GLib.MainContext¶

Fields¶

None

Methods¶

class	`default` ()
class	`get_thread_default` ()
class	`new` ()
class	`new_with_flags` (flags)
class	`ref_thread_default` ()
	`acquire` ()
	`add_poll` (fd, priority)
	`check` (max_priority, fds)
	`dispatch` ()
	`find_source_by_funcs_user_data` (funcs, user_data)
	`find_source_by_id` (source_id)
	`find_source_by_user_data` (user_data)
	`invoke_full` (priority, function, *data)
	`is_owner` ()
	`iteration` (may_block)
	`pending` ()
	`pop_thread_default` ()
	`prepare` ()
	`push_thread_default` ()
	`pusher_new` ()
	`query` (max_priority)
	`ref` ()
	`release` ()
	`remove_poll` (fd)
	`unref` ()
	`wait` (cond, mutex)
	`wakeup` ()

Details¶

class GLib.MainContext¶

The GMainContext struct is an opaque data type representing a set of sources to be handled in a main loop.

classmethod default()[source]¶

Returns:: the global-default main context.
Return type:: GLib.MainContext

Returns the global-default main context. This is the main context used for main loop functions when a main loop is not explicitly specified, and corresponds to the “main” main loop. See also [func`GLib`.MainContext.get_thread_default].

classmethod get_thread_default()[source]¶

Returns:: the thread-default GLib.MainContext, or None if the thread-default context is the global-default main context.
Return type:: GLib.MainContext or None

Gets the thread-default GLib.MainContext for this thread. Asynchronous operations that want to be able to be run in contexts other than the default one should call this method or [func`GLib`.MainContext.ref_thread_default] to get a [struct`GLib`.MainContext] to add their [struct`GLib`.Source]s to. (Note that even in single-threaded programs applications may sometimes want to temporarily push a non-default context, so it is not safe to assume that this will always return None if you are running in the default thread.)

If you need to hold a reference on the context, use [func`GLib`.MainContext.ref_thread_default] instead.

New in version 2.22.

classmethod new()[source]¶

Returns:: the new GLib.MainContext
Return type:: GLib.MainContext

Creates a new [struct`GLib`.MainContext] structure.

classmethod new_with_flags(flags)[source]¶

Parameters:: flags (GLib.MainContextFlags) – a bitwise-OR combination of GLib.MainContextFlags flags that can only be set at creation time.
Returns:: the new GLib.MainContext
Return type:: GLib.MainContext

Creates a new [struct`GLib`.MainContext] structure.

New in version 2.72.

classmethod ref_thread_default()[source]¶

Returns:: the thread-default GLib.MainContext. Unref with [method`GLib`.MainContext.unref] when you are done with it.
Return type:: GLib.MainContext

Gets the thread-default [struct`GLib`.MainContext] for this thread, as with [func`GLib`.MainContext.get_thread_default], but also adds a reference to it with [method`GLib`.MainContext.ref]. In addition, unlike [func`GLib`.MainContext.get_thread_default], if the thread-default context is the global-default context, this will return that [struct`GLib`.MainContext] (with a ref added to it) rather than returning None.

New in version 2.32.

acquire()[source]¶

Returns:: True if the operation succeeded, and this thread is now the owner of self.
Return type:: bool

Tries to become the owner of the specified context. If some other thread is the owner of the context, returns False immediately. Ownership is properly recursive: the owner can require ownership again and will release ownership when [method`GLib`.MainContext.release] is called as many times as [method`GLib`.MainContext.acquire].

You must be the owner of a context before you can call [method`GLib`.MainContext.prepare], [method`GLib`.MainContext.query], [method`GLib`.MainContext.check], [method`GLib`.MainContext.dispatch], [method`GLib`.MainContext.release].

Since 2.76 self can be None to use the global-default main context.

add_poll(fd, priority)[source]¶

Parameters:

fd (GLib.PollFD) – a GLib.PollFD structure holding information about a file descriptor to watch.
priority (int) – the priority for this file descriptor which should be the same as the priority used for [method`GLib`.Source.attach] to ensure that the file descriptor is polled whenever the results may be needed.

Adds a file descriptor to the set of file descriptors polled for this context. This will very seldom be used directly. Instead a typical event source will use g_source_add_unix_fd instead.

check(max_priority, fds)[source]¶

Parameters:

max_priority (int) – the maximum numerical priority of sources to check
fds ([GLib.PollFD]) – array of GLib.PollFD's that was passed to the last call to [method`GLib`.MainContext.query]

Returns:

True if some sources are ready to be dispatched.

Return type:

bool

Passes the results of polling back to the main loop. You should be careful to pass fds and its length n_fds as received from [method`GLib`.MainContext.query], as this functions relies on assumptions on how fds is filled.

You must have successfully acquired the context with [method`GLib`.MainContext.acquire] before you may call this function.

