Struct glib::MainContext

pub struct MainContext(_);

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

Implementations

impl MainContext

pub fn new() -> MainContext

Creates a new MainContext structure.

Returns

the new MainContext

pub fn dispatch(&self)

Dispatches all pending sources.

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

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.

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.

pub fn pending(&self) -> bool

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

Returns

true if events are pending.

pub fn pop_thread_default(&self)

Pops self off the thread-default context stack (verifying that it was on the top of the stack).

pub fn push_thread_default(&self)

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 thread_default(), not the one returned by default(), so it does not affect the context used by functions like g_idle_add().

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

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);

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.

pub fn thread_default() -> Option<MainContext>

Gets the thread-default 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 ref_thread_default() to get a MainContext to add their GSources 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 MainContext, or None if the thread-default context is the global default context.

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 g_main_context_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 MainContext. Unref with g_main_context_unref() when you are done with it.

impl MainContext

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

Prepares to poll sources within a main loop. The resulting information for polling is determined by calling g_main_context_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.

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

Finds a 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 g_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 g_source_get_id().

Returns

the Source

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

Invokes func on the main context. 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 G_PRIORITY_DEFAULT priority. If you want a different priority, use g_main_context_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

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.

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.

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.

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

Calls closure with context configured as the thread default one.

Thread default context is changed in panic-safe manner by calling push_thread_default before calling closure and pop_thread_default afterwards regardless of whether closure panicked or not.

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

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(), g_main_context_query(), g_main_context_check(), dispatch().

Returns

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

impl MainContext

pub fn channel<T>(priority: Priority) -> (Sender<T>, Receiver<T>)

Creates a channel for a main context.

The Receiver has to be attached to a main context at a later time, together with a closure that will be called for every item sent to a Sender.

The Sender can be cloned and both the Sender and Receiver can be sent to different threads as long as the item type implements the Send trait.

When the last Sender is dropped the channel is removed from the main context. If the Receiver is dropped and not attached to a main context all sending to the Sender will fail.

The returned Sender behaves the same as std::sync::mpsc::Sender.

pub fn sync_channel<T>(
    priority: Priority,
    bound: usize
) -> (SyncSender<T>, Receiver<T>)

Creates a synchronous channel for a main context with a given bound on the capacity of the channel.

The Receiver has to be attached to a main context at a later time, together with a closure that will be called for every item sent to a SyncSender.

The SyncSender can be cloned and both the SyncSender and Receiver can be sent to different threads as long as the item type implements the Send trait.

When the last SyncSender is dropped the channel is removed from the main context. If the Receiver is dropped and not attached to a main context all sending to the SyncSender will fail.

The returned SyncSender behaves the same as std::sync::mpsc::SyncSender.

impl MainContext

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

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.

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

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 push_thread_default or acquire on the main context.

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

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.

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

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 push_thread_default or acquire on the main context.

pub fn block_on<F: Future>(&self, f: F) -> F::Output

Runs a new, infallible Future on the main context and block until it finished, returning the result of the Future.

The given Future does not have to be Send or 'static.

This must only be called if no MainLoop or anything else is running on this specific main context.

Trait Implementations

impl Clone for MainContext

fn clone(&self) -> MainContext

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MainContext

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for MainContext

fn default() -> Self

Returns the “default value” for a type.

impl Hash for MainContext

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl LocalSpawn for MainContext

fn spawn_local_obj(
    &self,
    f: LocalFutureObj<'static, ()>
) -> Result<(), SpawnError>

Spawns a future that will be run to completion.

fn status_local(&self) -> Result<(), SpawnError>

Determines whether the executor is able to spawn new tasks.

impl Ord for MainContext

fn cmp(&self, other: &MainContext) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl PartialEq<MainContext> for MainContext

fn eq(&self, other: &MainContext) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &MainContext) -> bool

This method tests for !=.

impl PartialOrd<MainContext> for MainContext

fn partial_cmp(&self, other: &MainContext) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Spawn for MainContext

fn spawn_obj(&self, f: FutureObj<'static, ()>) -> Result<(), SpawnError>

Spawns a future that will be run to completion.

fn status(&self) -> Result<(), SpawnError>

Determines whether the executor is able to spawn new tasks.

impl StaticType for MainContext

fn static_type() -> Type

Returns the type identifier of Self.

impl Eq for MainContext

impl Send for MainContext

impl StructuralEq for MainContext

impl StructuralPartialEq for MainContext

impl Sync for MainContext