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230 lines
11 KiB
Plaintext
230 lines
11 KiB
Plaintext
=pod
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=head1 NAME
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ASYNC_WAIT_CTX_new, ASYNC_WAIT_CTX_free, ASYNC_WAIT_CTX_set_wait_fd,
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ASYNC_WAIT_CTX_get_fd, ASYNC_WAIT_CTX_get_all_fds,
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ASYNC_WAIT_CTX_get_changed_fds, ASYNC_WAIT_CTX_clear_fd,
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ASYNC_WAIT_CTX_set_callback, ASYNC_WAIT_CTX_get_callback,
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ASYNC_WAIT_CTX_set_status, ASYNC_WAIT_CTX_get_status, ASYNC_callback_fn,
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ASYNC_STATUS_UNSUPPORTED, ASYNC_STATUS_ERR, ASYNC_STATUS_OK,
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ASYNC_STATUS_EAGAIN
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- functions to manage waiting for asynchronous jobs to complete
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=head1 SYNOPSIS
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#include <openssl/async.h>
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#define ASYNC_STATUS_UNSUPPORTED 0
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#define ASYNC_STATUS_ERR 1
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#define ASYNC_STATUS_OK 2
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#define ASYNC_STATUS_EAGAIN 3
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typedef int (*ASYNC_callback_fn)(void *arg);
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ASYNC_WAIT_CTX *ASYNC_WAIT_CTX_new(void);
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void ASYNC_WAIT_CTX_free(ASYNC_WAIT_CTX *ctx);
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int ASYNC_WAIT_CTX_set_wait_fd(ASYNC_WAIT_CTX *ctx, const void *key,
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OSSL_ASYNC_FD fd,
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void *custom_data,
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void (*cleanup)(ASYNC_WAIT_CTX *, const void *,
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OSSL_ASYNC_FD, void *));
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int ASYNC_WAIT_CTX_get_fd(ASYNC_WAIT_CTX *ctx, const void *key,
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OSSL_ASYNC_FD *fd, void **custom_data);
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int ASYNC_WAIT_CTX_get_all_fds(ASYNC_WAIT_CTX *ctx, OSSL_ASYNC_FD *fd,
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size_t *numfds);
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int ASYNC_WAIT_CTX_get_changed_fds(ASYNC_WAIT_CTX *ctx, OSSL_ASYNC_FD *addfd,
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size_t *numaddfds, OSSL_ASYNC_FD *delfd,
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size_t *numdelfds);
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int ASYNC_WAIT_CTX_clear_fd(ASYNC_WAIT_CTX *ctx, const void *key);
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int ASYNC_WAIT_CTX_set_callback(ASYNC_WAIT_CTX *ctx,
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ASYNC_callback_fn callback,
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void *callback_arg);
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int ASYNC_WAIT_CTX_get_callback(ASYNC_WAIT_CTX *ctx,
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ASYNC_callback_fn *callback,
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void **callback_arg);
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int ASYNC_WAIT_CTX_set_status(ASYNC_WAIT_CTX *ctx, int status);
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int ASYNC_WAIT_CTX_get_status(ASYNC_WAIT_CTX *ctx);
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=head1 DESCRIPTION
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For an overview of how asynchronous operations are implemented in OpenSSL see
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L<ASYNC_start_job(3)>. An B<ASYNC_WAIT_CTX> object represents an asynchronous
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"session", i.e. a related set of crypto operations. For example in SSL terms
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this would have a one-to-one correspondence with an SSL connection.
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Application code must create an B<ASYNC_WAIT_CTX> using the ASYNC_WAIT_CTX_new()
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function prior to calling ASYNC_start_job() (see L<ASYNC_start_job(3)>). When
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the job is started it is associated with the B<ASYNC_WAIT_CTX> for the duration
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of that job. An B<ASYNC_WAIT_CTX> should only be used for one B<ASYNC_JOB> at
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any one time, but can be reused after an B<ASYNC_JOB> has finished for a
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subsequent B<ASYNC_JOB>. When the session is complete (e.g. the SSL connection
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is closed), application code cleans up with ASYNC_WAIT_CTX_free().
