Struct MainContext

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pub struct MainContext { /* private fields */ }

Expand description

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

GLib type: Shared boxed type with reference counted clone semantics.

Implementations§

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impl MainContext

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pub fn as_ptr(&self) -> *mut GMainContext

Return the inner pointer to the underlying C value.

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pub unsafe fn from_glib_ptr_borrow(ptr: &*mut GMainContext) -> &Self

Borrows the underlying C value.

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impl MainContext

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pub fn new() -> MainContext

Creates a new MainContext structure.

§Returns

the new #GMainContext

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pub fn with_flags(flags: MainContextFlags) -> MainContext

Available on crate feature v2_72 only.

Creates a new MainContext structure.

§`flags`

a bitwise-OR combination of #GMainContextFlags flags that can only be set at creation time.

§Returns

the new #GMainContext

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pub fn dispatch(&self)

Dispatches all pending sources.

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

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

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pub fn is_owner(&self) -> bool

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

§Returns

true if current thread is owner of @self.

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pub fn iteration(&self, may_block: bool) -> 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 iteration() to return false, since the wait may be interrupted for other reasons than an event source becoming ready.

§`may_block`

whether the call may block.

§Returns

true if events were dispatched.

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pub fn pending(&self) -> bool

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

§Returns

true if events are pending.

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pub fn wakeup(&self)

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

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

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

⚠️ The following code is in C ⚠️

  #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:

⚠️ The following code is in C ⚠️

  perform_work();

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

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pub fn default() -> 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 thread_default().

§Returns

the global-default main context.

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pub fn thread_default() -> Option<MainContext>

Gets the thread-default #GMainContext 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 ref_thread_default() to get a MainContext to add their 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 ref_thread_default() instead.

§Returns

the thread-default #GMainContext, or None if the thread-default context is the global-default main context.

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pub fn ref_thread_default() -> MainContext

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

§Returns

the thread-default #GMainContext. Unref with GLib::MainContext::unref() when you are done with it.

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impl MainContext

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pub fn prepare(&self) -> (bool, i32)

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 acquire() before you may call this function.

§Returns

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

§`priority`

location to store priority of highest priority source already ready.

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pub fn find_source_by_id(&self, source_id: &SourceId) -> Option<Source>

Finds a #GSource 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 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.

§`source_id`

the source ID, as returned by GLib::Source::get_id().

§Returns

the #GSource

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pub fn invoke<F>(&self, func: F)
where F: FnOnce() + Send + 'static,

Invokes func on the main context.

If the current thread is the owner of the main context or the main context currently has no owner then func will be called directly from inside this function. If this behaviour is not desired and func should always be called asynchronously then use MainContext::spawn glib::idle_add instead. Invokes a function in such a way that @self is owned during the invocation of @function.

If @self is None then the global-default main context — as returned by default() — is used.

If @self is owned by the current thread, @function is called directly. Otherwise, if @self is the thread-default main context of the current thread and acquire() succeeds, then @function is called and [release()][Self::release()] is called afterwards.

In any other case, an idle source is created to call @function and that source is attached to @self (presumably to be run in another thread). The idle source is attached with GLib::PRIORITY_DEFAULT priority. If you want a different priority, use [invoke_full()][Self::invoke_full()].

Note that, as with normal idle functions, @function should probably return false. If it returns true, it will be continuously run in a loop (and may prevent this call from returning).

§`function`

function to call

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pub fn invoke_with_priority<F>(&self, priority: Priority, func: F)
where F: FnOnce() + Send + 'static,

Invokes func on the main context with the given priority.

If the current thread is the owner of the main context or the main context currently has no owner then func will be called directly from inside this function. If this behaviour is not desired and func should always be called asynchronously then use MainContext::spawn glib::idle_add instead.

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pub fn invoke_local<F>(&self, func: F)
where F: FnOnce() + 'static,

Invokes func on the main context.

Different to invoke(), this does not require func to be Send but can only be called from the thread that owns the main context.

This function panics if called from a different thread than the one that owns the main context.

Note that this effectively means that func is called directly from inside this function or otherwise panics immediately. If this behaviour is not desired and func should always be called asynchronously then use MainContext::spawn_local glib::idle_add_local instead.

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pub fn invoke_local_with_priority<F>(&self, _priority: Priority, func: F)
where F: FnOnce() + 'static,

Invokes func on the main context with the given priority.

Different to invoke_with_priority(), this does not require func to be Send but can only be called from the thread that owns the main context.

This function panics if called from a different thread than the one that owns the main context.

Note that this effectively means that func is called directly from inside this function or otherwise panics immediately. If this behaviour is not desired and func should always be called asynchronously then use MainContext::spawn_local glib::idle_add_local instead.

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pub fn with_thread_default<R, F: FnOnce() -> R + Sized>( &self, func: F, ) -> Result<R, BoolError>

Call closure with the main context configured as the thread default one.

The thread default main context is changed in a panic-safe manner before calling func and released again afterwards regardless of whether closure panicked or not.

This will fail if the main context is owned already by another thread.

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pub fn acquire(&self) -> Result<MainContextAcquireGuard<'_>, BoolError>

Acquire ownership of the main context.

Ownership will automatically be released again once the returned acquire guard is dropped.

This will fail if the main context is owned already by another thread. 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 [release()][Self::release()] is called as many times as acquire().

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

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

§Returns

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

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impl MainContext

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pub fn spawn<R: Send + 'static, F: Future<Output = R> + Send + 'static>( &self, f: F, ) -> JoinHandle<R> ⓘ

Spawn a new infallible Future on the main context.

This can be called from any thread and will execute the future from the thread where main context is running, e.g. via a MainLoop.

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pub fn spawn_local<R: 'static, F: Future<Output = R> + 'static>( &self, f: F, ) -> JoinHandle<R> ⓘ

Spawn a new infallible Future on the main context.

The given Future does not have to be Send.

This can be called only from the thread where the main context is running, e.g. from any other Future that is executed on this main context, or after calling with_thread_default or acquire on the main context.

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pub fn spawn_with_priority<R: Send + 'static, F: Future<Output = R> + Send + 'static>( &self, priority: Priority, f: F, ) -> JoinHandle<R> ⓘ

Spawn a new infallible Future on the main context, with a non-default priority.

This can be called from any thread and will execute the future from the thread where main context is running, e.g. via a MainLoop.

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pub fn spawn_local_with_priority<R: 'static, F: Future<Output = R> + 'static>( &self, priority: Priority, f: F, ) -> JoinHandle<R> ⓘ

Spawn a new infallible Future on the main context, with a non-default priority.

The given Future does not have to be Send.

This can be called only from the thread where the main context is running, e.g. from any other Future that is executed on this main context, or after calling with_thread_default or acquire on the main context.

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