Class MainContext

java.lang.Object
org.javagi.base.ProxyInstance
org.gnome.glib.MainContext
All Implemented Interfaces:
Proxy
@Generated("org.javagi.JavaGI") public class MainContext extends ProxyInstance
The GMainContext struct is an opaque data type representing a set of sources to be handled in a main loop.

  • Constructor Details

    • MainContext

      public MainContext(MemorySegment address)
      Create a MainContext proxy instance for the provided memory address.
      Parameters:
      address - the memory address of the native object

    • MainContext

      public MainContext()
      Creates a new GLib.MainContext structure.

  • Method Details

    • getType

      public static @Nullable Type getType()
      Get the GType of the MainContext class.
      Returns:
      the GType

    • getMemoryLayout

      public static MemoryLayout getMemoryLayout()
      The memory layout of the native struct.
      Returns:
      the memory layout

    • withFlags

      public static MainContext withFlags(Set<MainContextFlags> flags)
      Creates a new GLib.MainContext structure.
      Parameters:
      flags - a bitwise-OR combination of flags that can only be set at creation time
      Returns:
      the new main context
      Since:
      2.72

    • withFlags

      public static MainContext withFlags(MainContextFlags... flags)
      Creates a new GLib.MainContext structure.
      Parameters:
      flags - a bitwise-OR combination of flags that can only be set at creation time
      Returns:
      the new main context
      Since:
      2.72

    • default_

      public static MainContext default_()

      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 getThreadDefault().

      Returns:
      the global-default main context.

    • getThreadDefault

      public static @Nullable MainContext getThreadDefault()

      Gets the thread-default main context 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 refThreadDefault() 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 NULL if you are running in the default thread.)

      If you need to hold a reference on the context, use refThreadDefault() instead.

      Returns:
      the thread-default main context, or NULL if the thread-default context is the global-default main context
      Since:
      2.22

    • pusherFree

      public static void pusherFree(MemorySegment pusher)

      Pop pusher’s main context as the thread default main context. See g_main_context_pusher_new() for details.

      This will pop the GLib.MainContext as the current thread-default main context, but will not call unref() on it.

      Parameters:
      pusher - a GMainContextPusher
      Since:
      2.64

    • refThreadDefault

      public static MainContext refThreadDefault()

      Gets a reference to the thread-default GLib.MainContext for this thread

      This is the same as getThreadDefault(), but it also adds a reference to the returned main context with ref(). In addition, unlike getThreadDefault(), 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 NULL.

      Returns:
      the thread-default main context
      Since:
      2.32

    • acquire

      public boolean acquire()

      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() is called as many times as acquire().

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

      Since 2.76 this MainContext can be NULL to use the global-default main context.

      Returns:
      true if this thread is now the owner of context, false otherwise

    • addPoll

      public void addPoll(PollFD fd, int priority)

      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.

      Parameters:
      fd - a GLib.PollFD structure holding information about a file descriptor to watch.
      priority - the priority for this file descriptor which should be the same as the priority used for Source.attach(MainContext) to ensure that the file descriptor is polled whenever the results may be needed.

    • dispatch

      public void dispatch()

      Dispatches all pending sources.

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

      Since 2.76 this MainContext can be NULL to use the global-default main context.

    • findSourceByFuncsUserData

      public @Nullable Source findSourceByFuncsUserData(SourceFuncs funcs, @Nullable MemorySegment userData)

      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.

      Parameters:
      funcs - the sourceFuncs passed to Source(SourceFuncs, int)
      userData - the user data from the callback
      Returns:
      the source, if one was found, otherwise NULL

    • findSourceById

      public Source findSourceById(int sourceId)

      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 GLib.idleAdd(int, SourceFunc): 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.

      Parameters:
      sourceId - the source ID, as returned by Source.getId()
      Returns:
      the source

    • findSourceByUserData

      public @Nullable Source findSourceByUserData(@Nullable MemorySegment userData)

      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.

      Parameters:
      userData - the user_data for the callback
      Returns:
      the source, if one was found, otherwise NULL

    • getPollFunc

      public @Nullable PollFunc getPollFunc()
      Gets the poll function set by setPollFunc(PollFunc).
      Returns:
      the poll function

    • invoke

      public void invoke(@Nullable SourceFunc function)

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

      If this MainContext is NULL then the global-default main context — as returned by default_() — is used.

      If this MainContext is owned by the current thread, function is called directly. Otherwise, if this MainContext is the thread-default main context of the current thread and acquire() succeeds, then function is called and release() is called afterwards.

