Move GThread docs around

[platform/upstream/glib.git] / glib / gthread.c

/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * gthread.c: MT safety related functions
 * Copyright 1998 Sebastian Wilhelmi; University of Karlsruhe
 *                Owen Taylor
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/* Prelude {{{1 ----------------------------------------------------------- */

/*
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GLib at ftp://ftp.gtk.org/pub/gtk/.
 */

/*
 * MT safe
 */

/* implement gthread.h's inline functions */
#define G_IMPLEMENT_INLINES 1
#define __G_THREAD_C__

#include "config.h"

#include "deprecated/gthread.h"
#include "gthreadprivate.h"
#include "gslice.h"
#include "gmain.h"

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#ifndef G_OS_WIN32
#include <sys/time.h>
#include <time.h>
#else
#include <windows.h>
#endif /* G_OS_WIN32 */

#include <string.h>

#include "garray.h"
#include "gbitlock.h"
#include "gslist.h"
#include "gtestutils.h"
#include "gtimer.h"

/**
 * SECTION:threads
 * @title: Threads
 * @short_description: portable support for threads, mutexes, locks,
 *     conditions and thread private data
 * @see_also: #GThreadPool, #GAsyncQueue
 *
 * Threads act almost like processes, but unlike processes all threads
 * of one process share the same memory. This is good, as it provides
 * easy communication between the involved threads via this shared
 * memory, and it is bad, because strange things (so called
 * "Heisenbugs") might happen if the program is not carefully designed.
 * In particular, due to the concurrent nature of threads, no
 * assumptions on the order of execution of code running in different
 * threads can be made, unless order is explicitly forced by the
 * programmer through synchronization primitives.
 *
 * The aim of the thread-related functions in GLib is to provide a
 * portable means for writing multi-threaded software. There are
 * primitives for mutexes to protect the access to portions of memory
 * (#GMutex, #GRecMutex and #GRWLock). There is a facility to use
 * individual bits for locks (g_bit_lock()). There are primitives
 * for condition variables to allow synchronization of threads (#GCond).
 * There are primitives for thread-private data - data that every thread
 * has a private instance of (#GPrivate, #GStaticPrivate). There are
 * facilities for one-time initialization (#GOnce, g_once_init_enter()).
 * Finally there are primitives to create and manage threads (#GThread).
 *
 * The threading system is initialized with g_thread_init(), which
 * takes an optional custom thread implementation or %NULL for the
 * default implementation. If you want to call g_thread_init() with a
 * non-%NULL argument this must be done before executing any other GLib
 * functions (except g_mem_set_vtable()). This is a requirement even if
 * no threads are in fact ever created by the process.
 *
 * Calling g_thread_init() with a %NULL argument is somewhat more
 * relaxed. You may call any other glib functions in the main thread
 * before g_thread_init() as long as g_thread_init() is not called from
 * a glib callback, or with any locks held. However, many libraries
 * above glib does not support late initialization of threads, so doing
 * this should be avoided if possible.
 *
 * Please note that since version 2.24 the GObject initialization
 * function g_type_init() initializes threads (with a %NULL argument),
 * so most applications, including those using GTK+ will run with
 * threads enabled. If you want a special thread implementation, make
 * sure you call g_thread_init() before g_type_init() is called.
 *
 * After calling g_thread_init(), GLib is completely thread safe (all
 * global data is automatically locked), but individual data structure
 * instances are not automatically locked for performance reasons. So,
 * for example you must coordinate accesses to the same #GHashTable
 * from multiple threads. The two notable exceptions from this rule
 * are #GMainLoop and #GAsyncQueue, which <emphasis>are</emphasis>
 * threadsafe and need no further application-level locking to be
 * accessed from multiple threads.
 */

/**
 * G_THREADS_IMPL_POSIX:
 *
 * This macro is defined if POSIX style threads are used.
 */

/**
 * G_THREADS_IMPL_WIN32:
 *
 * This macro is defined if Windows style threads are used.
 */

/**
 * G_THREADS_ENABLED:
 *
 * This macro is defined, for backward compatibility, to indicate that
 * GLib has been compiled with thread support. As of GLib 2.28, it is
 * always defined.
 **/

/* G_LOCK Documentation {{{1 ---------------------------------------------- */

/* IMPLEMENTATION NOTE:
 *
 * G_LOCK_DEFINE and friends are convenience macros defined in
 * gthread.h.  Their documentation lives here.
 */

/**
 * G_LOCK_DEFINE:
 * @name: the name of the lock.
 *
 * The %G_LOCK_* macros provide a convenient interface to #GStaticMutex
 * with the advantage that they will expand to nothing in programs
 * compiled against a thread-disabled GLib, saving code and memory
 * there. #G_LOCK_DEFINE defines a lock. It can appear anywhere
 * variable definitions may appear in programs, i.e. in the first block
 * of a function or outside of functions. The @name parameter will be
 * mangled to get the name of the #GStaticMutex. This means that you
 * can use names of existing variables as the parameter - e.g. the name
 * of the variable you intent to protect with the lock. Look at our
 * <function>give_me_next_number()</function> example using the
 * %G_LOCK_* macros:
 *
 * <example>
 *  <title>Using the %G_LOCK_* convenience macros</title>
 *  <programlisting>
 *   G_LOCK_DEFINE (current_number);
 *
 *   int
 *   give_me_next_number (void)
 *   {
 *     static int current_number = 0;
 *     int ret_val;
 *
 *     G_LOCK (current_number);
 *     ret_val = current_number = calc_next_number (current_number);
 *     G_UNLOCK (current_number);
 *
 *     return ret_val;
 *   }
 *  </programlisting>
 * </example>
 **/

/**
 * G_LOCK_DEFINE_STATIC:
 * @name: the name of the lock.
 *
 * This works like #G_LOCK_DEFINE, but it creates a static object.
 **/

/**
 * G_LOCK_EXTERN:
 * @name: the name of the lock.
 *
 * This declares a lock, that is defined with #G_LOCK_DEFINE in another
 * module.
 **/