Since 2.76 self can be None to use the global-default main context.

dispatch()[source]¶

Dispatches all pending sources.

You must have successfully acquired the context with [method`GLib`.MainContext.acquire] before you may call this function.

Since 2.76 self can be None to use the global-default main context.

find_source_by_funcs_user_data(funcs, user_data)[source]¶

Parameters:

funcs (GLib.SourceFuncs) – the source_funcs passed to [ctor`GLib`.Source.new].
user_data (object or None) – the user data from the callback.

Returns:

the source, if one was found, otherwise None

Return type:

GLib.Source

Finds a source with the given source functions and user data. If multiple sources exist with the same source function and user data, the first one found will be returned.

find_source_by_id(source_id)[source]¶

Parameters:: source_id (int) – the source ID, as returned by [method`GLib`.Source.get_id].
Returns:: the GLib.Source
Return type:: GLib.Source

Finds a GLib.Source given a pair of context and ID.

It is a programmer error to attempt to look up a non-existent source.

More specifically: source IDs can be reissued after a source has been destroyed and therefore it is never valid to use this function with a source ID which may have already been removed. An example is when scheduling an idle to run in another thread with [func`GLib`.idle_add]: the idle may already have run and been removed by the time this function is called on its (now invalid) source ID. This source ID may have been reissued, leading to the operation being performed against the wrong source.

find_source_by_user_data(user_data)[source]¶

Parameters:: user_data (object or None) – the user_data for the callback.
Returns:: the source, if one was found, otherwise None
Return type:: GLib.Source

Finds a source with the given user data for the callback. If multiple sources exist with the same user data, the first one found will be returned.

invoke_full(priority, function, *data)[source]¶

Parameters:

priority (int) – the priority at which to run function
function (GLib.SourceFunc) – function to call
data (object or None) – data to pass to function

Invokes a function in such a way that self is owned during the invocation of function.

This function is the same as [method`GLib`.MainContext.invoke] except that it lets you specify the priority in case function ends up being scheduled as an idle and also lets you give a GLib.DestroyNotify for data.

notify should not assume that it is called from any particular thread or with any particular context acquired.

New in version 2.28.

is_owner()[source]¶

Returns:: True if current thread is owner of self.
Return type:: bool

Determines whether this thread holds the (recursive) ownership of this [struct`GLib`.MainContext]. This is useful to know before waiting on another thread that may be blocking to get ownership of self.

New in version 2.10.

iteration(may_block)[source]¶

Parameters:: may_block (bool) – whether the call may block.
Returns:: True if events were dispatched.
Return type:: bool

Runs a single iteration for the given main loop. This involves checking to see if any event sources are ready to be processed, then if no events sources are ready and may_block is True, waiting for a source to become ready, then dispatching the highest priority events sources that are ready. Otherwise, if may_block is False sources are not waited to become ready, only those highest priority events sources will be dispatched (if any), that are ready at this given moment without further waiting.

Note that even when may_block is True, it is still possible for [method`GLib`.MainContext.iteration] to return False, since the wait may be interrupted for other reasons than an event source becoming ready.

pending()[source]¶

Returns:: True if events are pending.
Return type:: bool

Checks if any sources have pending events for the given context.

pop_thread_default()[source]¶: Pops self off the thread-default context stack (verifying that it was on the top of the stack).

New in version 2.22.

prepare()[source]¶

Returns:

True if some source is ready to be dispatched prior to polling.

priority:: location to store priority of highest priority source already ready.

Return type:

(bool, priority: int)

Prepares to poll sources within a main loop. The resulting information for polling is determined by calling [method`GLib`.MainContext.query].

You must have successfully acquired the context with [method`GLib`.MainContext.acquire] before you may call this function.

push_thread_default()[source]¶

Acquires self and sets it as the thread-default context for the current thread. This will cause certain asynchronous operations (such as most ‘gio [gio]’-based I/O) which are started in this thread to run under self and deliver their results to its main loop, rather than running under the global default main context in the main thread. Note that calling this function changes the context returned by [func`GLib`.MainContext.get_thread_default], not the one returned by [func`GLib`.MainContext.default], so it does not affect the context used by functions like [func`GLib`.idle_add].

Normally you would call this function shortly after creating a new thread, passing it a [struct`GLib`.MainContext] which will be run by a [struct`GLib`.MainLoop] in that thread, to set a new default context for all async operations in that thread. In this case you may not need to ever call [method`GLib`.MainContext.pop_thread_default], assuming you want the new [struct`GLib`.MainContext] to be the default for the whole lifecycle of the thread.

If you don’t have control over how the new thread was created (e.g. in the new thread isn’t newly created, or if the thread life cycle is managed by a GLib.ThreadPool), it is always suggested to wrap the logic that needs to use the new [struct`GLib`.MainContext] inside a [method`GLib`.MainContext.push_thread_default] / [method`GLib`.MainContext.pop_thread_default] pair, otherwise threads that are re-used will end up never explicitly releasing the [struct`GLib`.MainContext] reference they hold.