      In any other case, an idle source is created to call function and that source is attached to this MainContext (presumably to be run in another thread). The idle source is attached with GLib.PRIORITY_DEFAULT priority. If you want a different priority, use invokeFull(int, SourceFunc).

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

      Parameters:
      function - function to call
      Since:
      2.28

    • invokeFull

      public void invokeFull(int priority, @Nullable SourceFunc function)

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

      This function is the same as invoke(SourceFunc) 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.

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

      Parameters:
      priority - the priority at which to run function
      function - function to call
      Since:
      2.28

    • isOwner

      public boolean isOwner()

      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 context.

      Returns:
      true if current thread is owner of context, false otherwise
      Since:
      2.10

    • iteration

      public boolean iteration(boolean mayBlock)

      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, this function does not wait for sources to become ready, and only the highest priority sources which are already ready (if any) will be dispatched.

      Note that even when mayBlock is true, it is still possible for iteration(boolean) to return false, since the wait may be interrupted for other reasons than an event source becoming ready.

      Parameters:
      mayBlock - whether the call may block
      Returns:
      true if events were dispatched, false otherwise

    • pending

      public boolean pending()
      Checks if any sources have pending events for the given context.
      Returns:
      true if events are pending, false otherwise

    • popThreadDefault

      public void popThreadDefault()
      Pops this MainContext off the thread-default context stack (verifying that it was on the top of the stack).
      Since:
      2.22

    • prepare

      public boolean prepare(@Nullable Out<Integer> priority)

      Prepares to poll sources within a main loop.

      The resulting information for polling is determined by calling MainContext.query.

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

      Parameters:
      priority - location to store priority of highest priority source already ready
      Returns:
      true if some source is ready to be dispatched prior to polling, false otherwise

    • pushThreadDefault

      public void pushThreadDefault()

      Acquires this MainContext and sets it as the thread-default context for the current thread. This will cause certain asynchronous operations (such as most Gio-based I/O) which are started in this thread to run under this MainContext 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 getThreadDefault(), not the one returned by default_(), so it does not affect the context used by functions like GLib.idleAdd(int, SourceFunc).

      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 popThreadDefault(), 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 GThreadPool), it is always suggested to wrap the logic that needs to use the new GLib.MainContext inside a pushThreadDefault() / popThreadDefault() 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 pushThreadDefault() / popThreadDefault() 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. For example, see g_file_supports_thread_contexts().

      Since:
      2.22

    • pusherNew

      public MemorySegment pusherNew()

      Push this MainContext as the new thread-default main context for the current thread, using pushThreadDefault(), and return a new GLib.MainContextPusher. Pop with g_main_context_pusher_free(). Using popThreadDefault() on this MainContext while a GLib.MainContextPusher exists for it can lead to undefined behaviour.

      Using two GLib.MainContextPushers 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
}
      Returns:
      a GMainContextPusher
      Since:
      2.64

    • ref

      public MainContext ref()
      Increases the reference count on a GLib.MainContext object by one.
      Returns:
      the this MainContext that was passed in (since 2.6)

    • release

      public void release()

      Releases ownership of a context previously acquired by this thread with acquire().

      If the context was acquired multiple times, the ownership will be released only when release() is called as many times as it was acquired.

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

    • removePoll

      public void removePoll(PollFD fd)
      Removes file descriptor from the set of file descriptors to be polled for a particular context.
      Parameters:
      fd - a GLib.PollFD descriptor previously added with addPoll(PollFD, int)

    • setPollFunc

      public void setPollFunc(@Nullable PollFunc func)

      Sets the function to use to handle polling of file descriptors.

      It will be used instead of the poll() system call (or GLib’s replacement function, which is used where poll() isn’t available).

      This function could possibly be used to integrate the GLib event loop with an external event loop.

      Parameters:
      func - the function to call to poll all file descriptors

    • unref

      public void unref()
      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_

      @Deprecated public boolean wait_(Cond cond, Mutex mutex)
      Deprecated.
      Use isOwner() and separate locking instead.

      Tries to become the owner of the specified context, and waits on cond if another thread is the owner.

      This is the same as 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.

      Parameters:
      cond - a condition variable
      mutex - a mutex, currently held
      Returns:
      true if this thread is now the owner of context, false otherwise

    • wakeup

      public void wakeup()

      Wake up this MainContext if it’s currently blocking in iteration(boolean), causing it to stop blocking.

      The this MainContext could be blocking waiting for a source to become ready. Otherwise, if this MainContext is not currently blocking, this function causes the next invocation of iteration(boolean) 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 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);