/**
 * G_LOCK:
 * @name: the name of the lock.
 *
 * Works like g_mutex_lock(), but for a lock defined with
 * #G_LOCK_DEFINE.
 **/

/**
 * G_TRYLOCK:
 * @name: the name of the lock.
 * @Returns: %TRUE, if the lock could be locked.
 *
 * Works like g_mutex_trylock(), but for a lock defined with
 * #G_LOCK_DEFINE.
 **/

/**
 * G_UNLOCK:
 * @name: the name of the lock.
 *
 * Works like g_mutex_unlock(), but for a lock defined with
 * #G_LOCK_DEFINE.
 **/


/* GMutex Documentation {{{1 ------------------------------------------ */

/**
 * GMutex:
 *
 * The #GMutex struct is an opaque data structure to represent a mutex
 * (mutual exclusion). It can be used to protect data against shared
 * access. Take for example the following function:
 *
 * <example>
 *  <title>A function which will not work in a threaded environment</title>
 *  <programlisting>
 *   int
 *   give_me_next_number (void)
 *   {
 *     static int current_number = 0;
 *
 *     /<!-- -->* now do a very complicated calculation to calculate the new
 *      * number, this might for example be a random number generator
 *      *<!-- -->/
 *     current_number = calc_next_number (current_number);
 *
 *     return current_number;
 *   }
 *  </programlisting>
 * </example>
 *
 * It is easy to see that this won't work in a multi-threaded
 * application. There current_number must be protected against shared
 * access. A first naive implementation would be:
 *
 * <example>
 *  <title>The wrong way to write a thread-safe function</title>
 *  <programlisting>
 *   int
 *   give_me_next_number (void)
 *   {
 *     static int current_number = 0;
 *     int ret_val;
 *     static GMutex * mutex = NULL;
 *
 *     if (!mutex) mutex = g_mutex_new (<!-- -->);
 *
 *     g_mutex_lock (mutex);
 *     ret_val = current_number = calc_next_number (current_number);
 *     g_mutex_unlock (mutex);
 *
 *     return ret_val;
 *   }
 *  </programlisting>
 * </example>
 *
 * This looks like it would work, but there is a race condition while
 * constructing the mutex and this code cannot work reliable. Please do
 * not use such constructs in your own programs! One working solution
 * is:
 *
 * <example>
 *  <title>A correct thread-safe function</title>
 *  <programlisting>
 *   static GMutex *give_me_next_number_mutex = NULL;
 *
 *   /<!-- -->* this function must be called before any call to
 *    * give_me_next_number(<!-- -->)
 *    *
 *    * it must be called exactly once.
 *    *<!-- -->/
 *   void
 *   init_give_me_next_number (void)
 *   {
 *     g_assert (give_me_next_number_mutex == NULL);
 *     give_me_next_number_mutex = g_mutex_new (<!-- -->);
 *   }
 *
 *   int
 *   give_me_next_number (void)
 *   {
 *     static int current_number = 0;
 *     int ret_val;
 *
 *     g_mutex_lock (give_me_next_number_mutex);
 *     ret_val = current_number = calc_next_number (current_number);
 *     g_mutex_unlock (give_me_next_number_mutex);
 *
 *     return ret_val;
 *   }
 *  </programlisting>
 * </example>
 *
 * A statically initialized #GMutex provides an even simpler and safer
 * way of doing this:
 *
 * <example>
 *  <title>Using a statically allocated mutex</title>
 *  <programlisting>
 *   int
 *   give_me_next_number (void)
 *   {
 *     static GMutex mutex = G_MUTEX_INIT;
 *     static int current_number = 0;
 *     int ret_val;
 *
 *     g_mutex_lock (&amp;mutex);
 *     ret_val = current_number = calc_next_number (current_number);
 *     g_mutex_unlock (&amp;mutex);
 *
 *     return ret_val;
 *   }
 *  </programlisting>
 * </example>
 *
 * A #GMutex should only be accessed via <function>g_mutex_</function>
 * functions.
 */

/**
 * G_MUTEX_INIT:
 *
 * Initializer for statically allocated #GMutexes.
 * Alternatively, g_mutex_init() can be used.
 *
 * |[
 *   GMutex mutex = G_MUTEX_INIT;
 * ]|
 *
 * Since: 2.32
 */

/* GRecMutex Documentation {{{1 -------------------------------------- */

/**
 * GRecMutex:
 *
 * The GRecMutex struct is an opaque data structure to represent a
 * recursive mutex. It is similar to a #GMutex with the difference
 * that it is possible to lock a GRecMutex multiple times in the same
 * thread without deadlock. When doing so, care has to be taken to
 * unlock the recursive mutex as often as it has been locked.
 *
 * A GRecMutex should only be accessed with the
 * <function>g_rec_mutex_</function> functions. Before a GRecMutex
 * can be used, it has to be initialized with #G_REC_MUTEX_INIT or
 * g_rec_mutex_init().
 *
 * Since: 2.32
 */

/**
 * G_REC_MUTEX_INIT:
 *
 * Initializer for statically allocated #GRecMutexes.
 * Alternatively, g_rec_mutex_init() can be used.
 *
 * |[
 *   GRecMutex mutex = G_REC_MUTEX_INIT;
 * ]|
 *
 * Since: 2.32
 */

