Daniel P. Berrange | b02db2d | 2015-03-18 17:25:45 +0000 | [diff] [blame] | 1 | /* |
| 2 | * QEMU I/O task |
| 3 | * |
| 4 | * Copyright (c) 2015 Red Hat, Inc. |
| 5 | * |
| 6 | * This library is free software; you can redistribute it and/or |
| 7 | * modify it under the terms of the GNU Lesser General Public |
| 8 | * License as published by the Free Software Foundation; either |
| 9 | * version 2 of the License, or (at your option) any later version. |
| 10 | * |
| 11 | * This library is distributed in the hope that it will be useful, |
| 12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 14 | * Lesser General Public License for more details. |
| 15 | * |
| 16 | * You should have received a copy of the GNU Lesser General Public |
| 17 | * License along with this library; if not, see <http://www.gnu.org/licenses/>. |
| 18 | * |
| 19 | */ |
| 20 | |
| 21 | #ifndef QIO_TASK_H__ |
| 22 | #define QIO_TASK_H__ |
| 23 | |
| 24 | #include "qemu-common.h" |
Daniel P. Berrange | b02db2d | 2015-03-18 17:25:45 +0000 | [diff] [blame] | 25 | #include "qom/object.h" |
| 26 | |
| 27 | typedef struct QIOTask QIOTask; |
| 28 | |
| 29 | typedef void (*QIOTaskFunc)(Object *source, |
| 30 | Error *err, |
| 31 | gpointer opaque); |
| 32 | |
| 33 | typedef int (*QIOTaskWorker)(QIOTask *task, |
| 34 | Error **errp, |
| 35 | gpointer opaque); |
| 36 | |
| 37 | /** |
| 38 | * QIOTask: |
| 39 | * |
| 40 | * The QIOTask object provides a simple mechanism for reporting |
| 41 | * success / failure of long running background operations. |
| 42 | * |
| 43 | * A object on which the operation is to be performed could have |
| 44 | * a public API which accepts a task callback: |
| 45 | * |
| 46 | * <example> |
| 47 | * <title>Task callback function signature</title> |
| 48 | * <programlisting> |
| 49 | * void myobject_operation(QMyObject *obj, |
| 50 | * QIOTaskFunc *func, |
| 51 | * gpointer opaque, |
| 52 | * GDestroyNotify *notify); |
| 53 | * </programlisting> |
| 54 | * </example> |
| 55 | * |
| 56 | * The 'func' parameter is the callback to be invoked, and 'opaque' |
| 57 | * is data to pass to it. The optional 'notify' function is used |
| 58 | * to free 'opaque' when no longer needed. |
| 59 | * |
| 60 | * Now, lets say the implementation of this method wants to set |
| 61 | * a timer to run once a second checking for completion of some |
| 62 | * activity. It would do something like |
| 63 | * |
| 64 | * <example> |
| 65 | * <title>Task callback function implementation</title> |
| 66 | * <programlisting> |
| 67 | * void myobject_operation(QMyObject *obj, |
| 68 | * QIOTaskFunc *func, |
| 69 | * gpointer opaque, |
| 70 | * GDestroyNotify *notify) |
| 71 | * { |
| 72 | * QIOTask *task; |
| 73 | * |
| 74 | * task = qio_task_new(OBJECT(obj), func, opaque, notify); |
| 75 | * |
| 76 | * g_timeout_add_full(G_PRIORITY_DEFAULT, |
| 77 | * 1000, |
| 78 | * myobject_operation_timer, |
| 79 | * task, |
| 80 | * NULL); |
| 81 | * } |
| 82 | * </programlisting> |
| 83 | * </example> |
| 84 | * |
| 85 | * It could equally have setup a watch on a file descriptor or |
| 86 | * created a background thread, or something else entirely. |
| 87 | * Notice that the source object is passed to the task, and |
| 88 | * QIOTask will hold a reference on that. This ensure that |
| 89 | * the QMyObject instance cannot be garbage collected while |
| 90 | * the async task is still in progress. |
| 91 | * |
| 92 | * In this case, myobject_operation_timer will fire after |
| 93 | * 3 secs and do |
| 94 | * |
| 95 | * <example> |
| 96 | * <title>Task timer function</title> |
| 97 | * <programlisting> |
| 98 | * gboolean myobject_operation_timer(gpointer opaque) |
| 99 | * { |
| 100 | * QIOTask *task = QIO_TASK(opaque); |
| 101 | * Error *err;* |
| 102 | * |
| 103 | * ...check something important... |
| 104 | * if (err) { |
| 105 | * qio_task_abort(task, err); |
| 106 | * error_free(task); |
| 107 | * return FALSE; |
| 108 | * } else if (...work is completed ...) { |
| 109 | * qio_task_complete(task); |
| 110 | * return FALSE; |
| 111 | * } |
| 112 | * ...carry on polling ... |
| 113 | * return TRUE; |
| 114 | * } |
| 115 | * </programlisting> |
| 116 | * </example> |
| 117 | * |
| 118 | * Once this function returns false, object_unref will be called |
| 119 | * automatically on the task causing it to be released and the |
| 120 | * ref on QMyObject dropped too. |
| 121 | * |
| 122 | * The QIOTask module can also be used to perform operations |
| 123 | * in a background thread context, while still reporting the |
| 124 | * results in the main event thread. This allows code which |
| 125 | * cannot easily be rewritten to be asychronous (such as DNS |
| 126 | * lookups) to be easily run non-blocking. Reporting the |
| 127 | * results in the main thread context means that the caller |
