327 lines
10 KiB
C
327 lines
10 KiB
C
/*
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* QEMU I/O task
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*
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* Copyright (c) 2015 Red Hat, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#ifndef QIO_TASK_H
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#define QIO_TASK_H
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#include "qemu-common.h"
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#include "qom/object.h"
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typedef struct QIOTask QIOTask;
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typedef void (*QIOTaskFunc)(QIOTask *task,
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gpointer opaque);
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typedef void (*QIOTaskWorker)(QIOTask *task,
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gpointer opaque);
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/**
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* QIOTask:
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*
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* The QIOTask object provides a simple mechanism for reporting
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* success / failure of long running background operations.
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*
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* A object on which the operation is to be performed could have
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* a public API which accepts a task callback:
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*
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* <example>
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* <title>Task function signature</title>
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* <programlisting>
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* void myobject_operation(QMyObject *obj,
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* QIOTaskFunc *func,
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* gpointer opaque,
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* GDestroyNotify notify);
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* </programlisting>
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* </example>
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*
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* The 'func' parameter is the callback to be invoked, and 'opaque'
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* is data to pass to it. The optional 'notify' function is used
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* to free 'opaque' when no longer needed.
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*
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* When the operation completes, the 'func' callback will be
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* invoked, allowing the calling code to determine the result
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* of the operation. An example QIOTaskFunc implementation may
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* look like
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*
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* <example>
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* <title>Task callback implementation</title>
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* <programlisting>
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* static void myobject_operation_notify(QIOTask *task,
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* gpointer opaque)
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* {
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* Error *err = NULL;
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* if (qio_task_propagate_error(task, &err)) {
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* ...deal with the failure...
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* error_free(err);
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* } else {
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* QMyObject *src = QMY_OBJECT(qio_task_get_source(task));
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* ...deal with the completion...
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* }
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* }
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* </programlisting>
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* </example>
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*
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* Now, lets say the implementation of the method using the
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* task wants to set a timer to run once a second checking
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* for completion of some activity. It would do something
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* like
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*
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* <example>
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* <title>Task function implementation</title>
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* <programlisting>
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* void myobject_operation(QMyObject *obj,
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* QIOTaskFunc *func,
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* gpointer opaque,
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* GDestroyNotify notify)
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* {
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* QIOTask *task;
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*
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* task = qio_task_new(OBJECT(obj), func, opaque, notify);
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*
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* g_timeout_add_full(G_PRIORITY_DEFAULT,
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* 1000,
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* myobject_operation_timer,
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* task,
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* NULL);
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* }
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* </programlisting>
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* </example>
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*
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* It could equally have setup a watch on a file descriptor or
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* created a background thread, or something else entirely.
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* Notice that the source object is passed to the task, and
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* QIOTask will hold a reference on that. This ensure that
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* the QMyObject instance cannot be garbage collected while
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* the async task is still in progress.
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*
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* In this case, myobject_operation_timer will fire after
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* 3 secs and do
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*
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* <example>
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* <title>Task timer function</title>
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* <programlisting>
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* gboolean myobject_operation_timer(gpointer opaque)
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* {
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* QIOTask *task = QIO_TASK(opaque);
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* Error *err;*
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*
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* ...check something important...
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* if (err) {
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* qio_task_set_error(task, err);
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* qio_task_complete(task);
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* return FALSE;
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* } else if (...work is completed ...) {
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* qio_task_complete(task);
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* return FALSE;
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* }
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* ...carry on polling ...
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* return TRUE;
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* }
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* </programlisting>
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* </example>
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*
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* The 'qio_task_complete' call in this method will trigger
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* the callback func 'myobject_operation_notify' shown
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* earlier to deal with the results.
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*
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* Once this function returns false, object_unref will be called
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* automatically on the task causing it to be released and the
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* ref on QMyObject dropped too.
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*
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* The QIOTask module can also be used to perform operations
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* in a background thread context, while still reporting the
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* results in the main event thread. This allows code which
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* cannot easily be rewritten to be asychronous (such as DNS
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* lookups) to be easily run non-blocking. Reporting the
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* results in the main thread context means that the caller
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* typically does not need to be concerned about thread
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* safety wrt the QEMU global mutex.