/* GRWLock Documentation {{{1 ---------------------------------------- */

/**
 * GRWLock:
 *
 * The GRWLock struct is an opaque data structure to represent a
 * reader-writer lock. It is similar to a #GMutex in that it allows
 * multiple threads to coordinate access to a shared resource.
 *
 * The difference to a mutex is that a reader-writer lock discriminates
 * between read-only ('reader') and full ('writer') access. While only
 * one thread at a time is allowed write access (by holding the 'writer'
 * lock via g_rw_lock_writer_lock()), multiple threads can gain
 * simultaneous read-only access (by holding the 'reader' lock via
 * g_rw_lock_reader_lock()).
 *
 * <example>
 *  <title>An array with access functions</title>
 *  <programlisting>
 *   GRWLock lock = G_RW_LOCK_INIT;
 *   GPtrArray *array;
 *
 *   gpointer
 *   my_array_get (guint index)
 *   {
 *     gpointer retval = NULL;
 *
 *     if (!array)
 *       return NULL;
 *
 *     g_rw_lock_reader_lock (&amp;lock);
 *     if (index &lt; array->len)
 *       retval = g_ptr_array_index (array, index);
 *     g_rw_lock_reader_unlock (&amp;lock);
 *
 *     return retval;
 *   }
 *
 *   void
 *   my_array_set (guint index, gpointer data)
 *   {
 *     g_rw_lock_writer_lock (&amp;lock);
 *
 *     if (!array)
 *       array = g_ptr_array_new (<!-- -->);
 *
 *     if (index >= array->len)
 *       g_ptr_array_set_size (array, index+1);
 *     g_ptr_array_index (array, index) = data;
 *
 *     g_rw_lock_writer_unlock (&amp;lock);
 *   }
 *  </programlisting>
 *  <para>
 *    This example shows an array which can be accessed by many readers
 *    (the <function>my_array_get()</function> function) simultaneously,
 *    whereas the writers (the <function>my_array_set()</function>
 *    function) will only be allowed once at a time and only if no readers
 *    currently access the array. This is because of the potentially
 *    dangerous resizing of the array. Using these functions is fully
 *    multi-thread safe now.
 *  </para>
 * </example>
 *
 * A GRWLock should only be accessed with the
 * <function>g_rw_lock_</function> functions. Before it can be used,
 * it has to be initialized with #G_RW_LOCK_INIT or g_rw_lock_init().
 *
 * Since: 2.32
 */

/**
 * G_RW_LOCK_INIT:
 *
 * Initializer for statically allocated #GRWLocks.
 * Alternatively, g_rw_lock_init_init() can be used.
 *
 * |[
 *   GRWLock lock = G_RW_LOCK_INIT;
 * ]|
 *
 * Since: 2.32
 */

/* GCond Documentation {{{1 ------------------------------------------ */

/**
 * GCond:
 *
 * The #GCond struct is an opaque data structure that represents a
 * condition. Threads can block on a #GCond if they find a certain
 * condition to be false. If other threads change the state of this
 * condition they signal the #GCond, and that causes the waiting
 * threads to be woken up.
 *
 * <example>
 *  <title>
 *   Using GCond to block a thread until a condition is satisfied
 *  </title>
 *  <programlisting>
 *   GCond* data_cond = NULL; /<!-- -->* Must be initialized somewhere *<!-- -->/
 *   GMutex* data_mutex = NULL; /<!-- -->* Must be initialized somewhere *<!-- -->/
 *   gpointer current_data = NULL;
 *
 *   void
 *   push_data (gpointer data)
 *   {
 *     g_mutex_lock (data_mutex);
 *     current_data = data;
 *     g_cond_signal (data_cond);
 *     g_mutex_unlock (data_mutex);
 *   }
 *
 *   gpointer
 *   pop_data (void)
 *   {
 *     gpointer data;
 *
 *     g_mutex_lock (data_mutex);
 *     while (!current_data)
 *       g_cond_wait (data_cond, data_mutex);
 *     data = current_data;
 *     current_data = NULL;
 *     g_mutex_unlock (data_mutex);
 *
 *     return data;
 *   }
 *  </programlisting>
 * </example>
 *
 * Whenever a thread calls pop_data() now, it will wait until
 * current_data is non-%NULL, i.e. until some other thread
 * has called push_data().
 *
 * <note><para>It is important to use the g_cond_wait() and
 * g_cond_timed_wait() functions only inside a loop which checks for the
 * condition to be true.  It is not guaranteed that the waiting thread
 * will find the condition fulfilled after it wakes up, even if the
 * signaling thread left the condition in that state: another thread may
 * have altered the condition before the waiting thread got the chance
 * to be woken up, even if the condition itself is protected by a
 * #GMutex, like above.</para></note>
 *
 * A #GCond should only be accessed via the <function>g_cond_</function>
 * functions.
 */

/**
 * G_COND_INIT:
 *
 * Initializer for statically allocated #GConds.
 * Alternatively, g_cond_init() can be used.
 *
 * |[
 *   GCond cond = G_COND_INIT;
 * ]|
 *
 * Since: 2.32
 */

/* GPrivate Documentation {{{1 --------------------------------------- */

/**
 * GPrivate:
 *
 * <note><para>
 * #GStaticPrivate is a better choice for most uses.
 * </para></note>
 *
 * The #GPrivate struct is an opaque data structure to represent a
 * thread private data key. Threads can thereby obtain and set a
 * pointer which is private to the current thread. Take our
 * <function>give_me_next_number(<!-- -->)</function> example from
 * above.  Suppose we don't want <literal>current_number</literal> to be
 * shared between the threads, but instead to be private to each thread.
 * This can be done as follows:
 *
 * <example>
 *  <title>Using GPrivate for per-thread data</title>
 *  <programlisting>
 *   GPrivate* current_number_key = NULL; /<!-- -->* Must be initialized somewhere
 *                                           with g_private_new (g_free); *<!-- -->/
 *
 *   int
 *   give_me_next_number (void)
 *   {
 *     int *current_number = g_private_get (current_number_key);
 *
 *     if (!current_number)
 *       {
 *         current_number = g_new (int, 1);
 *         *current_number = 0;
 *         g_private_set (current_number_key, current_number);
 *       }
 *
 *     *current_number = calc_next_number (*current_number);
 *
 *     return *current_number;
 *   }
 *  </programlisting>
 * </example>
 *
 * Here the pointer belonging to the key
 * <literal>current_number_key</literal> is read. If it is %NULL, it has
 * not been set yet. Then get memory for an integer value, assign this
 * memory to the pointer and write the pointer back. Now we have an
 * integer value that is private to the current thread.
 *
 * The #GPrivate struct should only be accessed via the
 * <function>g_private_</function> functions.
 */