| 128 | * typically does not need to be concerned about thread |
| 129 | * safety wrt the QEMU global mutex. |
| 130 | * |
| 131 | * For example, the socket_listen() method will block the caller |
| 132 | * while DNS lookups take place if given a name, instead of IP |
| 133 | * address. The C library often do not provide a practical async |
| 134 | * DNS API, so the to get non-blocking DNS lookups in a portable |
| 135 | * manner requires use of a thread. So achieve a non-blocking |
| 136 | * socket listen using QIOTask would require: |
| 137 | * |
| 138 | * <example> |
| 139 | * static int myobject_listen_worker(QIOTask *task, |
| 140 | * Error **errp, |
| 141 | * gpointer opaque) |
| 142 | * { |
| 143 | * QMyObject obj = QMY_OBJECT(qio_task_get_source(task)); |
| 144 | * SocketAddress *addr = opaque; |
| 145 | * |
| 146 | * obj->fd = socket_listen(addr, errp); |
| 147 | * if (obj->fd < 0) { |
| 148 | * return -1; |
| 149 | * } |
| 150 | * return 0; |
| 151 | * } |
| 152 | * |
| 153 | * void myobject_listen_async(QMyObject *obj, |
| 154 | * SocketAddress *addr, |
| 155 | * QIOTaskFunc *func, |
| 156 | * gpointer opaque, |
| 157 | * GDestroyNotify *notify) |
| 158 | * { |
| 159 | * QIOTask *task; |
| 160 | * SocketAddress *addrCopy; |
| 161 | * |
| 162 | * qapi_copy_SocketAddress(&addrCopy, addr); |
| 163 | * task = qio_task_new(OBJECT(obj), func, opaque, notify); |
| 164 | * |
| 165 | * qio_task_run_in_thread(task, myobject_listen_worker, |
| 166 | * addrCopy, |
| 167 | * qapi_free_SocketAddress); |
| 168 | * } |
| 169 | * </example> |
| 170 | * |
| 171 | * NB, The 'func' callback passed into myobject_listen_async |
| 172 | * will be invoked from the main event thread, despite the |
| 173 | * actual operation being performed in a different thread. |
| 174 | */ |
| 175 | |
| 176 | /** |
| 177 | * qio_task_new: |
| 178 | * @source: the object on which the operation is invoked |
| 179 | * @func: the callback to invoke when the task completes |
| 180 | * @opaque: opaque data to pass to @func when invoked |
| 181 | * @destroy: optional callback to free @opaque |
| 182 | * |
| 183 | * Creates a new task struct to track completion of a |
| 184 | * background operation running on the object @source. |
| 185 | * When the operation completes or fails, the callback |
| 186 | * @func will be invoked. The callback can access the |
| 187 | * 'err' attribute in the task object to determine if |
| 188 | * the operation was successful or not. |
| 189 | * |
| 190 | * The returned task will be released when one of |
| 191 | * qio_task_abort() or qio_task_complete() are invoked. |
| 192 | * |
| 193 | * Returns: the task struct |
| 194 | */ |
| 195 | QIOTask *qio_task_new(Object *source, |
| 196 | QIOTaskFunc func, |
| 197 | gpointer opaque, |
| 198 | GDestroyNotify destroy); |
| 199 | |
| 200 | /** |
| 201 | * qio_task_run_in_thread: |
| 202 | * @task: the task struct |
| 203 | * @worker: the function to invoke in a thread |
| 204 | * @opaque: opaque data to pass to @worker |
| 205 | * @destroy: function to free @opaque |
| 206 | * |
| 207 | * Run a task in a background thread. If @worker |
| 208 | * returns 0 it will call qio_task_complete() in |
| 209 | * the main event thread context. If @worker |
| 210 | * returns -1 it will call qio_task_abort() in |
| 211 | * the main event thread context. |
| 212 | */ |
| 213 | void qio_task_run_in_thread(QIOTask *task, |
| 214 | QIOTaskWorker worker, |
| 215 | gpointer opaque, |
| 216 | GDestroyNotify destroy); |
| 217 | |
| 218 | /** |
| 219 | * qio_task_complete: |
| 220 | * @task: the task struct |
| 221 | * |
| 222 | * Mark the operation as succesfully completed |
| 223 | * and free the memory for @task. |
| 224 | */ |
| 225 | void qio_task_complete(QIOTask *task); |
| 226 | |
| 227 | /** |
| 228 | * qio_task_abort: |
| 229 | * @task: the task struct |
| 230 | * @err: the error to record for the operation |
| 231 | * |
| 232 | * Mark the operation as failed, with @err providing |
| 233 | * details about the failure. The @err may be freed |
| 234 | * afer the function returns, as the notification |
| 235 | * callback is invoked synchronously. The @task will |
| 236 | * be freed when this call completes. |
| 237 | */ |
| 238 | void qio_task_abort(QIOTask *task, |
| 239 | Error *err); |
| 240 | |
| 241 | |
| 242 | /** |
| 243 | * qio_task_get_source: |
| 244 | * @task: the task struct |
| 245 | * |
| 246 | * Get the source object associated with the background |
| 247 | * task. This returns a new reference to the object, |
| 248 | * which the caller must released with object_unref() |
| 249 | * when no longer required. |
| 250 | * |
| 251 | * Returns: the source object |
| 252 | */ |
| 253 | Object *qio_task_get_source(QIOTask *task); |
| 254 | |
| 255 | #endif /* QIO_TASK_H__ */ |