/*
* 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 2.1 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
typedef struct QIOTask QIOTask;
typedef void (*QIOTaskFunc)(QIOTask *task,
gpointer opaque);
typedef void (*QIOTaskWorker)(QIOTask *task,
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 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.
*
* When the operation completes, the 'func' callback will be
* invoked, allowing the calling code to determine the result
* of the operation. An example QIOTaskFunc implementation may
* look like
*
* <example>
* <title>Task callback implementation</title>
* <programlisting>
* static void myobject_operation_notify(QIOTask *task,
* gpointer opaque)
* {
* Error *err = NULL;
* if (qio_task_propagate_error(task, &err)) {
* ...deal with the failure...
* error_free(err);
* } else {
* QMyObject *src = QMY_OBJECT(qio_task_get_source(task));
* ...deal with the completion...
* }
* }
* </programlisting>
* </example>
*
* Now, lets say the implementation of the method using the
* task wants to set a timer to run once a second checking
* for completion of some activity. It would do something
* like
*
* <example>
* <title>Task 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 = NULL;
*
* ...check something important...
* if (err) {
* qio_task_set_error(task, err);
* qio_task_complete(task);
* return FALSE;
* } else if (...work is completed ...) {
* qio_task_complete(task);
* return FALSE;
* }
* ...carry on polling ...
* return TRUE;
* }
* </programlisting>
* </example>
*
* The 'qio_task_complete' call in this method will trigger
* the callback func 'myobject_operation_notify' shown
* earlier to deal with the results.
*
* 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 void myobject_listen_worker(QIOTask *task,
* gpointer opaque)
* {
* QMyObject obj = QMY_OBJECT(qio_task_get_source(task));
* SocketAddress *addr = opaque;
* Error *err = NULL;
*
* obj->fd = socket_listen(addr, &err);
*
qio_task_set_error(task, err);
* }
*
* void myobject_listen_async(QMyObject *obj,
* SocketAddress *addr,
* QIOTaskFunc *func,
* gpointer opaque,
* GDestroyNotify notify)
* {
* QIOTask *task;
* SocketAddress *addrCopy;
*
* addrCopy = QAPI_CLONE(SocketAddress, 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 qio_task_complete()
* is 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
* @context: the context to run the complete hook. If %NULL, the
* default context will be used.
*
* Run a task in a background thread. When @worker
* returns it will call qio_task_complete() in
* the thread that is running the main loop associated
* with @context.
*/
void qio_task_run_in_thread(QIOTask *task,
QIOTaskWorker worker,
gpointer opaque,
GDestroyNotify destroy,
GMainContext *context);
/**
* qio_task_wait_thread:
* @task: the task struct
*
* Wait for completion of a task that was previously
* invoked using qio_task_run_in_thread. This MUST
* ONLY be invoked if the task has not already
* completed, since after the completion callback
* is invoked, @task will have been freed.
*
* To avoid racing with execution of the completion
* callback provided with qio_task_new, this method
* MUST ONLY be invoked from the thread that is
* running the main loop associated with @context
* parameter to qio_task_run_in_thread.
*
* When the thread has completed, the completion
* callback provided to qio_task_new will be invoked.
* When that callback returns @task will be freed,
* so @task must not be referenced after this
* method completes.
*/
void qio_task_wait_thread(QIOTask *task);
/**
* qio_task_complete:
* @task: the task struct
*
* Invoke the completion callback for @task and
* then free its memory.
*/
void qio_task_complete(QIOTask *task);
/**
* qio_task_set_error:
* @task: the task struct
* @err: pointer to the error, or NULL
*
* Associate an error with the task, which can later
* be retrieved with the qio_task_propagate_error()
* method. This method takes ownership of @err, so
* it is not valid to access it after this call
* completes. If @err is NULL this is a no-op. If
* this is call multiple times, only the first
* provided @err will be recorded, later ones will
* be discarded and freed.
*/
void qio_task_set_error(QIOTask *task,
Error *err);
/**
* qio_task_propagate_error:
* @task: the task struct
* @errp: pointer to a NULL-initialized error object
*
* Propagate the error associated with @task
* into @errp.
*
* Returns: true if an error was propagated, false otherwise
*/
bool qio_task_propagate_error(QIOTask *task,
Error **errp);
/**
* qio_task_set_result_pointer:
* @task: the task struct
* @result: pointer to the result data
*
* Associate an opaque result with the task,
* which can later be retrieved with the
* qio_task_get_result_pointer() method
*
*/
void qio_task_set_result_pointer(QIOTask *task,
gpointer result,
GDestroyNotify notify);
/**
* qio_task_get_result_pointer:
* @task: the task struct
*
* Retrieve the opaque result data associated
* with the task, if any.
*
* Returns: the task result, or NULL
*/
gpointer qio_task_get_result_pointer(QIOTask *task);
/**
* qio_task_get_source:
* @task: the task struct
*
* Get the source object associated with the background
* task. The caller does not own a reference on the
* returned Object, and so should call object_ref()
* if it wants to keep the object pointer outside the
* lifetime of the QIOTask object.
*
* Returns: the source object
*/
Object *qio_task_get_source(QIOTask *task);
#endif /* QIO_TASK_H */