/* GThread Documentation {{{1 ---------------------------------------- */
/**
 * GThread:
 *
 * The #GThread struct represents a running thread. It has three public
 * read-only members, but the underlying struct is bigger, so you must
 * not copy this struct.
 *
 * <note><para>Resources for a joinable thread are not fully released
 * until g_thread_join() is called for that thread.</para></note>
 **/

/**
 * GThreadFunc:
 * @data: data passed to the thread.
 * @Returns: the return value of the thread, which will be returned by
 *           g_thread_join().
 *
 * Specifies the type of the @func functions passed to
 * g_thread_create() or g_thread_create_full().
 **/

/* GThreadError {{{1 ------------------------------------------------------- */
/**
 * GThreadError:
 * @G_THREAD_ERROR_AGAIN: a thread couldn't be created due to resource
 *                        shortage. Try again later.
 *
 * Possible errors of thread related functions.
 **/

/**
 * G_THREAD_ERROR:
 *
 * The error domain of the GLib thread subsystem.
 **/
GQuark
g_thread_error_quark (void)
{
  return g_quark_from_static_string ("g_thread_error");
}

/* Miscellaneous Structures {{{1 ------------------------------------------ */

typedef struct _GRealThread GRealThread;
struct  _GRealThread
{
  GThread thread;
  /* Bit 0 protects private_data. To avoid deadlocks, do not block while
   * holding this (particularly on the g_thread lock). */
  volatile gint private_data_lock;
  GArray *private_data;
  GRealThread *next;
  gpointer retval;
  GSystemThread system_thread;
};

#define LOCK_PRIVATE_DATA(self)   g_bit_lock (&(self)->private_data_lock, 0)
#define UNLOCK_PRIVATE_DATA(self) g_bit_unlock (&(self)->private_data_lock, 0)

static void    g_thread_cleanup (gpointer data);

/**
 * g_thread_supported:
 * @Returns: %TRUE, if the thread system is initialized.
 *
 * This function returns %TRUE if the thread system is initialized, and
 * %FALSE if it is not.
 *
 * <note><para>This function is actually a macro. Apart from taking the
 * address of it you can however use it as if it was a
 * function.</para></note>
 **/
/* Local Data {{{1 -------------------------------------------------------- */

gboolean         g_threads_got_initialized = FALSE;
GSystemThread    zero_thread; /* This is initialized to all zero */
GMutex           g_once_mutex = G_MUTEX_INIT;

static GCond     g_once_cond = G_COND_INIT;
static GPrivate  g_thread_specific_private;
static GRealThread *g_thread_all_threads = NULL;
static GSList   *g_thread_free_indices = NULL;
static GSList*   g_once_init_list = NULL;

G_LOCK_DEFINE_STATIC (g_thread);

/* Initialisation {{{1 ---------------------------------------------------- */

/**
 * g_thread_init:
 * @vtable: a function table of type #GThreadFunctions, that provides
 *     the entry points to the thread system to be used. Since 2.32,
 *     this parameter is ignored and should always be %NULL
 *
 * If you use GLib from more than one thread, you must initialize the
 * thread system by calling g_thread_init().
 *
 * Since version 2.24, calling g_thread_init() multiple times is allowed,
 * but nothing happens except for the first call.
 *
 * Since version 2.32, GLib does not support custom thread implementations
 * anymore and the @vtable parameter is ignored and you should pass %NULL.
 *
 * <note><para>g_thread_init() must not be called directly or indirectly
 * in a callback from GLib. Also no mutexes may be currently locked while
 * calling g_thread_init().</para></note>
 *
 * <note><para>To use g_thread_init() in your program, you have to link
 * with the libraries that the command <command>pkg-config --libs
 * gthread-2.0</command> outputs. This is not the case for all the
 * other thread-related functions of GLib. Those can be used without
 * having to link with the thread libraries.</para></note>
 */

void
g_thread_init_glib (void)
{
  static gboolean already_done;
  GRealThread* main_thread;

  if (already_done)
    return;

  already_done = TRUE;

  /* We let the main thread (the one that calls g_thread_init) inherit
   * the static_private data set before calling g_thread_init
   */
  main_thread = (GRealThread*) g_thread_self ();

  /* setup the basic threading system */
  g_threads_got_initialized = TRUE;
  g_private_init (&g_thread_specific_private, g_thread_cleanup);
  g_private_set (&g_thread_specific_private, main_thread);
  g_system_thread_self (&main_thread->system_thread);

  /* accomplish log system initialization to enable messaging */
  _g_messages_thread_init_nomessage ();
}

/* GOnce {{{1 ------------------------------------------------------------- */

/**
 * GOnce:
 * @status: the status of the #GOnce
 * @retval: the value returned by the call to the function, if @status
 *          is %G_ONCE_STATUS_READY
 *
 * A #GOnce struct controls a one-time initialization function. Any
 * one-time initialization function must have its own unique #GOnce
 * struct.
 *
 * Since: 2.4
 **/

/**
 * G_ONCE_INIT:
 *
 * A #GOnce must be initialized with this macro before it can be used.
 *
 * <informalexample>
 *  <programlisting>
 *   GOnce my_once = G_ONCE_INIT;
 *  </programlisting>
 * </informalexample>
 *
 * Since: 2.4
 **/

/**
 * GOnceStatus:
 * @G_ONCE_STATUS_NOTCALLED: the function has not been called yet.
 * @G_ONCE_STATUS_PROGRESS: the function call is currently in progress.
 * @G_ONCE_STATUS_READY: the function has been called.
 *
 * The possible statuses of a one-time initialization function
 * controlled by a #GOnce struct.
 *
 * Since: 2.4
 **/

