hijack SIGCHLD handler for internal use

Use a global SIGCHLD handler to guard all callers of rb_waitpid.
To work safely with multi-threaded programs, we introduce a
VM-wide waitpid_lock to be acquired BEFORE fork/vfork spawns the
process.  This is to be combined with the new ruby_waitpid_locked
function used by mjit.c in a non-Ruby thread.

Ruby-level SIGCHLD handlers registered with Signal.trap(:CHLD)
continues to work as before and there should be no regressions
in any existing use cases.

Splitting the wait queues for PID > 0 and groups (PID <= 0)
ensures we favor PID > 0 callers.

The disabling of SIGCHLD in rb_f_system is longer necessary,
as we use deferred signal handling and no longer make ANY
blocking waitpid syscalls in other threads which could "beat"
the waitpid call made by rb_f_system.

We prevent SIGCHLD from firing in normal Ruby Threads and only
enable it in the timer-thread, to prevent spurious wakeups
from in test/-ext-/gvl/test_last_thread.rb with MJIT enabled.

I've tried to guard as much of the code for RUBY_SIGCHLD==0
using C "if" statements rather than CPP "#if" so to reduce
the likelyhood of portability problems as the compiler will
see more code.

We also work to suppress false-positives from
Process.wait(-1, Process::WNOHANG) to quiets warnings from
spec/ruby/core/process/wait2_spec.rb with MJIT enabled.

Lastly, we must implement rb_grantpt for ext/pty.  We need a
MJIT-compatible way of supporting grantpt(3) which may spawn
the `pt_chown' binary and call waitpid(2) on it.

[ruby-core:87605] [Ruby trunk Bug#14867]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63758 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 25 insertions, 0 deletions

diff --git a/thread_pthread.c b/thread_pthread.c
index 1a1a6fc0c6..6ac7728ad9 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -1479,6 +1479,13 @@ static void *
 thread_timer(void *p)
 {
     rb_global_vm_lock_t *gvl = (rb_global_vm_lock_t *)p;
+#ifdef HAVE_PTHREAD_SIGMASK /* mainly to enable SIGCHLD */
+    {
+        sigset_t mask;
+        sigemptyset(&mask);
+        pthread_sigmask(SIG_SETMASK, &mask, NULL);
+    }
+#endif
 
     if (TT_DEBUG) WRITE_CONST(2, "start timer thread\n");
 
@@ -1764,4 +1771,22 @@ rb_thread_create_mjit_thread(void (*child_hook)(void), void (*worker_func)(void)
     return ret;
 }
 
+#define USE_NATIVE_SLEEP_COND (1)
+
+#if USE_NATIVE_SLEEP_COND
+rb_nativethread_cond_t *
+rb_sleep_cond_get(const rb_execution_context_t *ec)
+{
+    rb_thread_t *th = rb_ec_thread_ptr(ec);
+
+    return &th->native_thread_data.sleep_cond;
+}
+
+void
+rb_sleep_cond_put(rb_nativethread_cond_t *cond)
+{
+    /* no-op */
+}
+#endif /* USE_NATIVE_SLEEP_COND */
+
 #endif /* THREAD_SYSTEM_DEPENDENT_IMPLEMENTATION */