ASYNC_pause_job();
240 /* Clear the wake signal */
242 read(pipefds[0], &buf, 1);
243 printf ("Resumed the job after a pause\n");
245 return 1;
247 }
248 int main(void)
250 {
251 ASYNC_JOB *job = NULL;
252 ASYNC_WAIT_CTX *ctx = NULL;
253 int ret;
254 OSSL_ASYNC_FD waitfd;
255 fd_set waitfdset;
256 size_t numfds;
257 unsigned char msg[13] = "Hello world!";
258 printf("Starting...\n");
260 ctx = ASYNC_WAIT_CTX_new();
262 if (ctx == NULL) {
263 printf("Failed to create ASYNC_WAIT_CTX\n");
264 abort();
265 }
266 for (;;) {
268 switch (ASYNC_start_job(&job, ctx, &ret, jobfunc, msg, sizeof(msg))) {
269 case ASYNC_ERR:
270 case ASYNC_NO_JOBS:
271 printf("An error occurred\n");
272 goto end;
273 case ASYNC_PAUSE:
274 printf("Job was paused\n");
275 break;
276 case ASYNC_FINISH:
277 printf("Job finished with return value %d\n", ret);
278 goto end;
279 }
280 /* Wait for the job to be woken */
282 printf("Waiting for the job to be woken up\n");
283 if (!ASYNC_WAIT_CTX_get_all_fds(ctx, NULL, &numfds)
285 || numfds > 1) {
286 printf("Unexpected number of fds\n");
287 abort();
288 }
289 ASYNC_WAIT_CTX_get_all_fds(ctx, &waitfd, &numfds);
290 FD_ZERO(&waitfdset);
291 FD_SET(waitfd, &waitfdset);
292 select(waitfd + 1, &waitfdset, NULL, NULL, NULL);
293 }
294 end:
296 ASYNC_WAIT_CTX_free(ctx);
297 printf("Finishing\n");
298 return 0;
300 }
301 The expected output from executing the above example program is:
303 Starting...
305 Executing within a job
306 Passed in message is: Hello world!
307 Job was paused
308 Waiting for the job to be woken up
309 Resumed the job after a pause
310 Job finished with return value 1
311 Finishing
312
314 crypto(7), ERR_print_errors(3)
315
317 ASYNC_init_thread, ASYNC_cleanup_thread, ASYNC_start_job,
318 ASYNC_pause_job, ASYNC_get_current_job, ASYNC_get_wait_ctx(),
319 ASYNC_block_pause(), ASYNC_unblock_pause() and ASYNC_is_capable() were
320 first added in OpenSSL 1.1.0.
321
323 Copyright 2015-2021 The OpenSSL Project Authors. All Rights Reserved.
324 Licensed under the Apache License 2.0 (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 <https://www.openssl.org/source/license.html>.
3293.0.9 2023-07-27 ASYNC_START_JOB(3ossl)