X-Git-Url: http://ftp.carnet.hr/carnet-debian/scm?a=blobdiff_plain;f=apc_futex.c;fp=apc_futex.c;h=89069ff9cd131a26a53faeea1473f3e495abe353;hb=3682e0a7a26931aabca2b6e54eb08efd7dc0430b;hp=0000000000000000000000000000000000000000;hpb=575ce08215526bb71a967d69d601e77e1afbcd11;p=php5-apc.git

diff --git a/apc_futex.c b/apc_futex.c
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+/*
+  +----------------------------------------------------------------------+
+  | APC                                                                  |
+  +----------------------------------------------------------------------+
+  | Copyright (c) 2006 The PHP Group                                     |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | http://www.php.net/license/3_01.txt                                  |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | license@php.net so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Authors: Brian Shire <shire@php.net>                                 |
+  +----------------------------------------------------------------------+
+
+ */
+
+/* $Id: apc_futex.c,v 3.2 2006/10/12 08:23:16 shire Exp $ */
+
+/***************************************************************************
+* Futex (Fast Userspace Mutex) support for APC
+* 
+* Futex support provides user space locking with system calls only
+* for the contended cases.  Some required reading for this functionality is:
+*
+* 'Fuss, Futexes and Furwocks: Fast Userlevel Locking in Linux' 
+*  by Hubertus Franke, Rusty Russell, and Matthew Kirkwood
+*   http://www.realitydiluted.com/nptl-uclibc/docs/futex.pdf
+*
+* 'Futexes are Tricky' by Ulrich Drepper 
+*    http://people.redhat.com/drepper/futex.pdf
+*
+* 
+* This implementation is optimized and designed for the i386 and x86_64 
+* architectures.  Other architectures may require additional design 
+* to efficiently and safely implement this functionality. 
+*
+* Lock values are:
+* 0 = Unlocked
+* 1 = Locked without any waiting processes
+* 2 = Locked with an unknown number of waiting processes
+*
+***************************************************************************/
+
+#include "apc.h"
+#include "apc_futex.h"
+
+#ifdef APC_FUTEX_LOCKS
+
+
+inline int apc_futex_create()
+{
+    return 0;
+}
+
+inline void apc_futex_destroy(volatile int* lock)
+{
+    return;
+}
+
+void apc_futex_lock(volatile int* lock)
+{
+    int c;
+  
+    /*  Attempt to obtain a lock if not currently locked.  If the previous
+     *  value was not 0 then we did not obtain the lock, and must wait.
+     *  If the previous value was 1 (has no waiting processes) then we
+     *  set the lock to 2 before blocking on the futex wait operation.  
+     *  This implementation suffers from the possible difficulty of 
+     *  efficently implementing the atomic xchg operation on some
+     *  architectures, and could also cause unecessary wake operations by
+     *  setting the lock to 2 when there are no additional waiters.
+     */ 
+    if((c = apc_cmpxchg(lock, 0, 1)) != 0) {
+        if(c != 2) {
+            c = apc_xchg(lock, 2);
+        }
+        while(c != 0) {
+            apc_futex_wait(lock, 2);
+            c = apc_xchg(lock, 2);
+        }
+    }
+    
+}
+
+/* non-blocking lock returns 1 when the lock has been obtained, 0 if it would block */
+inline zend_bool apc_futex_nonblocking_lock(volatile int* lock)
+{
+    return apc_cmpxchg(lock, 0, 1) == 0;
+}
+
+
+inline void apc_futex_unlock(volatile int* lock)
+{
+    /* set the lock to 0, if it's previous values was not 1 (no waiters)
+     * then perform a wake operation on one process letting it know the lock 
+     * is available.  This is an optimization to save wake calls if there
+     * are no waiting processes for the lock 
+     */
+    if(apc_xchg(lock,0) != 1) {
+        apc_futex_wake(lock, 1);
+    }
+}
+
+#endif
+
+/*
+ * Local variables:
+ * tab-width: 4
+ * c-basic-offset: 4
+ * End:
+ * vim600: expandtab sw=4 ts=4 sts=4 fdm=marker
+ * vim<600: expandtab sw=4 ts=4 sts=4
+ */