In some cases you may want to schedule a single operation in a non-default context, or temporarily use a non-default context in the main thread. In that case, you can wrap the call to the asynchronous operation inside a [method`GLib`.MainContext.push_thread_default] / [method`GLib`.MainContext.pop_thread_default] pair, but it is up to you to ensure that no other asynchronous operations accidentally get started while the non-default context is active.

Beware that libraries that predate this function may not correctly handle being used from a thread with a thread-default context. Eg, see g_file_supports_thread_contexts().

New in version 2.22.

pusher_new()¶

Returns:: a #GMainContextPusher
Return type:: object

Push self as the new thread-default main context for the current thread, using [method`GLib`.MainContext.push_thread_default], and return a new [alias`GLib`.MainContextPusher]. Pop with g_main_context_pusher_free(). Using [method`GLib`.MainContext.pop_thread_default] on self while a [alias`GLib`.MainContextPusher] exists for it can lead to undefined behaviour.

Using two [alias`GLib`.MainContextPusher]s in the same scope is not allowed, as it leads to an undefined pop order.

This is intended to be used with g_autoptr(). Note that g_autoptr() is only available when using GCC or clang, so the following example will only work with those compilers:

typedef struct
{
  ...
  GMainContext *context;
  ...
} MyObject;

static void
my_object_do_stuff (MyObject *self)
{
  g_autoptr(GMainContextPusher) pusher = g_main_context_pusher_new (self->context);

  // Code with main context as the thread default here

  if (cond)
    // No need to pop
    return;

  // Optionally early pop
  g_clear_pointer (&pusher, g_main_context_pusher_free);

  // Code with main context no longer the thread default here
}

New in version 2.64.

query(max_priority)[source]¶

Parameters:

max_priority (int) – maximum priority source to check

Returns:

the number of records actually stored in fds, or, if more than n_fds records need to be stored, the number of records that need to be stored.

timeout_:: location to store timeout to be used in polling
fds:: location to store GLib.PollFD records that need to be polled.

Return type:

(int, timeout_: int, fds: [GLib.PollFD])

Determines information necessary to poll this main loop. You should be careful to pass the resulting fds array and its length n_fds as is when calling [method`GLib`.MainContext.check], as this function relies on assumptions made when the array is filled.

You must have successfully acquired the context with [method`GLib`.MainContext.acquire] before you may call this function.

ref()[source]¶

Returns:: the self that was passed in (since 2.6)
Return type:: GLib.MainContext

Increases the reference count on a [struct`GLib`.MainContext] object by one.

release()[source]¶

Releases ownership of a context previously acquired by this thread with [method`GLib`.MainContext.acquire]. If the context was acquired multiple times, the ownership will be released only when [method`GLib`.MainContext.release] is called as many times as it was acquired.

You must have successfully acquired the context with [method`GLib`.MainContext.acquire] before you may call this function.

remove_poll(fd)[source]¶

Parameters:: fd (GLib.PollFD) – a GLib.PollFD descriptor previously added with [method`GLib`.MainContext.add_poll]

Removes file descriptor from the set of file descriptors to be polled for a particular context.

unref()[source]¶: Decreases the reference count on a [struct`GLib`.MainContext] object by one. If the result is zero, free the context and free all associated memory.

wait(cond, mutex)[source]¶

Parameters:

cond (GLib.Cond) – a condition variable
mutex (GLib.Mutex) – a mutex, currently held

Returns:

True if the operation succeeded, and this thread is now the owner of self.

Return type:

bool

Tries to become the owner of the specified context, as with [method`GLib`.MainContext.acquire]. But if another thread is the owner, atomically drop mutex and wait on cond until that owner releases ownership or until cond is signaled, then try again (once) to become the owner.

Deprecated since version 2.58: Use [method`GLib`.MainContext.is_owner] and separate locking instead.

wakeup()[source]¶

If self is currently blocking in [method`GLib`.MainContext.iteration] waiting for a source to become ready, cause it to stop blocking and return. Otherwise, cause the next invocation of [method`GLib`.MainContext.iteration] to return without blocking.

This API is useful for low-level control over [struct`GLib`.MainContext]; for example, integrating it with main loop implementations such as [struct`GLib`.MainLoop].

Another related use for this function is when implementing a main loop with a termination condition, computed from multiple threads:

#define NUM_TASKS 10
static gint tasks_remaining = NUM_TASKS;  // (atomic)
...

while (g_atomic_int_get (&tasks_remaining) != 0)
  g_main_context_iteration (NULL, TRUE);

Then in a thread:

perform_work();

if (g_atomic_int_dec_and_test (&tasks_remaining))
  g_main_context_wakeup (NULL);