Index: lib/libthr/thread/thr_mutex.c
===================================================================
RCS file: /zoo/cvsup/FreeBSD-CVS/src/lib/libthr/thread/thr_mutex.c,v
retrieving revision 1.54
diff -u -r1.54 thr_mutex.c
--- lib/libthr/thread/thr_mutex.c	9 May 2007 08:39:33 -0000	1.54
+++ lib/libthr/thread/thr_mutex.c	28 Oct 2007 15:45:33 -0000
@@ -39,6 +39,8 @@
 #include <string.h>
 #include <sys/param.h>
 #include <sys/queue.h>
+#include <machine/cpu.h>
+#include <machine/cpufunc.h>
 #include <pthread.h>
 #include "un-namespace.h"
 
@@ -64,6 +66,10 @@
 #define MUTEX_ASSERT_NOT_OWNED(m)
 #endif
 
+/* For adaptive mutexes, how many times to spin doing trylock2
+   before entering the kernel to block */
+#define MUTEX_ADAPTIVE_SPINS	200
+
 /*
  * Prototypes
  */
@@ -355,6 +361,23 @@
 	} else if (m->m_owner == curthread) {
 		ret = mutex_self_lock(m, abstime);
 	} else {
+		/* For adaptive mutexes, spin for a bit in the expectation
+		   that if the application requests this mutex type then
+		   the lock is likely to be released quickly and it is
+		   faster than entering the kernel */
+		if (m->m_type == PTHREAD_MUTEX_ADAPTIVE_NP) {
+			int count = MUTEX_ADAPTIVE_SPINS;
+
+			while (count--) {
+				ret = _thr_umutex_trylock2(&m->m_lock, id);
+				if (ret == 0)
+					break;
+				cpu_spinwait();
+			}
+		}
+		if (ret == 0)
+			goto done;
+
 		if (abstime == NULL) {
 			ret = __thr_umutex_lock(&m->m_lock);
 		} else if (__predict_false(
@@ -372,6 +395,7 @@
 			if (ret == EINTR)
 				ret = ETIMEDOUT;
 		}
+done:
 		if (ret == 0) {
 			m->m_owner = curthread;
 			/* Add to the list of owned mutexes: */
@@ -501,6 +525,7 @@
 	switch (m->m_type) {
 	case PTHREAD_MUTEX_ERRORCHECK:
 	case PTHREAD_MUTEX_NORMAL:
+	case PTHREAD_MUTEX_ADAPTIVE_NP:
 		ret = EBUSY; 
 		break;
 
Index: lib/libkse/thread/thr_mutex.c
===================================================================
RCS file: /zoo/cvsup/FreeBSD-CVS/src/lib/libkse/thread/thr_mutex.c,v
retrieving revision 1.53
diff -u -r1.53 thr_mutex.c
--- lib/libkse/thread/thr_mutex.c	9 Oct 2007 13:42:28 -0000	1.53
+++ lib/libkse/thread/thr_mutex.c	27 Oct 2007 20:03:53 -0000
@@ -179,6 +179,7 @@
 			/* case PTHREAD_MUTEX_DEFAULT: */
 			case PTHREAD_MUTEX_ERRORCHECK:
 			case PTHREAD_MUTEX_NORMAL:
+			case PTHREAD_MUTEX_ADAPTIVE_NP:
 				/* Nothing to do here. */
 				break;
 
@@ -971,6 +972,7 @@
 	/* case PTHREAD_MUTEX_DEFAULT: */
 	case PTHREAD_MUTEX_ERRORCHECK:
 	case PTHREAD_MUTEX_NORMAL:
+	case PTHREAD_MUTEX_ADAPTIVE_NP:
 		ret = EBUSY; 
 		break;
 
@@ -1002,6 +1004,7 @@
 	switch (m->m_type) {
 	/* case PTHREAD_MUTEX_DEFAULT: */
 	case PTHREAD_MUTEX_ERRORCHECK:
+	case PTHREAD_MUTEX_ADAPTIVE_NP:
 		/*
 		 * POSIX specifies that mutexes should return EDEADLK if a
 		 * recursive lock is detected.
Index: include/pthread.h
===================================================================
RCS file: /zoo/cvsup/FreeBSD-CVS/src/include/pthread.h,v
retrieving revision 1.40
diff -u -r1.40 pthread.h
--- include/pthread.h	24 Oct 2005 05:53:54 -0000	1.40
+++ include/pthread.h	27 Oct 2007 18:32:34 -0000
@@ -98,6 +98,7 @@
  * Static initialization values. 
  */
 #define PTHREAD_MUTEX_INITIALIZER	NULL
+#define PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP	NULL
 #define PTHREAD_COND_INITIALIZER	NULL
 #define PTHREAD_RWLOCK_INITIALIZER	NULL
 
@@ -128,6 +129,7 @@
 	PTHREAD_MUTEX_ERRORCHECK	= 1,	/* Default POSIX mutex */
 	PTHREAD_MUTEX_RECURSIVE		= 2,	/* Recursive mutex */
 	PTHREAD_MUTEX_NORMAL		= 3,	/* No error checking */
+	PTHREAD_MUTEX_ADAPTIVE_NP	= 4,	/* Adaptive mutex, spins briefly before blocking on lock */
 	PTHREAD_MUTEX_TYPE_MAX
 };