patch-2.4.20 linux-2.4.20/lib/rwsem-spinlock.c

• Lines: 67
• Date: Thu Nov 28 15:53:15 2002
• Orig file: linux-2.4.19/lib/rwsem-spinlock.c
• Orig date: Wed Apr 25 13:31:03 2001

diff -urN linux-2.4.19/lib/rwsem-spinlock.c linux-2.4.20/lib/rwsem-spinlock.c
@@ -4,6 +4,8 @@
  * Copyright (c) 2001   David Howells (dhowells@redhat.com).
  * - Derived partially from idea by Andrea Arcangeli <andrea@suse.de>
  * - Derived also from comments by Linus
+ *
+ * Trylock by Brian Watson (Brian.J.Watson@compaq.com).
  */
 #include <linux/rwsem.h>
 #include <linux/sched.h>
@@ -149,6 +151,28 @@
 }
 
 /*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int __down_read_trylock(struct rw_semaphore *sem)
+{
+	int ret = 0;
+	rwsemtrace(sem,"Entering __down_read_trylock");
+
+	spin_lock(&sem->wait_lock);
+
+	if (sem->activity>=0 && list_empty(&sem->wait_list)) {
+		/* granted */
+		sem->activity++;
+		ret = 1;
+	}
+
+	spin_unlock(&sem->wait_lock);
+
+	rwsemtrace(sem,"Leaving __down_read_trylock");
+	return ret;
+}
+
+/*
  * get a write lock on the semaphore
  * - note that we increment the waiting count anyway to indicate an exclusive lock
  */
@@ -195,6 +219,28 @@
 }
 
 /*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+int __down_write_trylock(struct rw_semaphore *sem)
+{
+	int ret = 0;
+	rwsemtrace(sem,"Entering __down_write_trylock");
+
+	spin_lock(&sem->wait_lock);
+
+	if (sem->activity==0 && list_empty(&sem->wait_list)) {
+		/* granted */
+		sem->activity = -1;
+		ret = 1;
+	}
+
+	spin_unlock(&sem->wait_lock);
+
+	rwsemtrace(sem,"Leaving __down_write_trylock");
+	return ret;
+}
+
+/*
  * release a read lock on the semaphore
  */
 void __up_read(struct rw_semaphore *sem)