| /* |
| * QEMU I/O task |
| * |
| * Copyright (c) 2015 Red Hat, Inc. |
| * |
| * This library is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU Lesser General Public |
| * License as published by the Free Software Foundation; either |
| * version 2 of the License, or (at your option) any later version. |
| * |
| * This library is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| * Lesser General Public License for more details. |
| * |
| * You should have received a copy of the GNU Lesser General Public |
| * License along with this library; if not, see <http://www.gnu.org/licenses/>. |
| * |
| */ |
| |
| #ifndef QIO_TASK_H__ |
| #define QIO_TASK_H__ |
| |
| #include "qemu-common.h" |
| #include "qapi/error.h" |
| #include "qom/object.h" |
| |
| typedef struct QIOTask QIOTask; |
| |
| typedef void (*QIOTaskFunc)(Object *source, |
| Error *err, |
| gpointer opaque); |
| |
| typedef int (*QIOTaskWorker)(QIOTask *task, |
| Error **errp, |
| gpointer opaque); |
| |
| /** |
| * QIOTask: |
| * |
| * The QIOTask object provides a simple mechanism for reporting |
| * success / failure of long running background operations. |
| * |
| * A object on which the operation is to be performed could have |
| * a public API which accepts a task callback: |
| * |
| * <example> |
| * <title>Task callback function signature</title> |
| * <programlisting> |
| * void myobject_operation(QMyObject *obj, |
| * QIOTaskFunc *func, |
| * gpointer opaque, |
| * GDestroyNotify *notify); |
| * </programlisting> |
| * </example> |
| * |
| * The 'func' parameter is the callback to be invoked, and 'opaque' |
| * is data to pass to it. The optional 'notify' function is used |
| * to free 'opaque' when no longer needed. |
| * |
| * Now, lets say the implementation of this method wants to set |
| * a timer to run once a second checking for completion of some |
| * activity. It would do something like |
| * |
| * <example> |
| * <title>Task callback function implementation</title> |
| * <programlisting> |
| * void myobject_operation(QMyObject *obj, |
| * QIOTaskFunc *func, |
| * gpointer opaque, |
| * GDestroyNotify *notify) |
| * { |
| * QIOTask *task; |
| * |
| * task = qio_task_new(OBJECT(obj), func, opaque, notify); |
| * |
| * g_timeout_add_full(G_PRIORITY_DEFAULT, |
| * 1000, |
| * myobject_operation_timer, |
| * task, |
| * NULL); |
| * } |
| * </programlisting> |
| * </example> |
| * |
| * It could equally have setup a watch on a file descriptor or |
| * created a background thread, or something else entirely. |
| * Notice that the source object is passed to the task, and |
| * QIOTask will hold a reference on that. This ensure that |
| * the QMyObject instance cannot be garbage collected while |
| * the async task is still in progress. |
| * |
| * In this case, myobject_operation_timer will fire after |
| * 3 secs and do |
| * |
| * <example> |
| * <title>Task timer function</title> |
| * <programlisting> |
| * gboolean myobject_operation_timer(gpointer opaque) |
| * { |
| * QIOTask *task = QIO_TASK(opaque); |
| * Error *err;* |
| * |
| * ...check something important... |
| * if (err) { |
| * qio_task_abort(task, err); |
| * error_free(task); |
| * return FALSE; |
| * } else if (...work is completed ...) { |
| * qio_task_complete(task); |
| * return FALSE; |
| * } |
| * ...carry on polling ... |
| * return TRUE; |
| * } |
| * </programlisting> |
| * </example> |
| * |
| * Once this function returns false, object_unref will be called |
| * automatically on the task causing it to be released and the |
| * ref on QMyObject dropped too. |
| * |
| * The QIOTask module can also be used to perform operations |
| * in a background thread context, while still reporting the |
| * results in the main event thread. This allows code which |
| * cannot easily be rewritten to be asychronous (such as DNS |
| * lookups) to be easily run non-blocking. Reporting the |
| * results in the main thread context means that the caller |
| * typically does not need to be concerned about thread |
