Normalize background thread configuration.

Also fix a compilation error #ifndef JEMALLOC_PTHREAD_CREATE_WRAPPER.

configure.ac

@@ -1452,6 +1452,7 @@ if test "x$abi" != "xpecoff" ; then
                [AC_SEARCH_LIBS([pthread_create], , ,
                                AC_MSG_ERROR([libpthread is missing]))])
   wrap_syms="${wrap_syms} pthread_create"
+  have_pthread="1"
   dnl Check if we have dlsym support.
   have_dlsym="1"
   AC_CHECK_HEADERS([dlfcn.h],
@@ -1933,6 +1934,15 @@ if test "x${enable_zone_allocator}" = "x1" ; then
   AC_DEFINE([JEMALLOC_ZONE], [ ])
 fi
 
+dnl ============================================================================
+dnl Enable background threads if possible.
+
+if test "x${have_pthread}" = "x1" -a "x${have_dlsym}" = "x1" \
+    -a "x${je_cv_os_unfair_lock}" != "xyes" \
+    -a "x${je_cv_osspin}" != "xyes" ; then
+  AC_DEFINE([JEMALLOC_BACKGROUND_THREAD])
+fi
+
 dnl ============================================================================
 dnl Check for glibc malloc hooks
 

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -316,6 +316,11 @@
 /* GNU specific sched_setaffinity support */
 #undef JEMALLOC_HAVE_SCHED_SETAFFINITY
 
+/*
+ * If defined, all the features necessary for background threads are present.
+ */
+#undef JEMALLOC_BACKGROUND_THREAD
+
 /*
  * If defined, jemalloc symbols are not exported (doesn't work when
  * JEMALLOC_PREFIX is not defined).

include/jemalloc/internal/jemalloc_preamble.h.in

@@ -168,12 +168,6 @@ static const bool force_ivsalloc =
     false
 #endif
     ;
-
-#if (defined(JEMALLOC_HAVE_PTHREAD) && defined(JEMALLOC_HAVE_DLSYM)	\
-    && !defined(JEMALLOC_OSSPIN) && !defined(JEMALLOC_OS_UNFAIR_LOCK))
-/* Currently background thread supports pthread only. */
-#define JEMALLOC_BACKGROUND_THREAD
-#endif
 static const bool have_background_thread =
 #ifdef JEMALLOC_BACKGROUND_THREAD
     true

src/background_thread.c

@@ -635,7 +635,9 @@ background_thread_stats_read(tsdn_t *tsdn, background_thread_stats_t *stats) {
 void
 background_thread_ctl_init(tsdn_t *tsdn) {
 	malloc_mutex_assert_not_owner(tsdn, &background_thread_lock);
+#ifdef JEMALLOC_PTHREAD_CREATE_WRAPPER
 	pthread_once(&once_control, pthread_create_wrapper_once);
+#endif
 }
 
 #endif /* defined(JEMALLOC_BACKGROUND_THREAD) */