/**
 * g_once:
 * @once: a #GOnce structure
 * @func: the #GThreadFunc function associated to @once. This function
 *        is called only once, regardless of the number of times it and
 *        its associated #GOnce struct are passed to g_once().
 * @arg: data to be passed to @func
 *
 * The first call to this routine by a process with a given #GOnce
 * struct calls @func with the given argument. Thereafter, subsequent
 * calls to g_once()  with the same #GOnce struct do not call @func
 * again, but return the stored result of the first call. On return
 * from g_once(), the status of @once will be %G_ONCE_STATUS_READY.
 *
 * For example, a mutex or a thread-specific data key must be created
 * exactly once. In a threaded environment, calling g_once() ensures
 * that the initialization is serialized across multiple threads.
 *
 * <note><para>Calling g_once() recursively on the same #GOnce struct in
 * @func will lead to a deadlock.</para></note>
 *
 * <informalexample>
 *  <programlisting>
 *   gpointer
 *   get_debug_flags (void)
 *   {
 *     static GOnce my_once = G_ONCE_INIT;
 *
 *     g_once (&my_once, parse_debug_flags, NULL);
 *
 *     return my_once.retval;
 *   }
 *  </programlisting>
 * </informalexample>
 *
 * Since: 2.4
 **/
gpointer
g_once_impl (GOnce       *once,
             GThreadFunc  func,
             gpointer     arg)
{
  g_mutex_lock (&g_once_mutex);

  while (once->status == G_ONCE_STATUS_PROGRESS)
    g_cond_wait (&g_once_cond, &g_once_mutex);

  if (once->status != G_ONCE_STATUS_READY)
    {
      once->status = G_ONCE_STATUS_PROGRESS;
      g_mutex_unlock (&g_once_mutex);

      once->retval = func (arg);

      g_mutex_lock (&g_once_mutex);
      once->status = G_ONCE_STATUS_READY;
      g_cond_broadcast (&g_once_cond);
    }

  g_mutex_unlock (&g_once_mutex);

  return once->retval;
}

/**
 * g_once_init_enter:
 * @value_location: location of a static initializable variable
 *                  containing 0.
 * @Returns: %TRUE if the initialization section should be entered,
 *           %FALSE and blocks otherwise
 *
 * Function to be called when starting a critical initialization
 * section. The argument @value_location must point to a static
 * 0-initialized variable that will be set to a value other than 0 at
 * the end of the initialization section. In combination with
 * g_once_init_leave() and the unique address @value_location, it can
 * be ensured that an initialization section will be executed only once
 * during a program's life time, and that concurrent threads are
 * blocked until initialization completed. To be used in constructs
 * like this:
 *
 * <informalexample>
 *  <programlisting>
 *   static gsize initialization_value = 0;
 *
 *   if (g_once_init_enter (&amp;initialization_value))
 *     {
 *       gsize setup_value = 42; /<!-- -->* initialization code here *<!-- -->/
 *
 *       g_once_init_leave (&amp;initialization_value, setup_value);
 *     }
 *
 *   /<!-- -->* use initialization_value here *<!-- -->/
 *  </programlisting>
 * </informalexample>
 *
 * Since: 2.14
 **/
gboolean
g_once_init_enter_impl (volatile gsize *value_location)
{
  gboolean need_init = FALSE;
  g_mutex_lock (&g_once_mutex);
  if (g_atomic_pointer_get (value_location) == NULL)
    {
      if (!g_slist_find (g_once_init_list, (void*) value_location))
        {
          need_init = TRUE;
          g_once_init_list = g_slist_prepend (g_once_init_list, (void*) value_location);
        }
      else
        do
          g_cond_wait (&g_once_cond, &g_once_mutex);
        while (g_slist_find (g_once_init_list, (void*) value_location));
    }
  g_mutex_unlock (&g_once_mutex);
  return need_init;
}

/**
 * g_once_init_leave:
 * @value_location: location of a static initializable variable
 *                  containing 0.
 * @initialization_value: new non-0 value for *@value_location.
 *
 * Counterpart to g_once_init_enter(). Expects a location of a static
 * 0-initialized initialization variable, and an initialization value
 * other than 0. Sets the variable to the initialization value, and
 * releases concurrent threads blocking in g_once_init_enter() on this
 * initialization variable.
 *
 * Since: 2.14
 **/
void
g_once_init_leave (volatile gsize *value_location,
                   gsize           initialization_value)
{
  g_return_if_fail (g_atomic_pointer_get (value_location) == NULL);
  g_return_if_fail (initialization_value != 0);
  g_return_if_fail (g_once_init_list != NULL);

  g_atomic_pointer_set (value_location, initialization_value);
  g_mutex_lock (&g_once_mutex);
  g_once_init_list = g_slist_remove (g_once_init_list, (void*) value_location);
  g_cond_broadcast (&g_once_cond);
  g_mutex_unlock (&g_once_mutex);
}

/* GStaticPrivate {{{1 ---------------------------------------------------- */

typedef struct _GStaticPrivateNode GStaticPrivateNode;
struct _GStaticPrivateNode
{
  gpointer       data;
  GDestroyNotify destroy;
};

/**
 * GStaticPrivate:
 *
 * A #GStaticPrivate works almost like a #GPrivate, but it has one
 * significant advantage. It doesn't need to be created at run-time
 * like a #GPrivate, but can be defined at compile-time. This is
 * similar to the difference between #GMutex and #GStaticMutex. Now
 * look at our <function>give_me_next_number()</function> example with
 * #GStaticPrivate:
 *
 * <example>
 *  <title>Using GStaticPrivate for per-thread data</title>
 *  <programlisting>
 *   int
 *   give_me_next_number (<!-- -->)
 *   {
 *     static GStaticPrivate current_number_key = G_STATIC_PRIVATE_INIT;
 *     int *current_number = g_static_private_get (&amp;current_number_key);
 *
 *     if (!current_number)
 *       {
 *         current_number = g_new (int,1);
 *         *current_number = 0;
 *         g_static_private_set (&amp;current_number_key, current_number, g_free);
 *       }
 *
 *     *current_number = calc_next_number (*current_number);
 *
 *     return *current_number;
 *   }
 *  </programlisting>
 * </example>
 **/

/**
 * G_STATIC_PRIVATE_INIT:
 *
 * Every #GStaticPrivate must be initialized with this macro, before it
 * can be used.
 *
 * |[
 *   GStaticPrivate my_private = G_STATIC_PRIVATE_INIT;
 * ]|
 */