| * safety wrt the QEMU global mutex. |
| * |
| * For example, the socket_listen() method will block the caller |
| * while DNS lookups take place if given a name, instead of IP |
| * address. The C library often do not provide a practical async |
| * DNS API, so the to get non-blocking DNS lookups in a portable |
| * manner requires use of a thread. So achieve a non-blocking |
| * socket listen using QIOTask would require: |
| * |
| * <example> |
| * static int myobject_listen_worker(QIOTask *task, |
| * Error **errp, |
| * gpointer opaque) |
| * { |
| * QMyObject obj = QMY_OBJECT(qio_task_get_source(task)); |
| * SocketAddress *addr = opaque; |
| * |
| * obj->fd = socket_listen(addr, errp); |
| * if (obj->fd < 0) { |
| * return -1; |
| * } |
| * return 0; |
| * } |
| * |
| * void myobject_listen_async(QMyObject *obj, |
| * SocketAddress *addr, |
| * QIOTaskFunc *func, |
| * gpointer opaque, |
| * GDestroyNotify *notify) |
| * { |
| * QIOTask *task; |
| * SocketAddress *addrCopy; |
| * |
| * qapi_copy_SocketAddress(&addrCopy, addr); |
| * task = qio_task_new(OBJECT(obj), func, opaque, notify); |
| * |
| * qio_task_run_in_thread(task, myobject_listen_worker, |
| * addrCopy, |
| * qapi_free_SocketAddress); |
| * } |
| * </example> |
| * |
| * NB, The 'func' callback passed into myobject_listen_async |
| * will be invoked from the main event thread, despite the |
| * actual operation being performed in a different thread. |
| */ |
| |
| /** |
| * qio_task_new: |
| * @source: the object on which the operation is invoked |
| * @func: the callback to invoke when the task completes |
| * @opaque: opaque data to pass to @func when invoked |
| * @destroy: optional callback to free @opaque |
| * |
| * Creates a new task struct to track completion of a |
| * background operation running on the object @source. |
| * When the operation completes or fails, the callback |
| * @func will be invoked. The callback can access the |
| * 'err' attribute in the task object to determine if |
| * the operation was successful or not. |
| * |
| * The returned task will be released when one of |
| * qio_task_abort() or qio_task_complete() are invoked. |
| * |
| * Returns: the task struct |
| */ |
| QIOTask *qio_task_new(Object *source, |
| QIOTaskFunc func, |
| gpointer opaque, |
| GDestroyNotify destroy); |
| |
| /** |
| * qio_task_run_in_thread: |
| * @task: the task struct |
| * @worker: the function to invoke in a thread |
| * @opaque: opaque data to pass to @worker |
| * @destroy: function to free @opaque |
| * |
| * Run a task in a background thread. If @worker |
| * returns 0 it will call qio_task_complete() in |
| * the main event thread context. If @worker |
| * returns -1 it will call qio_task_abort() in |
| * the main event thread context. |
| */ |
| void qio_task_run_in_thread(QIOTask *task, |
| QIOTaskWorker worker, |
| gpointer opaque, |
| GDestroyNotify destroy); |
| |
| /** |
| * qio_task_complete: |
| * @task: the task struct |
| * |
| * Mark the operation as succesfully completed |
| * and free the memory for @task. |
| */ |
| void qio_task_complete(QIOTask *task); |
| |
| /** |
| * qio_task_abort: |
| * @task: the task struct |
| * @err: the error to record for the operation |
| * |
| * Mark the operation as failed, with @err providing |
| * details about the failure. The @err may be freed |
| * afer the function returns, as the notification |
| * callback is invoked synchronously. The @task will |
| * be freed when this call completes. |
| */ |
| void qio_task_abort(QIOTask *task, |
| Error *err); |
| |
| |
| /** |
| * qio_task_get_source: |
| * @task: the task struct |
| * |
| * Get the source object associated with the background |
| * task. This returns a new reference to the object, |
| * which the caller must released with object_unref() |
| * when no longer required. |
| * |
| * Returns: the source object |
| */ |
| Object *qio_task_get_source(QIOTask *task); |
| |
| #endif /* QIO_TASK_H__ */ |
