mirror of https://gitee.com/openkylin/qemu.git
256 lines
8.2 KiB
C
256 lines
8.2 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)(Object *source,
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Error *err,
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gpointer opaque);
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typedef int (*QIOTaskWorker)(QIOTask *task,
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Error **errp,
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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 callback 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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* Now, lets say the implementation of this method wants to set
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* a timer to run once a second checking for completion of some
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* activity. It would do something like
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*
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* <example>
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* <title>Task callback 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_abort(task, err);
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* error_free(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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* 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 int myobject_listen_worker(QIOTask *task,
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* Error **errp,
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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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*
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* obj->fd = socket_listen(addr, errp);
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* if (obj->fd < 0) {
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* return -1;
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* }
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* return 0;
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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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* qapi_copy_SocketAddress(&addrCopy, 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 one of
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* qio_task_abort() or qio_task_complete() are 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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*
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* Run a task in a background thread. If @worker
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* returns 0 it will call qio_task_complete() in
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* the main event thread context. If @worker
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* returns -1 it will call qio_task_abort() in
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* the main event thread context.
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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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/**
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* qio_task_complete:
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* @task: the task struct
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*
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* Mark the operation as successfully completed
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* and free the memory for @task.
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*/
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void qio_task_complete(QIOTask *task);
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/**
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* qio_task_abort:
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* @task: the task struct
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* @err: the error to record for the operation
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*
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* Mark the operation as failed, with @err providing
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* details about the failure. The @err may be freed
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* afer the function returns, as the notification
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* callback is invoked synchronously. The @task will
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* be freed when this call completes.
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*/
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void qio_task_abort(QIOTask *task,
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Error *err);
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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. This returns a new reference to the object,
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* which the caller must released with object_unref()
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* when no longer required.
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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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