### Struct

# GLib MainContext

#### Description

    struct GMainContext {
      /* No available fields */
    }

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

#### Constructors

###### g_main_context_new

Creates a new `GMainContext` structure.

###### g_main_context_new_with_flags

Creates a new `GMainContext` structure.

since: 2.72

#### Functions

###### g_main_context_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 g_main_context_get_thread_default().

###### g_main_context_get_thread_default

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 `g_main_context_ref_thread_default()` to get a `GMainContext` 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 `NULL` if you are running in the default thread.).

since: 2.22

###### g_main_context_ref_thread_default

Gets the thread-default `GMainContext` for this thread, as with g_main_context_get_thread_default(), but also adds a reference to it with g_main_context_ref(). In addition, unlike g_main_context_get_thread_default(), if the thread-default context is the global-default context, this will return that `GMainContext` (with a ref added to it) rather than returning `NULL`.

since: 2.32

#### Instance methods

###### g_main_context_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 `g_main_context_release()` is called as many times as g_main_context_acquire().

###### g_main_context_add_poll

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.

###### g_main_context_check

Passes the results of polling back to the main loop. You should be careful to pass `fds` and its length `n_fds` as received from g_main_context_query(), as this functions relies on assumptions on how `fds` is filled.

###### g_main_context_dispatch

Dispatches all pending sources.

###### g_main_context_find_source_by_funcs_user_data

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.

###### g_main_context_find_source_by_id

Finds a `GSource` given a pair of context and ID.

###### g_main_context_find_source_by_user_data

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.

###### g_main_context_get_poll_func

Gets the poll function set by g_main_context_set_poll_func().

###### g_main_context_invoke

Invokes a function in such a way that `context` is owned during the invocation of `function`.

since: 2.28

###### g_main_context_invoke_full

Invokes a function in such a way that `context` is owned during the invocation of `function`.

since: 2.28

###### g_main_context_is_owner

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

since: 2.10

###### g_main_context_iteration

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.

###### g_main_context_pending

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

###### g_main_context_pop_thread_default

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

since: 2.22

###### g_main_context_prepare

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

###### g_main_context_push_thread_default

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 main context in the main thread. Note that calling this function changes the context returned by g_main_context_get_thread_default(), not the one returned by g_main_context_default(), so it does not affect the context used by functions like g_idle_add().

since: 2.22

###### g_main_context_query

Determines information necessary to poll this main loop. You should be careful to pass the resulting `fds` array and its length `n_fds` as is when calling g_main_context_check(), as this function relies on assumptions made when the array is filled.

###### g_main_context_ref

Increases the reference count on a `GMainContext` object by one.

###### g_main_context_release

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

###### g_main_context_remove_poll

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

###### g_main_context_set_poll_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).

###### g_main_context_unref

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

###### g_main_context_wait

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

deprecated: 2.58

###### g_main_context_wakeup

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