--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,22 @@
+2010-09-22  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* lib/pthread.in.h: Add split double-inclusion guard, and include
+	system <pthread.h> if there is one.  Use @@-style as in other
+	.in.h files.  Define PTHREAD_COND_INITIALIZER etc. only if system
+	pthread.h doesn't.
+	(pthread_mutexattr_destroy, pthread_mutexattr_init):
+	(pthread_mutexattr_settype, pthread_mutex_trylock):
+	New static inline functions, if there's no system <pthread.h>.
+	(pthread_spinlock_t, pthread_spin_init, pthread_spin_destroy):
+	(pthread_spin_lock, pthread_spin_trylock, pthread_spin_unlock):
+	Approximate with mutexes if the system lacks spinlocks, as in
+	MacOS.
+	* m4/pthread.m4 (gl_PTHREAD_CHECK): Require gl_PTHREAD_DEFAULTS.
+	Add gl_CHECK_NEXT_HEADERS for pthread.h, and support the usual
+	@@-style.  Check for spinlocks separately.
+	(gl_PTHREAD_DEFAULTS): New macro.
+	* modules/pthread: Redo to use a more typical style for in.h files.
+
 2010-09-21  Eric Blake  <eblake@redhat.com>
 
 	net_if: enhance tests

--- a/lib/pthread.in.h
+++ b/lib/pthread.in.h
@@ -19,6 +19,17 @@
 /* Written by Paul Eggert and Glen Lenker.  */
 
 #ifndef _GL_PTHREAD_H_
+
+#if __GNUC__ >= 3
+@PRAGMA_SYSTEM_HEADER@
+#endif
+
+/* The include_next requires a split double-inclusion guard.  */
+#if @HAVE_PTHREAD_H@
+# @INCLUDE_NEXT@ @NEXT_PTHREAD_H@
+#endif
+
+#ifndef _GL_PTHREAD_H_
 #define _GL_PTHREAD_H_
 
 #include <errno.h>
@@ -27,7 +38,7 @@
 #include <sys/types.h>
 #include <time.h>
 
-#ifndef HAVE_PTHREAD_T
+#if ! @HAVE_PTHREAD_T@
  typedef int pthread_t;
  typedef int pthread_attr_t;
  typedef int pthread_barrier_t;
@@ -40,9 +51,9 @@
  typedef int pthread_once_t;
  typedef int pthread_rwlock_t;
  typedef int pthread_rwlockattr_t;
- typedef int pthread_spinlock_t;
 #endif
 
+#ifndef PTHREAD_COND_INITIALIZER
 #define PTHREAD_COND_INITIALIZER { 0 }
 #define PTHREAD_MUTEX_INITIALIZER { 0 }
 #define PTHREAD_ONCE_INIT { 0 }
@@ -81,6 +92,9 @@
 
 #define PTHREAD_SCOPE_SYSTEM 0
 #define PTHREAD_SCOPE_PROCESS 1
+#endif
+
+#if ! @HAVE_PTHREAD_T@
 
 /* Provide substitutes for the thread functions that should work
    adequately on a single-threaded implementation, where
@@ -147,6 +161,24 @@
 }
 
 static inline int
+pthread_mutexattr_destroy (pthread_mutexattr_t *attr)
+{
+  return 0;
+}
+
+static inline int
+pthread_mutexattr_init (pthread_mutexattr_t *attr)
+{
+  return 0;
+}
+
+static inline int
+pthread_mutexattr_settype (pthread_mutexattr_t *attr, int attr_type)
+{
+  return 0;
+}
+
+static inline int
 pthread_mutex_destroy (pthread_mutex_t *mutex)
 {
   /* MUTEX is never seriously used.  */
@@ -170,6 +202,12 @@
 }
 
 static inline int
+pthread_mutex_trylock (pthread_mutex_t *mutex)
+{
+  return pthread_mutex_lock (mutex);
+}
+
+static inline int
 pthread_mutex_unlock (pthread_mutex_t *mutex)
 {
   /* There is only one thread, so it always unlocks successfully.
@@ -178,40 +216,44 @@
   return 0;
 }
 
+#endif
+
+#if ! @HAVE_PTHREAD_SPINLOCK_T@
+
+/* Approximate spinlocks with mutexes.  */
+
+typedef pthread_mutex_t pthread_spinlock_t;
+
 static inline int
 pthread_spin_init (pthread_spinlock_t *lock, int pshared)
 {
-  /* LOCK is never seriously used.  */
-  return 0;
+  return pthread_mutex_init (lock, NULL);
 }
 
 static inline int
 pthread_spin_destroy (pthread_spinlock_t *lock)
 {
-  /* LOCK is never seriously used.  */
-  return 0;
+  return pthread_mutex_destroy (lock);
 }
 
 static inline int
 pthread_spin_lock (pthread_spinlock_t *lock)
 {
-  /* Only one thread, so it always gets the lock.  */
-  return 0;
+  return pthread_mutex_lock (lock);
 }
 
 static inline int
 pthread_spin_trylock (pthread_spinlock_t *lock)
 {
-  /* Only one thread, so it always gets the lock.  Assume that a
-     thread never tries a lock that it already holds.  */
-  return 0;
+  return pthread_mutex_trylock (lock);
 }
 
 static inline int
 pthread_spin_unlock (pthread_spinlock_t *lock)
 {
-  /* Only one thread, so spin locks are no-ops.  */
-  return 0;
+  return pthread_mutex_unlock (lock);
 }
+#endif
 
