1=pod
2
3=head1 NAME
4
5ASYNC_WAIT_CTX_new, ASYNC_WAIT_CTX_free, ASYNC_WAIT_CTX_set_wait_fd,
6ASYNC_WAIT_CTX_get_fd, ASYNC_WAIT_CTX_get_all_fds,
7ASYNC_WAIT_CTX_get_changed_fds, ASYNC_WAIT_CTX_clear_fd - functions to manage
8waiting for asynchronous jobs to complete
9
10=head1 SYNOPSIS
11
12 #include <openssl/async.h>
13
14 ASYNC_WAIT_CTX *ASYNC_WAIT_CTX_new(void);
15 void ASYNC_WAIT_CTX_free(ASYNC_WAIT_CTX *ctx);
16 int ASYNC_WAIT_CTX_set_wait_fd(ASYNC_WAIT_CTX *ctx, const void *key,
17                                OSSL_ASYNC_FD fd,
18                                void *custom_data,
19                                void (*cleanup)(ASYNC_WAIT_CTX *, const void *,
20                                                OSSL_ASYNC_FD, void *));
21 int ASYNC_WAIT_CTX_get_fd(ASYNC_WAIT_CTX *ctx, const void *key,
22                           OSSL_ASYNC_FD *fd, void **custom_data);
23 int ASYNC_WAIT_CTX_get_all_fds(ASYNC_WAIT_CTX *ctx, OSSL_ASYNC_FD *fd,
24                                size_t *numfds);
25 int ASYNC_WAIT_CTX_get_changed_fds(ASYNC_WAIT_CTX *ctx, OSSL_ASYNC_FD *addfd,
26                                    size_t *numaddfds, OSSL_ASYNC_FD *delfd,
27                                    size_t *numdelfds);
28 int ASYNC_WAIT_CTX_clear_fd(ASYNC_WAIT_CTX *ctx, const void *key);
29
30
31=head1 DESCRIPTION
32
33For an overview of how asynchronous operations are implemented in OpenSSL see
34L<ASYNC_start_job(3)>. An ASYNC_WAIT_CTX object represents an asynchronous
35"session", i.e. a related set of crypto operations. For example in SSL terms
36this would have a one-to-one correspondence with an SSL connection.
37
38Application code must create an ASYNC_WAIT_CTX using the ASYNC_WAIT_CTX_new()
39function prior to calling ASYNC_start_job() (see L<ASYNC_start_job(3)>). When
40the job is started it is associated with the ASYNC_WAIT_CTX for the duration of
41that job. An ASYNC_WAIT_CTX should only be used for one ASYNC_JOB at any one
42time, but can be reused after an ASYNC_JOB has finished for a subsequent
43ASYNC_JOB. When the session is complete (e.g. the SSL connection is closed),
44application code cleans up with ASYNC_WAIT_CTX_free().
45
46ASYNC_WAIT_CTXs can have "wait" file descriptors associated with them. Calling
47ASYNC_WAIT_CTX_get_all_fds() and passing in a pointer to an ASYNC_WAIT_CTX in
48the B<ctx> parameter will return the wait file descriptors associated with that
49job in B<*fd>. The number of file descriptors returned will be stored in
50B<*numfds>. It is the caller's responsibility to ensure that sufficient memory
51has been allocated in B<*fd> to receive all the file descriptors. Calling
52ASYNC_WAIT_CTX_get_all_fds() with a NULL B<fd> value will return no file
53descriptors but will still populate B<*numfds>. Therefore application code is
54typically expected to call this function twice: once to get the number of fds,
55and then again when sufficient memory has been allocated. If only one
56asynchronous engine is being used then normally this call will only ever return
57one fd. If multiple asynchronous engines are being used then more could be
58returned.
59
60The function ASYNC_WAIT_CTX_get_changed_fds() can be used to detect if any fds
61have changed since the last call time ASYNC_start_job() returned an ASYNC_PAUSE
62result (or since the ASYNC_WAIT_CTX was created if no ASYNC_PAUSE result has
63been received). The B<numaddfds> and B<numdelfds> parameters will be populated
64with the number of fds added or deleted respectively. B<*addfd> and B<*delfd>
65will be populated with the list of added and deleted fds respectively. Similarly
66to ASYNC_WAIT_CTX_get_all_fds() either of these can be NULL, but if they are not
67NULL then the caller is responsible for ensuring sufficient memory is allocated.