/**
 * g_static_private_init:
 * @private_key: a #GStaticPrivate to be initialized.
 *
 * Initializes @private_key. Alternatively you can initialize it with
 * #G_STATIC_PRIVATE_INIT.
 **/
void
g_static_private_init (GStaticPrivate *private_key)
{
  private_key->index = 0;
}

/**
 * g_static_private_get:
 * @private_key: a #GStaticPrivate.
 * @Returns: the corresponding pointer.
 *
 * Works like g_private_get() only for a #GStaticPrivate.
 *
 * This function works even if g_thread_init() has not yet been called.
 */
gpointer
g_static_private_get (GStaticPrivate *private_key)
{
  GRealThread *self = (GRealThread*) g_thread_self ();
  GArray *array;
  gpointer ret = NULL;

  LOCK_PRIVATE_DATA (self);

  array = self->private_data;

  if (array && private_key->index != 0 && private_key->index <= array->len)
    ret = g_array_index (array, GStaticPrivateNode,
                         private_key->index - 1).data;

  UNLOCK_PRIVATE_DATA (self);
  return ret;
}

/**
 * g_static_private_set:
 * @private_key: a #GStaticPrivate.
 * @data: the new pointer.
 * @notify: a function to be called with the pointer whenever the
 *          current thread ends or sets this pointer again.
 *
 * Sets the pointer keyed to @private_key for the current thread and
 * the function @notify to be called with that pointer (%NULL or
 * non-%NULL), whenever the pointer is set again or whenever the
 * current thread ends.
 *
 * This function works even if g_thread_init() has not yet been called.
 * If g_thread_init() is called later, the @data keyed to @private_key
 * will be inherited only by the main thread, i.e. the one that called
 * g_thread_init().
 *
 * <note><para>@notify is used quite differently from @destructor in
 * g_private_new().</para></note>
 */
void
g_static_private_set (GStaticPrivate *private_key,
                      gpointer        data,
                      GDestroyNotify  notify)
{
  GRealThread *self = (GRealThread*) g_thread_self ();
  GArray *array;
  static guint next_index = 0;
  GStaticPrivateNode *node;
  gpointer ddata = NULL;
  GDestroyNotify ddestroy = NULL;

  if (!private_key->index)
    {
      G_LOCK (g_thread);

      if (!private_key->index)
        {
          if (g_thread_free_indices)
            {
              private_key->index =
                GPOINTER_TO_UINT (g_thread_free_indices->data);
              g_thread_free_indices =
                g_slist_delete_link (g_thread_free_indices,
                                     g_thread_free_indices);
            }
          else
            private_key->index = ++next_index;
        }

      G_UNLOCK (g_thread);
    }

  LOCK_PRIVATE_DATA (self);

  array = self->private_data;
  if (!array)
    {
      array = g_array_new (FALSE, TRUE, sizeof (GStaticPrivateNode));
      self->private_data = array;
    }

  if (private_key->index > array->len)
    g_array_set_size (array, private_key->index);

  node = &g_array_index (array, GStaticPrivateNode, private_key->index - 1);

  ddata = node->data;
  ddestroy = node->destroy;

  node->data = data;
  node->destroy = notify;

  UNLOCK_PRIVATE_DATA (self);

  if (ddestroy)
    ddestroy (ddata);
}

/**
 * g_static_private_free:
 * @private_key: a #GStaticPrivate to be freed.
 *
 * Releases all resources allocated to @private_key.
 *
 * You don't have to call this functions for a #GStaticPrivate with an
 * unbounded lifetime, i.e. objects declared 'static', but if you have
 * a #GStaticPrivate as a member of a structure and the structure is
 * freed, you should also free the #GStaticPrivate.
 */
void
g_static_private_free (GStaticPrivate *private_key)
{
  guint idx = private_key->index;
  GRealThread *thread, *next;
  GArray *garbage = NULL;

  if (!idx)
    return;

  private_key->index = 0;

  G_LOCK (g_thread);

  thread = g_thread_all_threads;

  for (thread = g_thread_all_threads; thread; thread = next)
    {
      GArray *array;

      next = thread->next;

      LOCK_PRIVATE_DATA (thread);

      array = thread->private_data;

      if (array && idx <= array->len)
        {
          GStaticPrivateNode *node = &g_array_index (array,
                                                     GStaticPrivateNode,
                                                     idx - 1);
          gpointer ddata = node->data;
          GDestroyNotify ddestroy = node->destroy;

          node->data = NULL;
          node->destroy = NULL;

          if (ddestroy)
            {
              /* defer non-trivial destruction til after we've finished
               * iterating, since we must continue to hold the lock */
              if (garbage == NULL)
                garbage = g_array_new (FALSE, TRUE,
                                       sizeof (GStaticPrivateNode));

              g_array_set_size (garbage, garbage->len + 1);

              node = &g_array_index (garbage, GStaticPrivateNode,
                                     garbage->len - 1);
              node->data = ddata;
              node->destroy = ddestroy;
            }
        }

      UNLOCK_PRIVATE_DATA (thread);
    }
  g_thread_free_indices = g_slist_prepend (g_thread_free_indices,
                                           GUINT_TO_POINTER (idx));
  G_UNLOCK (g_thread);

  if (garbage)
    {
      guint i;

      for (i = 0; i < garbage->len; i++)
        {
          GStaticPrivateNode *node;

          node = &g_array_index (garbage, GStaticPrivateNode, i);
          node->destroy (node->data);
        }

      g_array_free (garbage, TRUE);
    }
}

/* GThread Extra Functions {{{1 ------------------------------------------- */
static void
g_thread_cleanup (gpointer data)
{
  if (data)
    {
      GRealThread* thread = data;
      GArray *array;

      LOCK_PRIVATE_DATA (thread);
      array = thread->private_data;
      thread->private_data = NULL;
      UNLOCK_PRIVATE_DATA (thread);

      if (array)
        {
          guint i;

          for (i = 0; i < array->len; i++ )
            {
              GStaticPrivateNode *node =
                &g_array_index (array, GStaticPrivateNode, i);
              if (node->destroy)
                node->destroy (node->data);
            }
          g_array_free (array, TRUE);
        }