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B<ASYNC_WAIT_CTX>s can have "wait" file descriptors associated with them.
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Calling ASYNC_WAIT_CTX_get_all_fds() and passing in a pointer to an
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B<ASYNC_WAIT_CTX> in the I<ctx> parameter will return the wait file descriptors
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associated with that job in I<*fd>. The number of file descriptors returned will
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be stored in I<*numfds>. It is the caller's responsibility to ensure that
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sufficient memory has been allocated in I<*fd> to receive all the file
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descriptors. Calling ASYNC_WAIT_CTX_get_all_fds() with a NULL I<fd> value will
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return no file descriptors but will still populate I<*numfds>. Therefore,
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application code is typically expected to call this function twice: once to get
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the number of fds, and then again when sufficient memory has been allocated. If
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only one asynchronous engine is being used then normally this call will only
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ever return one fd. If multiple asynchronous engines are being used then more
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could be returned.
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The function ASYNC_WAIT_CTX_get_changed_fds() can be used to detect if any fds
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have changed since the last call time ASYNC_start_job() returned B<ASYNC_PAUSE>
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(or since the B<ASYNC_WAIT_CTX> was created if no B<ASYNC_PAUSE> result has
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been received). The I<numaddfds> and I<numdelfds> parameters will be populated
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with the number of fds added or deleted respectively. I<*addfd> and I<*delfd>
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will be populated with the list of added and deleted fds respectively. Similarly
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to ASYNC_WAIT_CTX_get_all_fds() either of these can be NULL, but if they are not
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NULL then the caller is responsible for ensuring sufficient memory is allocated.
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Implementers of async aware code (e.g. engines) are encouraged to return a
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stable fd for the lifetime of the B<ASYNC_WAIT_CTX> in order to reduce the
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"churn" of regularly changing fds - although no guarantees of this are provided
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to applications.
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Applications can wait for the file descriptor to be ready for "read" using a
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system function call such as select or poll (being ready for "read" indicates
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that the job should be resumed). If no file descriptor is made available then an
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application will have to periodically "poll" the job by attempting to restart it
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to see if it is ready to continue.
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Async aware code (e.g. engines) can get the current B<ASYNC_WAIT_CTX> from the
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job via L<ASYNC_get_wait_ctx(3)> and provide a file descriptor to use for
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waiting on by calling ASYNC_WAIT_CTX_set_wait_fd(). Typically this would be done
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by an engine immediately prior to calling ASYNC_pause_job() and not by end user
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code. An existing association with a file descriptor can be obtained using
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ASYNC_WAIT_CTX_get_fd() and cleared using ASYNC_WAIT_CTX_clear_fd(). Both of
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these functions requires a I<key> value which is unique to the async aware
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code. This could be any unique value but a good candidate might be the
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B<ENGINE *> for the engine. The I<custom_data> parameter can be any value, and
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will be returned in a subsequent call to ASYNC_WAIT_CTX_get_fd(). The
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ASYNC_WAIT_CTX_set_wait_fd() function also expects a pointer to a "cleanup"
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routine. This can be NULL but if provided will automatically get called when
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the B<ASYNC_WAIT_CTX> is freed, and gives the engine the opportunity to close
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the fd or any other resources. Note: The "cleanup" routine does not get called
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if the fd is cleared directly via a call to ASYNC_WAIT_CTX_clear_fd().
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An example of typical usage might be an async capable engine. User code would
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initiate cryptographic operations. The engine would initiate those operations
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asynchronously and then call ASYNC_WAIT_CTX_set_wait_fd() followed by
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ASYNC_pause_job() to return control to the user code. The user code can then
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perform other tasks or wait for the job to be ready by calling "select" or other
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similar function on the wait file descriptor. The engine can signal to the user
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code that the job should be resumed by making the wait file descriptor
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"readable". Once resumed the engine should clear the wake signal on the wait
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file descriptor.
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As well as a file descriptor, user code may also be notified via a callback. The
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callback and data pointers are stored within the B<ASYNC_WAIT_CTX> along with an
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additional status field that can be used for the notification of retries from an
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engine. This additional method can be used when the user thinks that a file
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descriptor is too costly in terms of CPU cycles or in some context where a file
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descriptor is not appropriate.
