my_pthread.h, configure.in:

  In HP-UX-10.20, but not in HP-UX-11.0, the return value of pthread_mutex_trylock is inverted

configure.in

@@ -849,8 +849,8 @@ case $SYSTEM_TYPE in
     ;;
   *hpux10.20*)
     echo "Enabling workarounds for hpux 10.20"
-    CFLAGS="$CFLAGS -DHAVE_BROKEN_SNPRINTF -DSIGNALS_DONT_BREAK_READ -DDO_NOT_REMOVE_THREAD_WRAPPERS -DHPUX -DSIGNAL_WITH_VIO_CLOSE -DHAVE_BROKEN_PTHREAD_COND_TIMEDWAIT"
-    CXXFLAGS="$CXXFLAGS -DHAVE_BROKEN_SNPRINTF -D_INCLUDE_LONGLONG -DSIGNALS_DONT_BREAK_READ -DDO_NOT_REMOVE_THREAD_WRAPPERS -DHPUX -DSIGNAL_WITH_VIO_CLOSE -DHAVE_BROKEN_PTHREAD_COND_TIMEDWAIT"
+    CFLAGS="$CFLAGS -DHAVE_BROKEN_SNPRINTF -DSIGNALS_DONT_BREAK_READ -DDO_NOT_REMOVE_THREAD_WRAPPERS -DHPUX -DSIGNAL_WITH_VIO_CLOSE -DHAVE_BROKEN_PTHREAD_COND_TIMEDWAIT -DPTHREAD_MUTEX_TRYLOCK_INVERTED_RET_VAL"
+    CXXFLAGS="$CXXFLAGS -DHAVE_BROKEN_SNPRINTF -D_INCLUDE_LONGLONG -DSIGNALS_DONT_BREAK_READ -DDO_NOT_REMOVE_THREAD_WRAPPERS -DHPUX -DSIGNAL_WITH_VIO_CLOSE -DHAVE_BROKEN_PTHREAD_COND_TIMEDWAIT -DPTHREAD_MUTEX_TRYLOCK_INVERTED_RET_VAL"
     if test "$with_named_thread" = "no"
     then 
       echo "Using --with-named-thread=-lpthread"

include/my_pthread.h

@@ -464,7 +464,14 @@ int safe_cond_timedwait(pthread_cond_t *cond, safe_mutex_t *mp,
 #define pthread_mutex_destroy(A) safe_mutex_destroy((A),__FILE__,__LINE__)
 #define pthread_cond_wait(A,B) safe_cond_wait((A),(B),__FILE__,__LINE__)
 #define pthread_cond_timedwait(A,B,C) safe_cond_timedwait((A),(B),(C),__FILE__,__LINE__)
+#ifdef PTHREAD_MUTEX_TRYLOCK_INVERTED_RET_VAL
+  /* In HP-UX-10.20 and other old Posix 1003.4a Draft 4 implementations
+     pthread_mutex_trylock returns 1 on success, not 0 like
+     pthread_mutex_lock */
+#define pthread_mutex_trylock(A) (1 - pthread_mutex_lock(A))
+#else
 #define pthread_mutex_trylock(A) pthread_mutex_lock(A)
+#endif
 #define pthread_mutex_t safe_mutex_t
 #endif /* SAFE_MUTEX */