68
69Implementors of async aware code (e.g. engines) are encouraged to return a
70stable fd for the lifetime of the ASYNC_WAIT_CTX in order to reduce the "churn"
71of regularly changing fds - although no guarantees of this are provided to
72applications.
73
74Applications can wait for the file descriptor to be ready for "read" using a
75system function call such as select or poll (being ready for "read" indicates
76that the job should be resumed). If no file descriptor is made available then an
77application will have to periodically "poll" the job by attempting to restart it
78to see if it is ready to continue.
79
80Async aware code (e.g. engines) can get the current ASYNC_WAIT_CTX from the job
81via L<ASYNC_get_wait_ctx(3)> and provide a file descriptor to use for waiting
82on by calling ASYNC_WAIT_CTX_set_wait_fd(). Typically this would be done by an
83engine immediately prior to calling ASYNC_pause_job() and not by end user code.
84An existing association with a file descriptor can be obtained using
85ASYNC_WAIT_CTX_get_fd() and cleared using ASYNC_WAIT_CTX_clear_fd(). Both of
86these functions requires a B<key> value which is unique to the async aware
87code.  This could be any unique value but a good candidate might be the
88B<ENGINE *> for the engine. The B<custom_data> parameter can be any value, and
89will be returned in a subsequent call to ASYNC_WAIT_CTX_get_fd(). The
90ASYNC_WAIT_CTX_set_wait_fd() function also expects a pointer to a "cleanup"
91routine. This can be NULL but if provided will automatically get called when
92the ASYNC_WAIT_CTX is freed, and gives the engine the opportunity to close the
93fd or any other resources. Note: The "cleanup" routine does not get called if
94the fd is cleared directly via a call to ASYNC_WAIT_CTX_clear_fd().
95
96An example of typical usage might be an async capable engine. User code would
97initiate cryptographic operations. The engine would initiate those operations
98asynchronously and then call ASYNC_WAIT_CTX_set_wait_fd() followed by
99ASYNC_pause_job() to return control to the user code. The user code can then
100perform other tasks or wait for the job to be ready by calling "select" or other
101similar function on the wait file descriptor. The engine can signal to the user
102code that the job should be resumed by making the wait file descriptor
103"readable". Once resumed the engine should clear the wake signal on the wait
104file descriptor.
105
106=head1 RETURN VALUES
107
108ASYNC_WAIT_CTX_new() returns a pointer to the newly allocated ASYNC_WAIT_CTX or
109NULL on error.
110
111ASYNC_WAIT_CTX_set_wait_fd, ASYNC_WAIT_CTX_get_fd, ASYNC_WAIT_CTX_get_all_fds,
112ASYNC_WAIT_CTX_get_changed_fds and ASYNC_WAIT_CTX_clear_fd all return 1 on
113success or 0 on error.
114
115=head1 NOTES
116
117On Windows platforms the openssl/async.h header is dependent on some
118of the types customarily made available by including windows.h. The
119application developer is likely to require control over when the latter
120is included, commonly as one of the first included headers. Therefore
121it is defined as an application developer's responsibility to include
122windows.h prior to async.h.
123
124=head1 SEE ALSO
125
126L<crypto(7)>, L<ASYNC_start_job(3)>
127
128=head1 HISTORY
129
130ASYNC_WAIT_CTX_new(), ASYNC_WAIT_CTX_free(), ASYNC_WAIT_CTX_set_wait_fd(),
131ASYNC_WAIT_CTX_get_fd(), ASYNC_WAIT_CTX_get_all_fds(),
132ASYNC_WAIT_CTX_get_changed_fds() and ASYNC_WAIT_CTX_clear_fd()
133were added in OpenSSL 1.1.0.
134
135=head1 COPYRIGHT
136
137Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
138
139Licensed under the OpenSSL license (the "License").  You may not use
140this file except in compliance with the License.  You can obtain a copy
141in the file LICENSE in the source distribution or at
142L<https://www.openssl.org/source/license.html>.
143
144=cut
145