--- /dev/null
+/*
+ * Copyright © 2008 Ryan Lortie
+ * Copyright © 2010 Codethink Limited
+ *
+ * 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 licence, 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.
+ *
+ * Author: Ryan Lortie <desrt@desrt.ca>
+ */
+
+#include "gbitlock.h"
+
+#include <glib/gatomic.h>
+#include <glib/gslist.h>
+#include <glib/gthread.h>
+
+#include "gthreadprivate.h"
+#include "config.h"
+
+#include "galias.h"
+
+#ifndef HAVE_FUTEX
+static GSList *g_futex_address_list = NULL;
+static GMutex *g_futex_mutex = NULL;
+#endif
+
+void
+_g_futex_thread_init (void) {
+#ifndef HAVE_FUTEX
+ g_futex_mutex = g_mutex_new ();
+#endif
+}
+
+#ifdef HAVE_FUTEX
+/*
+ * We have headers for futex(2) on the build machine. This does not
+ * imply that every system that ever runs the resulting glib will have
+ * kernel support for futex, but you'd have to have a pretty old
+ * kernel in order for that not to be the case.
+ *
+ * If anyone actually gets bit by this, please file a bug. :)
+ */
+#include <linux/futex.h>
+#include <syscall.h>
+#include <unistd.h>
+
+/* < private >
+ * g_futex_wait:
+ * @address: a pointer to an integer
+ * @value: the value that should be at @address
+ *
+ * Atomically checks that the value stored at @address is equal to
+ * @value and then blocks. If the value stored at @address is not
+ * equal to @value then this function returns immediately.
+ *
+ * To unblock, call g_futex_wake() on @address.
+ *
+ * This call may spuriously unblock (for example, in response to the
+ * process receiving a signal) but this is not guaranteed. Unlike the
+ * Linux system call of a similar name, there is no guarantee that a
+ * waiting process will unblock due to a g_futex_wake() call in a
+ * separate process.
+ */
+static void
+g_futex_wait (const volatile gint *address,
+ gint value)
+{
+ syscall (SYS_futex, address, (gsize) FUTEX_WAIT, (gsize) value, NULL);
+}
+
+/* < private >
+ * g_futex_wake:
+ * @address: a pointer to an integer
+ *
+ * Nominally, wakes one thread that is blocked in g_futex_wait() on
+ * @address (if any thread is currently waiting).
+ *
+ * As mentioned in the documention for g_futex_wait(), spurious
+ * wakeups may occur. As such, this call may result in more than one
+ * thread being woken up.
+ */
+static void
+g_futex_wake (const volatile gint *address)
+{
+ syscall (SYS_futex, address, (gsize) FUTEX_WAKE, (gsize) 1, NULL);
+}
+
+#else
+
+/* emulate futex(2) */
+typedef struct
+{
+ const volatile gint *address;
+ gint ref_count;
+ GCond *wait_queue;
+} WaitAddress;
+
+static GSList *g_futex_address_list;
+static GMutex *g_futex_mutex;
+
+static WaitAddress *
+g_futex_find_address (const volatile gint *address)
+{
+ GSList *node;
+
+ for (node = g_futex_address_list; node; node = node->next)
+ {
+ WaitAddress *waiter = node->data;
+
+ if (waiter->address == address)
+ return waiter;
+ }
+
+ return NULL;
+}
+
+static void
+g_futex_wait (const volatile gint *address,
+ gint value)
+{
+ g_mutex_lock (g_futex_mutex);
+ if G_LIKELY (g_atomic_int_get (address) == value)
+ {
+ WaitAddress *waiter;
+
+ if ((waiter = g_futex_find_address (address)) == NULL)
+ {
+ waiter = g_slice_new (WaitAddress);
+ waiter->address = address;
+ waiter->wait_queue = g_cond_new ();
+ waiter->ref_count = 0;
+ g_futex_address_list =
+ g_slist_prepend (g_futex_address_list, waiter);
+ }
+
+ waiter->ref_count++;
+ g_cond_wait (waiter->wait_queue, g_futex_mutex);
+
+ if (!--waiter->ref_count)
+ {
+ g_futex_address_list =
+ g_slist_remove (g_futex_address_list, waiter);
+ g_cond_free (waiter->wait_queue);
+ g_slice_free (WaitAddress, waiter);
+ }
+ }
+ g_mutex_unlock (g_futex_mutex);
+}
+
+static void
+g_futex_wake (const volatile gint *address)
+{
+ WaitAddress *waiter;
+
+ /* need to lock here for two reasons:
+ * 1) need to acquire/release lock to ensure waiter is not in
+ * the process of registering a wait
+ * 2) need to -stay- locked until the end to ensure a wake()
+ * in another thread doesn't cause 'waiter' to stop existing
+ */
+ g_mutex_lock (g_futex_mutex);
+ if ((waiter = g_futex_find_address (address)))
+ g_cond_signal (waiter->wait_queue);
+ g_mutex_unlock (g_futex_mutex);
+}
+#endif
+
+#define CONTENTION_CLASSES 11
+static volatile gint g_bit_lock_contended[CONTENTION_CLASSES];
+
+/**
+ * g_bit_lock:
+ * @address: a pointer to an integer
+ * @lock_bit: a bit value between 0 and 31
+ *
+ * Sets the indicated @lock_bit in @address. If the bit is already
+ * set, this call will block until g_bit_unlock() unsets the
+ * corresponding bit.
