Always use adaptive mutexes on Linux

When adaptive mutexes are available (with glibc), always use them.
Remove the autoconf switch and also fix the static initializer.

configure.ac

@@ -562,30 +562,6 @@ AC_ARG_WITH([locktype],
 			    (adaptive or standard)]),
 	    [], [with_locktype="adaptive"])
 
-AS_CASE([$with_locktype],
-	[adaptive],[
-	  AC_MSG_CHECKING([for PTHREAD_MUTEX_ADAPTIVE_NP])
-	  AC_COMPILE_IFELSE(
-	    [AC_LANG_PROGRAM(
-	       [[
-		 #ifndef _GNU_SOURCE
-		 #define _GNU_SOURCE
-		 #endif
-		 #include <pthread.h>
-	       ]],
-	       [[
-		 return (PTHREAD_MUTEX_ADAPTIVE_NP);
-	       ]]
-	     )],
-	    [AC_MSG_RESULT([using adaptive lock type])
-	     AC_DEFINE([HAVE_PTHREAD_MUTEX_ADAPTIVE_NP], 1,
-		       [Support for PTHREAD_MUTEX_ADAPTIVE_NP]) ],
-	    [AC_MSG_RESULT([using standard lock type])]
-	  )],
-	[standard],[AC_MSG_RESULT([using standard lock type])],
-	[AC_MSG_ERROR([You must specify "adaptive" or "standard" for --with-locktype.])]
-       )
-
 AC_CHECK_HEADERS([sched.h])
 
 AC_SEARCH_LIBS([sched_yield],[rt])

lib/isc/include/isc/mutex.h

@@ -23,7 +23,11 @@
 #include <isc/result.h> /* for ISC_R_ codes */
 #include <isc/util.h>
 
+#if defined(PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP)
+#define ISC_MUTEX_INITIALIZER PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
+#else
 #define ISC_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+#endif
 
 ISC_LANG_BEGINDECLS
 

lib/isc/mutex.c

@@ -33,7 +33,7 @@ static isc_once_t init_once = ISC_ONCE_INIT;
 static void
 mutex_initialize(void) {
 	RUNTIME_CHECK(pthread_mutexattr_init(&isc__mutex_init_attr) == 0);
-#ifdef HAVE_PTHREAD_MUTEX_ADAPTIVE_NP
+#if defined(PTHREAD_MUTEX_ADAPTIVE_NP)
 	RUNTIME_CHECK(pthread_mutexattr_settype(&isc__mutex_init_attr,
 						PTHREAD_MUTEX_ADAPTIVE_NP) ==
 		      0);