      /* We only free the thread structure, if it isn't joinable. If
         it is, the structure is freed in g_thread_join */
      if (!thread->thread.joinable)
        {
          GRealThread *t, *p;

          G_LOCK (g_thread);
          for (t = g_thread_all_threads, p = NULL; t; p = t, t = t->next)
            {
              if (t == thread)
                {
                  if (p)
                    p->next = t->next;
                  else
                    g_thread_all_threads = t->next;
                  break;
                }
            }
          G_UNLOCK (g_thread);

          /* Just to make sure, this isn't used any more */
          g_system_thread_assign (thread->system_thread, zero_thread);
          g_free (thread);
        }
    }
}

static gpointer
g_thread_create_proxy (gpointer data)
{
  GRealThread* thread = data;

  g_assert (data);

  /* This has to happen before G_LOCK, as that might call g_thread_self */
  g_private_set (&g_thread_specific_private, data);

  /* the lock makes sure, that thread->system_thread is written,
   * before thread->thread.func is called. See g_thread_create.
   */
  G_LOCK (g_thread);
  G_UNLOCK (g_thread);

  thread->retval = thread->thread.func (thread->thread.data);

  return NULL;
}

/**
 * g_thread_create:
 * @func: a function to execute in the new thread
 * @data: an argument to supply to the new thread
 * @joinable: should this thread be joinable?
 * @error: return location for error, or %NULL
 *
 * This function creates a new thread.
 *
 * If @joinable is %TRUE, you can wait for this threads termination
 * calling g_thread_join(). Otherwise the thread will just disappear
 * when it terminates.
 *
 * The new thread executes the function @func with the argument @data.
 * If the thread was created successfully, it is returned.
 *
 * @error can be %NULL to ignore errors, or non-%NULL to report errors.
 * The error is set, if and only if the function returns %NULL.
 *
 * Returns: the new #GThread on success
 */
GThread *
g_thread_create (GThreadFunc   func,
                 gpointer      data,
                 gboolean      joinable,
                 GError      **error)
{
  return g_thread_create_with_stack_size (func, data, joinable, 0, error);
}

/**
 * g_thread_create_with_stack_size:
 * @func: a function to execute in the new thread.
 * @data: an argument to supply to the new thread.
 * @joinable: should this thread be joinable?
 * @stack_size: a stack size for the new thread.
 * @error: return location for error.
 * @Returns: the new #GThread on success.
 *
 * This function creates a new thread. If the underlying thread
 * implementation supports it, the thread gets a stack size of
 * @stack_size or the default value for the current platform, if
 * @stack_size is 0.
 *
 * If @joinable is %TRUE, you can wait for this threads termination
 * calling g_thread_join(). Otherwise the thread will just disappear
 * when it terminates.
 *
 * The new thread executes the function @func with the argument @data.
 * If the thread was created successfully, it is returned.
 *
 * @error can be %NULL to ignore errors, or non-%NULL to report errors.
 * The error is set, if and only if the function returns %NULL.
 *
 * <note><para>
 *   Only use g_thread_create_with_stack_size() if you really can't use
 *   g_thread_create() instead. g_thread_create() does not take
 *   @stack_size, as it should only be used in cases in which it is
 *   unavoidable.
 * </para></note>
 **/
GThread*
g_thread_create_with_stack_size (GThreadFunc   func,
                                 gpointer      data,
                                 gboolean      joinable,
                                 gsize         stack_size,
                                 GError      **error)
{
  GRealThread* result;
  GError *local_error = NULL;
  g_return_val_if_fail (func, NULL);

  result = g_new0 (GRealThread, 1);

  result->thread.joinable = joinable;
  result->thread.func = func;
  result->thread.data = data;
  result->private_data = NULL;
  G_LOCK (g_thread);
  g_system_thread_create (g_thread_create_proxy, result,
                          stack_size, joinable,
                          &result->system_thread, &local_error);
  if (!local_error)
    {
      result->next = g_thread_all_threads;
      g_thread_all_threads = result;
    }
  G_UNLOCK (g_thread);

  if (local_error)
    {
      g_propagate_error (error, local_error);
      g_free (result);
      return NULL;
    }

  return (GThread*) result;
}

/**
 * g_thread_exit:
 * @retval: the return value of this thread.
 *
 * Exits the current thread. If another thread is waiting for that
 * thread using g_thread_join() and the current thread is joinable, the
 * waiting thread will be woken up and get @retval as the return value
 * of g_thread_join(). If the current thread is not joinable, @retval
 * is ignored. Calling
 *
 * |[
 *   g_thread_exit (retval);
 * ]|
 *
 * is equivalent to returning @retval from the function @func, as given
 * to g_thread_create().
 *
 * <note><para>Never call g_thread_exit() from within a thread of a
 * #GThreadPool, as that will mess up the bookkeeping and lead to funny
 * and unwanted results.</para></note>
 **/
void
g_thread_exit (gpointer retval)
{
  GRealThread* real = (GRealThread*) g_thread_self ();
  real->retval = retval;

  g_system_thread_exit ();
}

/**
 * g_thread_join:
 * @thread: a #GThread to be waited for.
 * @Returns: the return value of the thread.
 *
 * Waits until @thread finishes, i.e. the function @func, as given to
 * g_thread_create(), returns or g_thread_exit() is called by @thread.
 * All resources of @thread including the #GThread struct are released.
 * @thread must have been created with @joinable=%TRUE in
 * g_thread_create(). The value returned by @func or given to
 * g_thread_exit() by @thread is returned by this function.
 **/
gpointer
g_thread_join (GThread* thread)
{
  GRealThread* real = (GRealThread*) thread;
  GRealThread *p, *t;
  gpointer retval;

  g_return_val_if_fail (thread, NULL);
  g_return_val_if_fail (thread->joinable, NULL);
  g_return_val_if_fail (!g_system_thread_equal (&real->system_thread, &zero_thread), NULL);

  g_system_thread_join (&real->system_thread);

  retval = real->retval;

