diff --git a/gio/gtask.c b/gio/gtask.c index dc2394f44..30bb007f2 100644 --- a/gio/gtask.c +++ b/gio/gtask.c @@ -30,29 +30,27 @@ * @include: gio/gio.h * @see_also: #GAsyncResult * - * - * A #GTask represents and manages a cancellable "task". - * - * - * Asynchronous operations - * - * The most common usage of #GTask is as a #GAsyncResult, to - * manage data during an asynchronous operation. You call - * g_task_new() in the "start" method, followed by - * g_task_set_task_data() and the like if you need to keep some - * additional data associated with the task, and then pass the - * task object around through your asynchronous operation. - * Eventually, you will call a method such as - * g_task_return_pointer() or g_task_return_error(), which will - * save the value you give it and then invoke the task's callback - * function (waiting until the next iteration of the main - * loop first, if necessary). The caller will pass the #GTask back - * to the operation's finish function (as a #GAsyncResult), and - * you can use g_task_propagate_pointer() or the like to extract - * the return value. - * - * Here is an example for using GTask as a GAsyncResult: - * |[ + * A #GTask represents and manages a cancellable "task". + * + * ## Asynchronous operations + * + * The most common usage of #GTask is as a #GAsyncResult, to + * manage data during an asynchronous operation. You call + * g_task_new() in the "start" method, followed by + * g_task_set_task_data() and the like if you need to keep some + * additional data associated with the task, and then pass the + * task object around through your asynchronous operation. + * Eventually, you will call a method such as + * g_task_return_pointer() or g_task_return_error(), which will + * save the value you give it and then invoke the task's callback + * function (waiting until the next iteration of the main + * loop first, if necessary). The caller will pass the #GTask back + * to the operation's finish function (as a #GAsyncResult), and + * you can use g_task_propagate_pointer() or the like to extract + * the return value. + * + * Here is an example for using GTask as a GAsyncResult: + * |[ * typedef struct { * CakeFrostingType frosting; * char *message; @@ -145,23 +143,21 @@ * return g_task_propagate_pointer (G_TASK (result), error); * } * ]| - * - * - * Chained asynchronous operations - * - * #GTask also tries to simplify asynchronous operations that - * internally chain together several smaller asynchronous - * operations. g_task_get_cancellable(), g_task_get_context(), and - * g_task_get_priority() allow you to get back the task's - * #GCancellable, #GMainContext, and I/O priority when starting a new - * subtask, so you don't have to keep track of them yourself. - * g_task_attach_source() simplifies the case of waiting for a - * source to fire (automatically using the correct #GMainContext - * and priority). - * - * - * Here is an example for chained asynchronous operations: + * + * ## Chained asynchronous operations + * + * #GTask also tries to simplify asynchronous operations that + * internally chain together several smaller asynchronous + * operations. g_task_get_cancellable(), g_task_get_context(), and + * g_task_get_priority() allow you to get back the task's + * #GCancellable, #GMainContext, and I/O priority when starting a new + * subtask, so you don't have to keep track of them yourself. + * g_task_attach_source() simplifies the case of waiting for a + * source to fire (automatically using the correct #GMainContext + * and priority). + * + * Here is an example for chained asynchronous operations: * |[ * typedef struct { * Cake *cake; @@ -288,18 +284,15 @@ * return g_task_propagate_pointer (G_TASK (result), error); * } * ]| - * - * - * - * Asynchronous operations from synchronous ones - * - * You can use g_task_run_in_thread() to turn a synchronous - * operation into an asynchronous one, by running it in a thread - * which will then dispatch the result back to the caller's - * #GMainContext when it completes. - * - * - * Running a task in a thread: + * + * ## Asynchronous operations from synchronous ones + * + * You can use g_task_run_in_thread() to turn a synchronous + * operation into an asynchronous one, by running it in a thread + * which will then dispatch the result back to the caller's + * #GMainContext when it completes. + * + * Running a task in a thread: * |[ * typedef struct { * guint radius; @@ -368,25 +361,22 @@ * return g_task_propagate_pointer (G_TASK (result), error); * } * ]| - * - * - * - * Adding cancellability to uncancellable tasks - * - * Finally, g_task_run_in_thread() and g_task_run_in_thread_sync() - * can be used to turn an uncancellable operation into a - * cancellable one. If you call g_task_set_return_on_cancel(), - * passing %TRUE, then if the task's #GCancellable is cancelled, - * it will return control back to the caller immediately, while - * allowing the task thread to continue running in the background - * (and simply discarding its result when it finally does finish). - * Provided that the task thread is careful about how it uses - * locks and other externally-visible resources, this allows you - * to make "GLib-friendly" asynchronous and cancellable - * synchronous variants of blocking APIs. - * - * - * Cancelling a task: + * + * ## Adding cancellability to uncancellable tasks + * + * Finally, g_task_run_in_thread() and g_task_run_in_thread_sync() + * can be used to turn an uncancellable operation into a + * cancellable one. If you call g_task_set_return_on_cancel(), + * passing %TRUE, then if the task's #GCancellable is cancelled, + * it will return control back to the caller immediately, while + * allowing the task thread to continue running in the background + * (and simply discarding its result when it finally does finish). + * Provided that the task thread is careful about how it uses + * locks and other externally-visible resources, this allows you + * to make "GLib-friendly" asynchronous and cancellable + * synchronous variants of blocking APIs. + * + * Cancelling a task: * |[ * static void * bake_cake_thread (GTask *task, @@ -439,7 +429,7 @@ * GAsyncReadyCallback callback, * gpointer user_data) * { - * CakeData *cake_data; + J* CakeData *cake_data; * GTask *task; * * cake_data = g_slice_new (CakeData); @@ -477,80 +467,62 @@ * return cake; * } * ]| - * - * - * - * Porting from <literal>GSimpleAsyncResult</literal> - * - * #GTask's API attempts to be simpler than #GSimpleAsyncResult's - * in several ways: - * - * - * - * You can save task-specific data with g_task_set_task_data(), and - * retrieve it later with g_task_get_task_data(). This replaces the - * abuse of g_simple_async_result_set_op_res_gpointer() for the same - * purpose with #GSimpleAsyncResult. - * - * - * In addition to the task data, #GTask also keeps track of the - * priority, #GCancellable, and - * #GMainContext associated with the task, so tasks that consist of - * a chain of simpler asynchronous operations will have easy access - * to those values when starting each sub-task. - * - * - * g_task_return_error_if_cancelled() provides simplified - * handling for cancellation. In addition, cancellation - * overrides any other #GTask return value by default, like - * #GSimpleAsyncResult does when - * g_simple_async_result_set_check_cancellable() is called. - * (You can use g_task_set_check_cancellable() to turn off that - * behavior.) On the other hand, g_task_run_in_thread() - * guarantees that it will always run your - * task_func, even if the task's #GCancellable - * is already cancelled before the task gets a chance to run; - * you can start your task_func with a - * g_task_return_error_if_cancelled() check if you need the - * old behavior. - * - * - * The "return" methods (eg, g_task_return_pointer()) - * automatically cause the task to be "completed" as well, and - * there is no need to worry about the "complete" vs "complete - * in idle" distinction. (#GTask automatically figures out - * whether the task's callback can be invoked directly, or - * if it needs to be sent to another #GMainContext, or delayed - * until the next iteration of the current #GMainContext.) - * - * - * The "finish" functions for #GTask-based operations are generally - * much simpler than #GSimpleAsyncResult ones, normally consisting - * of only a single call to g_task_propagate_pointer() or the like. - * Since g_task_propagate_pointer() "steals" the return value from - * the #GTask, it is not necessary to juggle pointers around to - * prevent it from being freed twice. - * - * - * With #GSimpleAsyncResult, it was common to call - * g_simple_async_result_propagate_error() from the - * _finish() wrapper function, and have - * virtual method implementations only deal with successful - * returns. This behavior is deprecated, because it makes it - * difficult for a subclass to chain to a parent class's async - * methods. Instead, the wrapper function should just be a - * simple wrapper, and the virtual method should call an - * appropriate g_task_propagate_ function. - * Note that wrapper methods can now use - * g_async_result_legacy_propagate_error() to do old-style - * #GSimpleAsyncResult error-returning behavior, and - * g_async_result_is_tagged() to check if a result is tagged as - * having come from the _async() wrapper - * function (for "short-circuit" results, such as when passing - * 0 to g_input_stream_read_async()). - * - * - * + * + * ## Porting from GSimpleAsyncResult + * + * #GTask's API attempts to be simpler than #GSimpleAsyncResult's + * in several ways: + * - You can save task-specific data with g_task_set_task_data(), and + * retrieve it later with g_task_get_task_data(). This replaces the + * abuse of g_simple_async_result_set_op_res_gpointer() for the same + * purpose with #GSimpleAsyncResult. + * - In addition to the task data, #GTask also keeps track of the + * priority, #GCancellable, and + * #GMainContext associated with the task, so tasks that consist of + * a chain of simpler asynchronous operations will have easy access + * to those values when starting each sub-task. + * - g_task_return_error_if_cancelled() provides simplified + * handling for cancellation. In addition, cancellation + * overrides any other #GTask return value by default, like + * #GSimpleAsyncResult does when + * g_simple_async_result_set_check_cancellable() is called. + * (You can use g_task_set_check_cancellable() to turn off that + * behavior.) On the other hand, g_task_run_in_thread() + * guarantees that it will always run your + * task_func, even if the task's #GCancellable + * is already cancelled before the task gets a chance to run; + * you can start your task_func with a + * g_task_return_error_if_cancelled() check if you need the + * old behavior. + * - The "return" methods (eg, g_task_return_pointer()) + * automatically cause the task to be "completed" as well, and + * there is no need to worry about the "complete" vs "complete + * in idle" distinction. (#GTask automatically figures out + * whether the task's callback can be invoked directly, or + * if it needs to be sent to another #GMainContext, or delayed + * until the next iteration of the current #GMainContext.) + * - The "finish" functions for #GTask-based operations are generally + * much simpler than #GSimpleAsyncResult ones, normally consisting + * of only a single call to g_task_propagate_pointer() or the like. + * Since g_task_propagate_pointer() "steals" the return value from + * the #GTask, it is not necessary to juggle pointers around to + * prevent it from being freed twice. + * - With #GSimpleAsyncResult, it was common to call + * g_simple_async_result_propagate_error() from the + * _finish() wrapper function, and have + * virtual method implementations only deal with successful + * returns. This behavior is deprecated, because it makes it + * difficult for a subclass to chain to a parent class's async + * methods. Instead, the wrapper function should just be a + * simple wrapper, and the virtual method should call an + * appropriate g_task_propagate_ function. + * Note that wrapper methods can now use + * g_async_result_legacy_propagate_error() to do old-style + * #GSimpleAsyncResult error-returning behavior, and + * g_async_result_is_tagged() to check if a result is tagged as + * having come from the _async() wrapper + * function (for "short-circuit" results, such as when passing + * 0 to g_input_stream_read_async()). */ /**