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Functions
Description
Sometimes you wish to asynchronously fork out the execution of work and continue working in your own thread. If that will happen often, the overhead of starting and destroying a thread each time might be too high. In such cases reusing already started threads seems like a good idea. And it indeed is, but implementing this can be tedious and error-prone.
Therefore GLib provides thread pools for your convenience. An added advantage is, that the threads can be shared between the different subsystems of your program, when they are using GLib.
To create a new thread pool, you use g_thread_pool_new()
.
It is destroyed by g_thread_pool_free()
.
If you want to execute a certain task within a thread pool,
you call g_thread_pool_push()
.
To get the current number of running threads you call
g_thread_pool_get_num_threads()
. To get the number of still
unprocessed tasks you call g_thread_pool_unprocessed()
. To control
the maximal number of threads for a thread pool, you use
g_thread_pool_get_max_threads()
and g_thread_pool_set_max_threads()
.
Finally you can control the number of unused threads, that are kept
alive by GLib for future use. The current number can be fetched with
g_thread_pool_get_num_unused_threads()
. The maximal number can be
controlled by g_thread_pool_get_max_unused_threads()
and
g_thread_pool_set_max_unused_threads()
. All currently unused threads
can be stopped by calling g_thread_pool_stop_unused_threads()
.
Functions
g_thread_pool_new ()
GThreadPool * g_thread_pool_new (GFunc func
,gpointer user_data
,gint max_threads
,gboolean exclusive
,GError **error
);
This function creates a new thread pool.
Whenever you call g_thread_pool_push()
, either a new thread is
created or an unused one is reused. At most max_threads
threads
are running concurrently for this thread pool. max_threads
= -1
allows unlimited threads to be created for this thread pool. The
newly created or reused thread now executes the function func
with the two arguments. The first one is the parameter to
g_thread_pool_push()
and the second one is user_data
.
The parameter exclusive
determines whether the thread pool owns
all threads exclusive or shares them with other thread pools.
If exclusive
is TRUE
, max_threads
threads are started
immediately and they will run exclusively for this thread pool
until it is destroyed by g_thread_pool_free()
. If exclusive
is
FALSE
, threads are created when needed and shared between all
non-exclusive thread pools. This implies that max_threads
may
not be -1 for exclusive thread pools. Besides, exclusive thread
pools are not affected by g_thread_pool_set_max_idle_time()
since their threads are never considered idle and returned to the
global pool.
error
can be NULL
to ignore errors, or non-NULL
to report
errors. An error can only occur when exclusive
is set to TRUE
and not all max_threads
threads could be created.
See GThreadError for possible errors that may occur.
Note, even in case of error a valid GThreadPool is returned.
Parameters
func |
a function to execute in the threads of the new thread pool |
|
user_data |
user data that is handed over to |
|
max_threads |
the maximal number of threads to execute concurrently in the new thread pool, -1 means no limit |
|
exclusive |
should this thread pool be exclusive? |
|
error |
return location for error, or |
g_thread_pool_push ()
gboolean g_thread_pool_push (GThreadPool *pool
,gpointer data
,GError **error
);
Inserts data
into the list of tasks to be executed by pool
.
When the number of currently running threads is lower than the
maximal allowed number of threads, a new thread is started (or
reused) with the properties given to g_thread_pool_new()
.
Otherwise, data
stays in the queue until a thread in this pool
finishes its previous task and processes data
.
error
can be NULL
to ignore errors, or non-NULL
to report
errors. An error can only occur when a new thread couldn't be
created. In that case data
is simply appended to the queue of
work to do.
Before version 2.32, this function did not return a success status.
g_thread_pool_set_max_threads ()
gboolean g_thread_pool_set_max_threads (GThreadPool *pool
,gint max_threads
,GError **error
);
Sets the maximal allowed number of threads for pool
.
A value of -1 means that the maximal number of threads
is unlimited. If pool
is an exclusive thread pool, setting
the maximal number of threads to -1 is not allowed.
Setting max_threads
to 0 means stopping all work for pool
.
It is effectively frozen until max_threads
is set to a non-zero
value again.
A thread is never terminated while calling func
, as supplied by
g_thread_pool_new()
. Instead the maximal number of threads only
has effect for the allocation of new threads in g_thread_pool_push()
.
