GLib.MainContext

Fields

None

Methods

class default ()
class get_thread_default ()
class new ()
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 (priority)
  push_thread_default ()
  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 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 context.
Return type:GLib.MainContext

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 GLib.MainContext.ref_thread_default() to get a GLib.MainContext to add their GLib.Sources 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 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 GLib.MainContext structure.

classmethod ref_thread_default()[source]
Returns:the thread-default GLib.MainContext. Unref with GLib.MainContext.unref() when you are done with it.
Return type:GLib.MainContext

Gets the thread-default GLib.MainContext for this thread, as with GLib.MainContext.get_thread_default(), but also adds a reference to it with GLib.MainContext.ref(). In addition, unlike GLib.MainContext.get_thread_default(), if the thread-default context is the global default context, this will return that 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 GLib.MainContext.release() is called as many times as GLib.MainContext.acquire().

You must be the owner of a context before you can call GLib.MainContext.prepare(), GLib.MainContext.query(), GLib.MainContext.check(), GLib.MainContext.dispatch().

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 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 GLib.Source.add_unix_fd() instead.

check(max_priority, fds)[source]
Parameters:
Returns:

True if some sources are ready to be dispatched.

Return type:

bool

Passes the results of polling back to the main loop.

You must have successfully acquired the context with GLib.MainContext.acquire() before you may call this function.

dispatch()[source]

Dispatches all pending sources.

You must have successfully acquired the context with GLib.MainContext.acquire() before you may call this function.

find_source_by_funcs_user_data(funcs, user_data)[source]
Parameters:
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 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 lookup 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 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 g_main_context_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 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 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(priority)[source]
Parameters:priority (int) – location to store priority of highest priority source already ready.
Returns:True if some source is ready to be dispatched prior to polling.
Return type:bool

Prepares to poll sources within a main loop. The resulting information for polling is determined by calling GLib.MainContext.query ().

You must have successfully acquired the context with 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 context in the main thread. Note that calling this function changes the context returned by GLib.MainContext.get_thread_default(), not the one returned by GLib.MainContext.default(), so it does not affect the context used by functions like GLib.idle_add().

Normally you would call this function shortly after creating a new thread, passing it a GLib.MainContext which will be run by a 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 GLib.MainContext.pop_thread_default(), assuming you want the new 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 GLib.MainContext inside a GLib.MainContext.push_thread_default() / GLib.MainContext.pop_thread_default() pair, otherwise threads that are re-used will end up never explicitly releasing the 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 GLib.MainContext.push_thread_default() / 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.

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 must have successfully acquired the context with 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 GLib.MainContext object by one.

release()[source]

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

remove_poll(fd)[source]
Parameters:fd (GLib.PollFD) – a GLib.PollFD descriptor previously added with 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 GLib.MainContext object by one. If the result is zero, free the context and free all associated memory.

wait(cond, mutex)[source]
Parameters:
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 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.

wakeup()[source]

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

This API is useful for low-level control over GLib.MainContext; for example, integrating it with main loop implementations such as 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 volatile gint tasks_remaining = NUM_TASKS;
...

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);