Move process write part (atfork) to OS layer

Migrates pthread_atfork(3) registration onto the existing os/process.h
dispatcher.

include/jemalloc/internal/os/posix/process.h

@@ -14,4 +14,31 @@ os_process_id(void) {
 	return (int)getpid();
 }
 
+/*
+ * Shared by every POSIX platform: the four predicates below reproduce, in one
+ * place, exactly which platforms actually get pthread_atfork() registered.
+ *   - JEMALLOC_HAVE_PTHREAD_ATFORK: the function exists.
+ *   - !JEMALLOC_MUTEX_INIT_CB: on FreeBSD-libthr, _pthread_mutex_init_calloc_cb
+ *     makes libthr's own _malloc_prefork/_malloc_postfork drive the fork
+ *     dance instead.  Registering here would be redundant.
+ *   - !JEMALLOC_ZONE: on Darwin, malloc-zone fork callbacks subsume
+ *     pthread_atfork.
+ *   - !__native_client__: Native Client's sandbox doesn't support fork() at
+ *     all, and pthread_atfork() risked being an unresolved symbol in some
+ *     NaCl toolchains.  Registering it is both pointless and unsafe there.
+ */
+JEMALLOC_ALWAYS_INLINE bool
+os_process_register_atfork(void (*prepare)(void), void (*parent)(void),
+    void (*child)(void)) {
+#if defined(JEMALLOC_HAVE_PTHREAD_ATFORK) && !defined(JEMALLOC_MUTEX_INIT_CB) \
+    && !defined(JEMALLOC_ZONE) && !defined(__native_client__)
+	return pthread_atfork(prepare, parent, child) != 0;
+#else
+	(void)prepare;
+	(void)parent;
+	(void)child;
+	return false;
+#endif
+}
+
 #endif /* JEMALLOC_INTERNAL_OS_POSIX_PROCESS_H */

include/jemalloc/internal/os/process.h

@@ -11,6 +11,12 @@
 
 /* Functions required for implementation in each backend. */
 JEMALLOC_ALWAYS_INLINE int os_process_id(void);
+/*
+ * Install fork handlers, returning true on failure.  A no-op returning false
+ * where fork handler registration doesn't apply.
+ */
+JEMALLOC_ALWAYS_INLINE bool os_process_register_atfork(
+    void (*prepare)(void), void (*parent)(void), void (*child)(void));
 
 #if defined(_WIN32)
 #  include "jemalloc/internal/os/windows/process.h"

include/jemalloc/internal/os/windows/process.h

@@ -12,4 +12,14 @@ os_process_id(void) {
 	return (int)GetCurrentProcessId();
 }
 
+/* Windows has no fork(2)/pthread_atfork; always a no-op. */
+JEMALLOC_ALWAYS_INLINE bool
+os_process_register_atfork(void (*prepare)(void), void (*parent)(void),
+    void (*child)(void)) {
+	(void)prepare;
+	(void)parent;
+	(void)child;
+	return false;
+}
+
 #endif /* JEMALLOC_INTERNAL_OS_WINDOWS_PROCESS_H */

src/jemalloc_init.c

@@ -347,13 +347,18 @@ malloc_init_hard_recursible(void) {
 		}
 	}
 
-#if (defined(JEMALLOC_HAVE_PTHREAD_ATFORK) && !defined(JEMALLOC_MUTEX_INIT_CB) \
+#ifndef JEMALLOC_MUTEX_INIT_CB
-    && !defined(JEMALLOC_ZONE) && !defined(_WIN32)                             \
+	/*
-    && !defined(__native_client__))
+	 * jemalloc_fork.c names these jemalloc_prefork()/jemalloc_postfork_
-	/* LinuxThreads' pthread_atfork() allocates. */
+	 * parent() only when !JEMALLOC_MUTEX_INIT_CB; under it they're exported
-	if (pthread_atfork(jemalloc_prefork, jemalloc_postfork_parent,
+	 * as _malloc_prefork()/_malloc_postfork() instead (FreeBSD-libthr calls
-	        jemalloc_postfork_child)
+	 * those directly, bypassing pthread_atfork() registration entirely --
-	    != 0) {
+	 * see os_process_register_atfork()'s own !JEMALLOC_MUTEX_INIT_CB check).
+	 * Referencing the former names here unconditionally would be a link
+	 * error under JEMALLOC_MUTEX_INIT_CB, since they wouldn't exist.
+	 */
+	if (os_process_register_atfork(jemalloc_prefork,
+	        jemalloc_postfork_parent, jemalloc_postfork_child)) {
 		malloc_write("<jemalloc>: Error in pthread_atfork()\n");
 		if (opt_abort) {
 			abort();