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ASYNC_WAIT_CTX_set_callback() sets the callback and the callback argument. The
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callback will be called to notify user code when an engine completes a
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cryptography operation. It is a requirement that the callback function is small
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and nonblocking as it will be run in the context of a polling mechanism or an
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interrupt.
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ASYNC_WAIT_CTX_get_callback() returns the callback set in the B<ASYNC_WAIT_CTX>
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structure.
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ASYNC_WAIT_CTX_set_status() allows an engine to set the current engine status.
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The possible status values are the following:
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=over 4
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=item B<ASYNC_STATUS_UNSUPPORTED>
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The engine does not support the callback mechanism. This is the default value.
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The engine must call ASYNC_WAIT_CTX_set_status() to set the status to some value
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other than B<ASYNC_STATUS_UNSUPPORTED> if it intends to enable the callback
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mechanism.
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=item B<ASYNC_STATUS_ERR>
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The engine has a fatal problem with this request. The user code should clean up
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this session.
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=item B<ASYNC_STATUS_OK>
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The request has been successfully submitted.
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=item B<ASYNC_STATUS_EAGAIN>
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The engine has some problem which will be recovered soon, such as a buffer is
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full, so user code should resume the job.
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=back
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ASYNC_WAIT_CTX_get_status() allows user code to obtain the current status value.
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If the status is any value other than B<ASYNC_STATUS_OK> then the user code
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should not expect to receive a callback from the engine even if one has been
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set.
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An example of the usage of the callback method might be the following. User
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code would initiate cryptographic operations, and the engine code would dispatch
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this operation to hardware, and if the dispatch is successful, then the engine
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code would call ASYNC_pause_job() to return control to the user code. After
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that, user code can perform other tasks. When the hardware completes the
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operation, normally it is detected by a polling function or an interrupt, as the
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user code set a callback by calling ASYNC_WAIT_CTX_set_callback() previously,
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then the registered callback will be called.
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ASYNC_WAIT_CTX_free() frees up a single B<ASYNC_WAIT_CTX> object.
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If the argument is NULL, nothing is done.
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=head1 RETURN VALUES
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ASYNC_WAIT_CTX_new() returns a pointer to the newly allocated B<ASYNC_WAIT_CTX>
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or NULL on error.
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ASYNC_WAIT_CTX_set_wait_fd, ASYNC_WAIT_CTX_get_fd, ASYNC_WAIT_CTX_get_all_fds,
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ASYNC_WAIT_CTX_get_changed_fds, ASYNC_WAIT_CTX_clear_fd,
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ASYNC_WAIT_CTX_set_callback, ASYNC_WAIT_CTX_get_callback and
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ASYNC_WAIT_CTX_set_status all return 1 on success or 0 on error.
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ASYNC_WAIT_CTX_get_status() returns the engine status.
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=head1 NOTES
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On Windows platforms the F<< <openssl/async.h> >> header is dependent on some
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of the types customarily made available by including F<< <windows.h> >>. The
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application developer is likely to require control over when the latter
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is included, commonly as one of the first included headers. Therefore,
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it is defined as an application developer's responsibility to include
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F<< <windows.h> >> prior to F<< <openssl/async.h> >>.
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=head1 SEE ALSO
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L<crypto(7)>, L<ASYNC_start_job(3)>
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=head1 HISTORY
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ASYNC_WAIT_CTX_new(), ASYNC_WAIT_CTX_free(), ASYNC_WAIT_CTX_set_wait_fd(),
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ASYNC_WAIT_CTX_get_fd(), ASYNC_WAIT_CTX_get_all_fds(),
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ASYNC_WAIT_CTX_get_changed_fds() and ASYNC_WAIT_CTX_clear_fd()
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were added in OpenSSL 1.1.0.
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ASYNC_WAIT_CTX_set_callback(), ASYNC_WAIT_CTX_get_callback(),
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ASYNC_WAIT_CTX_set_status(), and ASYNC_WAIT_CTX_get_status()
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were added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2016-2024 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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