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*
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* For example, the socket_listen() method will block the caller
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* while DNS lookups take place if given a name, instead of IP
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* address. The C library often do not provide a practical async
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* DNS API, so the to get non-blocking DNS lookups in a portable
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* manner requires use of a thread. So achieve a non-blocking
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* socket listen using QIOTask would require:
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*
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* <example>
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* static void myobject_listen_worker(QIOTask *task,
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* gpointer opaque)
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* {
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* QMyObject obj = QMY_OBJECT(qio_task_get_source(task));
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* SocketAddress *addr = opaque;
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* Error *err = NULL;
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*
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* obj->fd = socket_listen(addr, &err);
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*
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qio_task_set_error(task, err);
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* }
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*
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* void myobject_listen_async(QMyObject *obj,
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* SocketAddress *addr,
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* QIOTaskFunc *func,
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* gpointer opaque,
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* GDestroyNotify notify)
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* {
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* QIOTask *task;
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* SocketAddress *addrCopy;
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*
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* addrCopy = QAPI_CLONE(SocketAddress, addr);
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* task = qio_task_new(OBJECT(obj), func, opaque, notify);
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*
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* qio_task_run_in_thread(task, myobject_listen_worker,
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* addrCopy,
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* qapi_free_SocketAddress);
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* }
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* </example>
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*
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* NB, The 'func' callback passed into myobject_listen_async
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* will be invoked from the main event thread, despite the
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* actual operation being performed in a different thread.
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*/
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/**
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* qio_task_new:
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* @source: the object on which the operation is invoked
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* @func: the callback to invoke when the task completes
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* @opaque: opaque data to pass to @func when invoked
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* @destroy: optional callback to free @opaque
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*
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* Creates a new task struct to track completion of a
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* background operation running on the object @source.
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* When the operation completes or fails, the callback
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* @func will be invoked. The callback can access the
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* 'err' attribute in the task object to determine if
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* the operation was successful or not.
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*
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* The returned task will be released when qio_task_complete()
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* is invoked.
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*
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* Returns: the task struct
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*/
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QIOTask *qio_task_new(Object *source,
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QIOTaskFunc func,
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gpointer opaque,
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GDestroyNotify destroy);
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/**
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* qio_task_run_in_thread:
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* @task: the task struct
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* @worker: the function to invoke in a thread
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* @opaque: opaque data to pass to @worker
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* @destroy: function to free @opaque
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* @context: the context to run the complete hook. If %NULL, the
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* default context will be used.
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*
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* Run a task in a background thread. When @worker
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* returns it will call qio_task_complete() in
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* the event thread context that provided.
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*/
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void qio_task_run_in_thread(QIOTask *task,
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QIOTaskWorker worker,
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gpointer opaque,
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GDestroyNotify destroy,
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GMainContext *context);
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/**
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* qio_task_complete:
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* @task: the task struct
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*
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* Invoke the completion callback for @task and
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* then free its memory.
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*/
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void qio_task_complete(QIOTask *task);
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/**
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* qio_task_set_error:
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* @task: the task struct
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* @err: pointer to the error, or NULL
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*
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* Associate an error with the task, which can later
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* be retrieved with the qio_task_propagate_error()
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* method. This method takes ownership of @err, so
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* it is not valid to access it after this call
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* completes. If @err is NULL this is a no-op. If
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* this is call multiple times, only the first
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* provided @err will be recorded, later ones will
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* be discarded and freed.
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*/
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void qio_task_set_error(QIOTask *task,
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Error *err);
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/**
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* qio_task_propagate_error:
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* @task: the task struct
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* @errp: pointer to a NULL-initialized error object
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*
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* Propagate the error associated with @task
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* into @errp.
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*
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* Returns: true if an error was propagated, false otherwise
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*/
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bool qio_task_propagate_error(QIOTask *task,
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Error **errp);
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/**
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* qio_task_set_result_pointer:
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* @task: the task struct
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* @result: pointer to the result data
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*
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* Associate an opaque result with the task,
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* which can later be retrieved with the
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* qio_task_get_result_pointer() method
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*
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*/
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void qio_task_set_result_pointer(QIOTask *task,
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gpointer result,
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GDestroyNotify notify);
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/**
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* qio_task_get_result_pointer:
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* @task: the task struct
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*
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* Retrieve the opaque result data associated
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* with the task, if any.
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*
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* Returns: the task result, or NULL
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*/
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gpointer qio_task_get_result_pointer(QIOTask *task);
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/**
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* qio_task_get_source:
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* @task: the task struct
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*
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* Get the source object associated with the background
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* task. The caller does not own a reference on the
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* returned Object, and so should call object_ref()
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* if it wants to keep the object pointer outside the
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* lifetime of the QIOTask object.
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*
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* Returns: the source object
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*/
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Object *qio_task_get_source(QIOTask *task);
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#endif /* QIO_TASK_H */
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