 #endif /* _GL_PTHREAD_H_ */
+#endif /* _GL_PTHREAD_H_ */

--- a/m4/pthread.m4
+++ b/m4/pthread.m4
@@ -5,25 +5,54 @@
 dnl with or without modifications, as long as this notice is preserved.
 
 AC_DEFUN([gl_PTHREAD_CHECK],
-  [AC_CHECK_HEADERS_ONCE([pthread.h])
+[
+   AC_REQUIRE([gl_PTHREAD_DEFAULTS])
+   AC_CHECK_HEADERS_ONCE([pthread.h])
+   gl_CHECK_NEXT_HEADERS([pthread.h])
+   if test $ac_cv_header_pthread_h = yes; then
+     HAVE_PTHREAD_H=1
+   else
+     HAVE_PTHREAD_H=0
+   fi
+
+   AC_CHECK_TYPES([pthread_t, pthread_spinlock_t], [], [],
+     [AC_INCLUDES_DEFAULT[
+      #if HAVE_PTHREAD_H
+       #include <pthread.h>
+      #endif]])
+   if test $ac_cv_type_pthread_t != yes; then
+     HAVE_PTHREAD_T=0
+   fi
+   if test $ac_cv_type_pthread_spinlock_t != yes; then
+     HAVE_PTHREAD_SPINLOCK_T=0
+   fi
+
+   if test $ac_cv_header_pthread_h != yes ||
+      test $ac_cv_type_pthread_t != yes ||
+      test $ac_cv_type_pthread_spinlock_t != yes; then
+     PTHREAD_H='pthread.h'
+   fi
 
    LIB_PTHREAD=
-   PTHREAD_H=
-   if test "$ac_cv_header_pthread_h" = yes; then
+   if test $ac_cv_header_pthread_h = yes; then
      gl_saved_libs=$LIBS
      AC_SEARCH_LIBS([pthread_create], [pthread],
        [if test "$ac_cv_search_pthread_create" != "none required"; then
           LIB_PTHREAD="$ac_cv_search_pthread_create"
         fi])
      LIBS="$gl_saved_libs"
-   else
-     AC_CHECK_TYPES([pthread_t])
-     PTHREAD_H='pthread.h'
    fi
-
    AC_SUBST([LIB_PTHREAD])
-   AC_SUBST([PTHREAD_H])
 
    AC_REQUIRE([AC_C_INLINE])
    AC_REQUIRE([AC_C_RESTRICT])
 ])
+
+AC_DEFUN([gl_PTHREAD_DEFAULTS],
+[
+  dnl Assume proper GNU behavior unless another module says otherwise.
+  HAVE_PTHREAD_H=1;              AC_SUBST([HAVE_PTHREAD_H])
+  HAVE_PTHREAD_T=1;              AC_SUBST([HAVE_PTHREAD_T])
+  HAVE_PTHREAD_SPINLOCK_T=1;     AC_SUBST([HAVE_PTHREAD_SPINLOCK_T])
+  PTHREAD_H='';                  AC_SUBST([PTHREAD_H])
+])

--- a/modules/pthread
+++ b/modules/pthread
@@ -18,9 +18,18 @@
 # We need the following in order to create <pthread.h> when the system
 # doesn't have one that works with the given compiler.
 pthread.h: pthread.in.h
-	$(AM_V_GEN)ln -f $(srcdir)/pthread.in.h $@ \
-          || cp $(srcdir)/pthread.in.h $@
-MOSTLYCLEANFILES += pthread.h
+	$(AM_V_GEN)rm -f $@-t $@ && \
+	{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */'; \
+	  sed -e 's|@''HAVE_PTHREAD_H''@|$(HAVE_PTHREAD_H)|g' \
+	      -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
+	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
+	      -e 's|@''NEXT_PTHREAD_H''@|$(NEXT_PTHREAD_H)|g' \
+	      -e 's|@''HAVE_PTHREAD_T''@|$(HAVE_PTHREAD_T)|g' \
+	      -e 's|@''HAVE_PTHREAD_SPINLOCK_T''@|$(HAVE_PTHREAD_SPINLOCK_T)|g' \
+	      < $(srcdir)/pthread.in.h; \
+	} > $@-t && \
+	mv $@-t $@
+MOSTLYCLEANFILES += pthread.h pthread.h-t
 
 Include:
 <pthread.h>