Debian-bug: #595034

- in process.c (re-)start timer thread (after_exec) only in parent,
  as in child we know for sure that there is only one thread.
  The fix-up in child is performed slightly later in rb_thread_atfork().
  Also unify linux with rest of the systems.
  In 1.9 series the code is completely reworked.

- in signal.c use pthread_sigmask instead of sigprocmask,
  behaviour of sigprocmask is undefined in threaded programs, as stated in POSIX
  (http://www.opengroup.org/onlinepubs/9699919799/functions/pthread_sigmask.html).
  In 1.9 series the code already uses pthread_sigmask:

  Sat Apr 24 00:41:52 2010  Yusuke Endoh  <mame@tsg.ne.jp>

        * signal.c: use pthread_sigmask() instead of sigprocmask().
          sigprocmask() is unspecified behavior on multi-thread programs.
          [ruby-core:25217]

--- a/process.c
+++ b/process.c
@@ -1332,13 +1332,11 @@ rb_f_fork(obj)
 
     before_exec();
     pid = fork();
-    after_exec();
+    if (pid != 0)
+      after_exec();
 
     switch (pid) {
       case 0:
-#ifdef linux
-	after_exec();
-#endif
 	rb_thread_atfork();
 	if (rb_block_given_p()) {
 	    int status;
--- a/signal.c
+++ b/signal.c
@@ -545,7 +545,7 @@ sigsend_to_ruby_thread(int sig)
 
 # ifdef HAVE_SIGPROCMASK
     sigfillset(&mask);
-    sigprocmask(SIG_BLOCK, &mask, &old_mask);
+    pthread_sigmask(SIG_BLOCK, &mask, &old_mask);
 # else
     mask = sigblock(~0);
     sigsetmask(mask);
@@ -843,7 +843,7 @@ trap_ensure(arg)
 {
     /* enable interrupt */
 #ifdef HAVE_SIGPROCMASK
-    sigprocmask(SIG_SETMASK, &arg->mask, NULL);
+    pthread_sigmask(SIG_SETMASK, &arg->mask, NULL);
 #else
     sigsetmask(arg->mask);
 #endif
@@ -857,7 +857,7 @@ rb_trap_restore_mask()
 {
 #if USE_TRAP_MASK
 # ifdef HAVE_SIGPROCMASK
-    sigprocmask(SIG_SETMASK, &trap_last_mask, NULL);
+    pthread_sigmask(SIG_SETMASK, &trap_last_mask, NULL);
 # else
     sigsetmask(trap_last_mask);
 # endif
@@ -919,7 +919,7 @@ sig_trap(argc, argv)
     /* disable interrupt */
 # ifdef HAVE_SIGPROCMASK
     sigfillset(&arg.mask);
-    sigprocmask(SIG_BLOCK, &arg.mask, &arg.mask);
+    pthread_sigmask(SIG_BLOCK, &arg.mask, &arg.mask);
 # else
     arg.mask = sigblock(~0);
 # endif
@@ -1011,7 +1011,7 @@ init_sigchld(sig)
     /* disable interrupt */
 # ifdef HAVE_SIGPROCMASK
     sigfillset(&mask);
-    sigprocmask(SIG_BLOCK, &mask, &mask);
+    pthread_sigmask(SIG_BLOCK, &mask, &mask);
 # else
     mask = sigblock(~0);
 # endif
@@ -1027,7 +1027,7 @@ init_sigchld(sig)
 #if USE_TRAP_MASK
 #ifdef HAVE_SIGPROCMASK
     sigdelset(&mask, sig);
-    sigprocmask(SIG_SETMASK, &mask, NULL);
+    pthread_sigmask(SIG_SETMASK, &mask, NULL);
 #else
     mask &= ~sigmask(sig);
     sigsetmask(mask);