GI.GLib.Structs.MainContext

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

Exported types

newtype MainContext

Memory-managed wrapper type.

Constructors

MainContext (ManagedPtr MainContext)

Instances

BoxedObject MainContext

Defined in GI.GLib.Structs.MainContext

Methods

boxedType :: MainContext -> IO GType

noMainContext :: Maybe MainContext

A convenience alias for Nothing :: Maybe MainContext.

Methods

acquire

mainContextAcquire

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m Bool

Returns: True if the operation succeeded, and this thread is now the owner of context.

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 mainContextRelease is called as many times as mainContextAcquire.

You must be the owner of a context before you can call mainContextPrepare, mainContextQuery, mainContextCheck, mainContextDispatch.

addPoll

mainContextAddPoll

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext (or Nothing for the default context)

-> PollFD

fd: a PollFD structure holding information about a file descriptor to watch.

-> Int32

priority: the priority for this file descriptor which should be the same as the priority used for sourceAttach to ensure that the file descriptor is polled whenever the results may be needed.

-> m ()

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 sourceAddUnixFd instead.

check

mainContextCheck

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> Int32

maxPriority: the maximum numerical priority of sources to check

-> [PollFD]

fds: array of 'GI.GLib.Structs.PollFD.PollFD'\'s that was passed to the last call to mainContextQuery

-> m Bool

Returns: True if some sources are ready to be dispatched.

Passes the results of polling back to the main loop.

You must have successfully acquired the context with mainContextAcquire before you may call this function.

default

mainContextDefault

Arguments

:: (HasCallStack, MonadIO m)

=> m MainContext

Returns: the global default main context.

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 mainContextGetThreadDefault.

dispatch

mainContextDispatch

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m ()

Dispatches all pending sources.

You must have successfully acquired the context with mainContextAcquire before you may call this function.

findSourceByFuncsUserData

mainContextFindSourceByFuncsUserData

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext (if Nothing, the default context will be used).

-> SourceFuncs

funcs: the sourceFuncs passed to sourceNew.

-> Ptr ()

userData: the user data from the callback.

-> m Source

Returns: the source, if one was found, otherwise Nothing

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.

findSourceById

mainContextFindSourceById

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext (if Nothing, the default context will be used)

-> Word32

sourceId: the source ID, as returned by sourceGetId.

-> m Source

Returns: the Source

Finds a 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 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.

findSourceByUserData

mainContextFindSourceByUserData

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> Ptr ()

userData: the user_data for the callback.

-> m Source

Returns: the source, if one was found, otherwise Nothing

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.

getThreadDefault

mainContextGetThreadDefault

Arguments

:: (HasCallStack, MonadIO m)

=> m MainContext

Returns: the thread-default MainContext, or Nothing if the thread-default context is the global default context.

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 mainContextRefThreadDefault 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 Nothing if you are running in the default thread.)

If you need to hold a reference on the context, use mainContextRefThreadDefault instead.

Since: 2.22

invokeFull

mainContextInvokeFull

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext, or Nothing

-> Int32

priority: the priority at which to run function

-> SourceFunc

function: function to call

-> m ()

Invokes a function in such a way that context 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 DestroyNotify for data.

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

Since: 2.28

isOwner

mainContextIsOwner

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m Bool

Returns: True if current thread is owner of context.

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 context.

Since: 2.10

iteration

mainContextIteration

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext (if Nothing, the default context will be used)

-> Bool

mayBlock: whether the call may block.

-> m Bool

Returns: True if events were dispatched.

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 mayBlock is True, waiting for a source to become ready, then dispatching the highest priority events sources that are ready. Otherwise, if mayBlock 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 mayBlock is True, it is still possible for mainContextIteration to return False, since the wait may be interrupted for other reasons than an event source becoming ready.

new

mainContextNew

Arguments

:: (HasCallStack, MonadIO m)

=> m MainContext

Returns: the new MainContext

Creates a new MainContext structure.

pending

mainContextPending

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext (if Nothing, the default context will be used)

-> m Bool

Returns: True if events are pending.

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

popThreadDefault

mainContextPopThreadDefault

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext object, or Nothing

-> m ()

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

Since: 2.22

prepare

mainContextPrepare

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> Int32

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

-> m Bool

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

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 mainContextAcquire before you may call this function.

pushThreadDefault

mainContextPushThreadDefault

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext, or Nothing for the global default context

-> m ()

Acquires context 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 context 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 mainContextGetThreadDefault, not the one returned by mainContextDefault, 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 mainContextPopThreadDefault, 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 ThreadPool), it is always suggested to wrap the logic that needs to use the new MainContext inside a mainContextPushThreadDefault / mainContextPopThreadDefault 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 mainContextPushThreadDefault / mainContextPopThreadDefault 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().

Since: 2.22

query

mainContextQuery

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> Int32

maxPriority: maximum priority source to check

-> [PollFD]

fds: location to store PollFD records that need to be polled.

-> m (Int32, Int32, [PollFD])

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

Determines information necessary to poll this main loop.

You must have successfully acquired the context with mainContextAcquire before you may call this function.

ref

mainContextRef

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m MainContext

Returns: the context that was passed in (since 2.6)

Increases the reference count on a MainContext object by one.

refThreadDefault

mainContextRefThreadDefault

Arguments

:: (HasCallStack, MonadIO m)

=> m MainContext

Returns: the thread-default MainContext. Unref with mainContextUnref when you are done with it.

Gets the thread-default MainContext for this thread, as with mainContextGetThreadDefault, but also adds a reference to it with mainContextRef. In addition, unlike mainContextGetThreadDefault, if the thread-default context is the global default context, this will return that MainContext (with a ref added to it) rather than returning Nothing.

Since: 2.32

release

mainContextRelease

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m ()

Releases ownership of a context previously acquired by this thread with mainContextAcquire. If the context was acquired multiple times, the ownership will be released only when mainContextRelease is called as many times as it was acquired.

removePoll

mainContextRemovePoll

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> PollFD

fd: a PollFD descriptor previously added with mainContextAddPoll

-> m ()

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

unref

mainContextUnref

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m ()

Decreases the reference count on a MainContext object by one. If the result is zero, free the context and free all associated memory.

wait

mainContextWait

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> Cond

cond: a condition variable

-> Mutex

mutex: a mutex, currently held

-> m Bool

Returns: True if the operation succeeded, and this thread is now the owner of context.

Deprecated: (Since version 2.58)Use mainContextIsOwner and separate locking instead.

Tries to become the owner of the specified context, as with mainContextAcquire. 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

mainContextWakeup

Arguments

:: (HasCallStack, MonadIO m)

=> MainContext

context: a MainContext

-> m ()

If context is currently blocking in mainContextIteration waiting for a source to become ready, cause it to stop blocking and return. Otherwise, cause the next invocation of mainContextIteration 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:

C code

 #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:

C code

 perform_work();

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