A new thread is allocated, whenever the number of currently
running threads in pool
is smaller than the maximal number.
error
can be NULL
to ignore errors, or non-NULL
to report
errors. An error can only occur when a new thread couldn't be
created.
Before version 2.32, this function did not return a success status.
Parameters
pool |
||
max_threads |
a new maximal number of threads for |
|
error |
return location for error, or |
g_thread_pool_get_max_threads ()
gint
g_thread_pool_get_max_threads (GThreadPool *pool
);
Returns the maximal number of threads for pool
.
g_thread_pool_get_num_threads ()
guint
g_thread_pool_get_num_threads (GThreadPool *pool
);
Returns the number of threads currently running in pool
.
g_thread_pool_unprocessed ()
guint
g_thread_pool_unprocessed (GThreadPool *pool
);
Returns the number of tasks still unprocessed in pool
.
g_thread_pool_free ()
void g_thread_pool_free (GThreadPool *pool
,gboolean immediate
,gboolean wait_
);
Frees all resources allocated for pool
.
If immediate
is TRUE
, no new task is processed for pool
.
Otherwise pool
is not freed before the last task is processed.
Note however, that no thread of this pool is interrupted while
processing a task. Instead at least all still running threads
can finish their tasks before the pool
is freed.
If wait_
is TRUE
, the functions does not return before all
tasks to be processed (dependent on immediate
, whether all
or only the currently running) are ready.
Otherwise the function returns immediately.
After calling this function pool
must not be used anymore.
g_thread_pool_set_max_unused_threads ()
void
g_thread_pool_set_max_unused_threads (gint max_threads
);
Sets the maximal number of unused threads to max_threads
.
If max_threads
is -1, no limit is imposed on the number
of unused threads.
The default value is 2.
g_thread_pool_get_max_unused_threads ()
gint
g_thread_pool_get_max_unused_threads (void
);
Returns the maximal allowed number of unused threads.
g_thread_pool_get_num_unused_threads ()
guint
g_thread_pool_get_num_unused_threads (void
);
Returns the number of currently unused threads.
g_thread_pool_stop_unused_threads ()
void
g_thread_pool_stop_unused_threads (void
);
Stops all currently unused threads. This does not change the
maximal number of unused threads. This function can be used to
regularly stop all unused threads e.g. from g_timeout_add()
.
g_thread_pool_set_sort_function ()
void g_thread_pool_set_sort_function (GThreadPool *pool
,GCompareDataFunc func
,gpointer user_data
);
Sets the function used to sort the list of tasks. This allows the
tasks to be processed by a priority determined by func
, and not
just in the order in which they were added to the pool.
Note, if the maximum number of threads is more than 1, the order that threads are executed cannot be guaranteed 100%. Threads are scheduled by the operating system and are executed at random. It cannot be assumed that threads are executed in the order they are created.
Parameters
pool |
||
func |
the GCompareDataFunc used to sort the list of tasks. This function is passed two tasks. It should return 0 if the order in which they are handled does not matter, a negative value if the first task should be processed before the second or a positive value if the second task should be processed first. |
|
user_data |
user data passed to |
Since: 2.10
g_thread_pool_set_max_idle_time ()
void
g_thread_pool_set_max_idle_time (guint interval
);
This function will set the maximum interval
that a thread
waiting in the pool for new tasks can be idle for before
being stopped. This function is similar to calling
g_thread_pool_stop_unused_threads()
on a regular timeout,
except this is done on a per thread basis.
By setting interval
to 0, idle threads will not be stopped.
The default value is 15000 (15 seconds).
Since: 2.10
g_thread_pool_get_max_idle_time ()
guint
g_thread_pool_get_max_idle_time (void
);
This function will return the maximum interval
that a
thread will wait in the thread pool for new tasks before
being stopped.
If this function returns 0, threads waiting in the thread pool for new work are not stopped.
Returns
the maximum interval
(milliseconds) to wait
for new tasks in the thread pool before stopping the
thread
Since: 2.10
g_thread_pool_move_to_front ()
gboolean g_thread_pool_move_to_front (GThreadPool *pool
,gpointer data
);
Moves the item to the front of the queue of unprocessed items, so that it will be processed next.
Since: 2.46
Types and Values
struct GThreadPool
struct GThreadPool { GFunc func; gpointer user_data; gboolean exclusive; };
The GThreadPool struct represents a thread pool. It has three public read-only members, but the underlying struct is bigger, so you must not copy this struct.