rwlocks writer preference patch (take 2)

[Momchil Velikov <velco at fadata dot bg>]

Hi,

Here's the second version of the patch, as suggested by Kaz.

Regards,
-velco
--- rwlock.c.orig	Thu Nov  9 15:19:19 2000
+++ rwlock.c	Fri Nov 10 14:55:55 2000
@@ -234,11 +234,11 @@
   have_lock_already = rwlock_have_already(&self, rwlock,
       &existing, &out_of_mem);
 
-  for (;;)
-    {
       if (self == NULL)
 	self = thread_self ();
 
+  for (;;)
+    {
       __pthread_lock (&rwlock->__rw_lock, self);
 
       if (rwlock_can_rdlock(rwlock, have_lock_already))
@@ -310,9 +310,9 @@
 {
   pthread_descr self = thread_self ();
 
+  __pthread_lock (&rwlock->__rw_lock, self);
   while(1)
     {
-      __pthread_lock (&rwlock->__rw_lock, self);
       if (rwlock->__rw_readers == 0 && rwlock->__rw_writer == NULL)
 	{
 	  rwlock->__rw_writer = self;
@@ -324,6 +324,14 @@
       enqueue (&rwlock->__rw_write_waiting, self);
       __pthread_unlock (&rwlock->__rw_lock);
       suspend (self); /* This is not a cancellation point */
+      __pthread_lock (&rwlock->__rw_lock, self);
+
+      /* Check if someone handed us ownership of the lock */
+      if (rwlock->__rw_writer == self) 
+        {
+          __pthread_unlock (&rwlock->__rw_lock);
+	  return 0;
+        }
     }
 }
 
@@ -362,7 +370,8 @@
 	}
       rwlock->__rw_writer = NULL;
 
-      if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
+      if ((rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
+	   && !queue_is_empty(&rwlock->__rw_read_waiting))
 	  || (th = dequeue (&rwlock->__rw_write_waiting)) == NULL)
 	{
 	  /* Restart all waiting readers.  */
@@ -375,6 +384,7 @@
       else
 	{
 	  /* Restart one waiting writer.  */
+	  rwlock->__rw_writer = th;
 	  __pthread_unlock (&rwlock->__rw_lock);
 	  restart (th);
 	}
@@ -390,8 +400,11 @@
 
       --rwlock->__rw_readers;
       if (rwlock->__rw_readers == 0)
+	{
 	/* Restart one waiting writer, if any.  */
 	th = dequeue (&rwlock->__rw_write_waiting);
+	  rwlock->__rw_writer = th;
+	}
       else
 	th = NULL;
 
@@ -430,8 +443,8 @@
 int
 pthread_rwlockattr_init (pthread_rwlockattr_t *attr)
 {
-  attr->__lockkind = 0;
-  attr->__pshared = 0;
+  attr->__lockkind = PTHREAD_RWLOCK_DEFAULT_NP;
+  attr->__pshared = PTHREAD_PROCESS_PRIVATE;
 
   return 0;
 }
@@ -477,6 +490,7 @@
 {
   if (pref != PTHREAD_RWLOCK_PREFER_READER_NP
       && pref != PTHREAD_RWLOCK_PREFER_WRITER_NP
+      && pref != PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
       && pref != PTHREAD_RWLOCK_DEFAULT_NP)
     return EINVAL;