  G_LOCK (g_thread);
  for (t = g_thread_all_threads, p = NULL; t; p = t, t = t->next)
    {
      if (t == (GRealThread*) thread)
        {
          if (p)
            p->next = t->next;
          else
            g_thread_all_threads = t->next;
          break;
        }
    }
  G_UNLOCK (g_thread);

  /* Just to make sure, this isn't used any more */
  thread->joinable = 0;
  g_system_thread_assign (real->system_thread, zero_thread);

  /* the thread structure for non-joinable threads is freed upon
   * thread end. We free the memory here. This will leave a loose end,
   * if a joinable thread is not joined.
   */
  g_free (thread);

  return retval;
}

/**
 * g_thread_self:
 * @Returns: the current thread.
 *
 * This functions returns the #GThread corresponding to the calling
 * thread.
 **/
GThread*
g_thread_self (void)
{
  GRealThread* thread = g_private_get (&g_thread_specific_private);

  if (!thread)
    {
      /* If no thread data is available, provide and set one.  This
         can happen for the main thread and for threads, that are not
         created by GLib. */
      thread = g_new0 (GRealThread, 1);
      thread->thread.joinable = FALSE; /* This is a save guess */
      thread->thread.func = NULL;
      thread->thread.data = NULL;
      thread->private_data = NULL;

      g_system_thread_self (&thread->system_thread);

      g_private_set (&g_thread_specific_private, thread);

      G_LOCK (g_thread);
      thread->next = g_thread_all_threads;
      g_thread_all_threads = thread;
      G_UNLOCK (g_thread);
    }

  return (GThread*)thread;
}

/* Unsorted {{{1 ---------------------------------------------------------- */

/**
 * g_thread_foreach
 * @thread_func: function to call for all GThread structures
 * @user_data:   second argument to @thread_func
 *
 * Call @thread_func on all existing #GThread structures. Note that
 * threads may decide to exit while @thread_func is running, so
 * without intimate knowledge about the lifetime of foreign threads,
 * @thread_func shouldn't access the GThread* pointer passed in as
 * first argument. However, @thread_func will not be called for threads
 * which are known to have exited already.
 *
 * Due to thread lifetime checks, this function has an execution complexity
 * which is quadratic in the number of existing threads.
 *
 * Since: 2.10
 */
void
g_thread_foreach (GFunc    thread_func,
                  gpointer user_data)
{
  GSList *slist = NULL;
  GRealThread *thread;
  g_return_if_fail (thread_func != NULL);
  /* snapshot the list of threads for iteration */
  G_LOCK (g_thread);
  for (thread = g_thread_all_threads; thread; thread = thread->next)
    slist = g_slist_prepend (slist, thread);
  G_UNLOCK (g_thread);
  /* walk the list, skipping non-existent threads */
  while (slist)
    {
      GSList *node = slist;
      slist = node->next;
      /* check whether the current thread still exists */
      G_LOCK (g_thread);
      for (thread = g_thread_all_threads; thread; thread = thread->next)
        if (thread == node->data)
          break;
      G_UNLOCK (g_thread);
      if (thread)
        thread_func (thread, user_data);
      g_slist_free_1 (node);
    }
}

/**
 * g_thread_get_initialized:
 *
 * Indicates if g_thread_init() has been called.
 *
 * Returns: %TRUE if threads have been initialized.
 *
 * Since: 2.20
 */
gboolean
g_thread_get_initialized ()
{
  return g_thread_supported ();
}

/**
 * g_mutex_new:
 *
 * Allocated and initializes a new #GMutex.
 *
 * Returns: a newly allocated #GMutex. Use g_mutex_free() to free
 */
GMutex *
g_mutex_new (void)
{
  GMutex *mutex;

  mutex = g_slice_new (GMutex);
  g_mutex_init (mutex);

  return mutex;
}

/**
 * g_mutex_free:
 * @mutex: a #GMutex
 *
 * Destroys a @mutex that has been created with g_mutex_new().
 *
 * Calling g_mutex_free() on a locked mutex may result
 * in undefined behaviour.
 */
void
g_mutex_free (GMutex *mutex)
{
  g_mutex_clear (mutex);
  g_slice_free (GMutex, mutex);
}

/**
 * g_cond_new:
 *
 * Allocates and initializes a new #GCond.
 *
 * Returns: a newly allocated #GCond. Free with g_cond_free()
 */
GCond *
g_cond_new (void)
{
  GCond *cond;

  cond = g_slice_new (GCond);
  g_cond_init (cond);

  return cond;
}

/**
 * g_cond_free:
 * @cond: a #GCond
 *
 * Destroys a #GCond that has been created with g_cond_new().
 */
void
g_cond_free (GCond *cond)
{
  g_cond_clear (cond);
  g_slice_free (GCond, cond);
}

/**
 * g_private_new:
 * @destructor: a function to destroy the data keyed to
 *     the #GPrivate when a thread ends
 *
 * Creates a new #GPrivate. If @destructor is non-%NULL, it is a
 * pointer to a destructor function. Whenever a thread ends and the
 * corresponding pointer keyed to this instance of #GPrivate is
 * non-%NULL, the destructor is called with this pointer as the
 * argument.
 *
 * <note><para>
 * #GStaticPrivate is a better choice for most uses.
 * </para></note>
 *
 * <note><para>@destructor is used quite differently from @notify in
 * g_static_private_set().</para></note>
 *
 * <note><para>A #GPrivate cannot be freed. Reuse it instead, if you
 * can, to avoid shortage, or use #GStaticPrivate.</para></note>
 *
 * <note><para>This function will abort if g_thread_init() has not been
 * called yet.</para></note>
 *
 * Returns: a newly allocated #GPrivate
 */
GPrivate *
g_private_new (GDestroyNotify notify)
{
  GPrivate *key;

  key = g_slice_new (GPrivate);
  g_private_init (key, notify);

  return key;
}

/* vim: set foldmethod=marker: */