+ *
+ * Attempting to lock on two different bits within the same integer is
+ * not supported and will very probably cause deadlocks.
+ *
+ * The value of the bit that is set is (1u << @bit). If @bit is not
+ * between 0 and 31 then the result is undefined.
+ *
+ * This function accesses @address atomically. All other accesses to
+ * @address must be atomic in order for this function to work
+ * reliably.
+ **/
+void
+g_bit_lock (volatile gint *address,
+ gint lock_bit)
+{
+ guint v;
+
+ retry:
+ v = g_atomic_int_get (address);
+ if (v & (1u << lock_bit))
+ /* already locked */
+ {
+ guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
+
+ g_atomic_int_add (&g_bit_lock_contended[class], +1);
+ g_futex_wait (address, v);
+ g_atomic_int_add (&g_bit_lock_contended[class], -1);
+
+ goto retry;
+ }
+
+ if (!g_atomic_int_compare_and_exchange (address, v, v | (1u << lock_bit)))
+ goto retry;
+}
+
+/**
+ * g_bit_trylock:
+ * @address: a pointer to an integer
+ * @lock_bit: a bit value between 0 and 31
+ *
+ * Sets the indicated @lock_bit in @address, returning %TRUE if
+ * successful. If the bit is already set, returns %FALSE immediately.
+ *
+ * Attempting to lock on two different bits within the same integer is
+ * not supported.
+ *
+ * The value of the bit that is set is (1u << @bit). If @bit is not
+ * between 0 and 31 then the result is undefined.
+ *
+ * This function accesses @address atomically. All other accesses to
+ * @address must be atomic in order for this function to work
+ * reliably.
+ **/
+gboolean
+g_bit_trylock (volatile gint *address,
+ gint lock_bit)
+{
+ guint v;
+
+ retry:
+ v = g_atomic_int_get (address);
+ if (v & (1u << lock_bit))
+ /* already locked */
+ return FALSE;
+
+ if (!g_atomic_int_compare_and_exchange (address, v, v | (1u << lock_bit)))
+ goto retry;
+
+ return TRUE;
+}
+
+/**
+ * g_bit_unlock:
+ * @address: a pointer to an integer
+ * @lock_bit: a bit value between 0 and 31
+ *
+ * Clears the indicated @lock_bit in @address. If another thread is
+ * currently blocked in g_bit_lock() on this same bit then it will be
+ * woken up.
+ *
+ * This function accesses @address atomically. All other accesses to
+ * @address must be atomic in order for this function to work
+ * reliably.
+ **/
+void
+g_bit_unlock (volatile gint *address,
+ gint lock_bit)
+{
+ guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
+ guint v;
+
+ retry:
+ v = g_atomic_int_get (address);
+ if (!g_atomic_int_compare_and_exchange (address, v, v & ~(1u << lock_bit)))
+ goto retry;
+
+ if (g_atomic_int_get (&g_bit_lock_contended[class]))
+ g_futex_wake (address);
+}
+
+#define __G_BITLOCK_C__
+#include "galiasdef.c"
projects / platform / upstream / glib.git / commitdiff