From 76cd6b5114fc41d5dd782de2fec94b2644745158 Mon Sep 17 00:00:00 2001
From: Sears Russell <sears@cs.berkeley.edu>
Date: Thu, 8 Mar 2007 07:36:02 +0000
Subject: [PATCH] Added tryreadlock() and trywritelock().

---
 libdfa/rw.h     |  2 ++
 src/libdfa/rw.c | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/libdfa/rw.h b/libdfa/rw.h
index 41d473f..ac2ceb3 100644
--- a/libdfa/rw.h
+++ b/libdfa/rw.h
@@ -32,7 +32,9 @@ typedef struct {
 
 rwl *initlock (void);
 void readlock (rwl *lock, int d);
+int tryreadlock(rwl *lock, int d);
 void writelock (rwl *lock, int d);
+int trywritelock(rwl *lock, int d);
 void downgradelock(rwl * lock);
 void unlock(rwl * lock);
 /** @deprecated in favor of unlock() */
diff --git a/src/libdfa/rw.c b/src/libdfa/rw.c
index f98d8b6..448947c 100644
--- a/src/libdfa/rw.c
+++ b/src/libdfa/rw.c
@@ -56,6 +56,18 @@ void readlock (rwl *lock, int d)
   
   return;
 }
+int tryreadlock (rwl *lock, int d)
+{
+  pthread_mutex_lock (lock->mut);
+  if (lock->writers || lock->waiting) {
+    pthread_mutex_unlock (lock->mut);
+    return 0;
+  }
+  lock->readers++;
+  pthread_mutex_unlock (lock->mut);
+  return 1;
+}
+
 
 void writelock (rwl *lock, int d)
 {
@@ -78,6 +90,19 @@ void writelock (rwl *lock, int d)
   return;
 }
 
+int trywritelock(rwl *lock, int d) {
+  /*  printf("\nwritelock %d\n", d);
+      fflush(NULL); */
+  pthread_mutex_lock (lock->mut);
+  if (lock->readers || lock->writers) {
+    pthread_mutex_unlock(lock->mut);
+    return 0;
+  }
+  lock->writers++;
+  pthread_mutex_unlock (lock->mut);
+  return 1;
+} 
+
 void downgradelock(rwl * lock) {
   pthread_mutex_lock(lock->mut);
   assert(lock->writers);