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, 34 insertions, 0 deletions

diff --git a/thread.c b/thread.c
index 5a5e32379d..c58d3e0b9d 100644
--- a/thread.c
+++ b/thread.c
@@ -413,6 +413,10 @@ rb_vm_gvl_destroy(rb_vm_t *vm)
     gvl_release(vm);
     gvl_destroy(vm);
     rb_native_mutex_destroy(&vm->thread_destruct_lock);
+    if (0) {
+        /* may be held by running threads */
+        rb_native_mutex_destroy(&vm->waitpid_lock);
+    }
 }
 
 void
@@ -4131,6 +4135,9 @@ rb_gc_set_stack_end(VALUE **stack_end_p)
 #endif
 
 
+/* signal.c */
+void ruby_sigchld_handler(rb_vm_t *);
+
 /*
  *
  */
@@ -4163,6 +4170,7 @@ timer_thread_function(void *arg)
     rb_native_mutex_unlock(&vm->thread_destruct_lock);
 
     /* check signal */
+    ruby_sigchld_handler(vm);
     rb_threadptr_check_signal(vm->main_thread);
 
 #if 0
@@ -4247,6 +4255,9 @@ rb_thread_atfork_internal(rb_thread_t *th, void (*atfork)(rb_thread_t *, const r
     }
     rb_vm_living_threads_init(vm);
     rb_vm_living_threads_insert(vm, th);
+
+    /* may be held by MJIT threads in parent */
+    rb_native_mutex_initialize(&vm->waitpid_lock);
     vm->fork_gen++;
 
     vm->sleeper = 0;
@@ -4999,6 +5010,7 @@ Init_Thread(void)
 	    gvl_init(th->vm);
 	    gvl_acquire(th->vm, th);
             rb_native_mutex_initialize(&th->vm->thread_destruct_lock);
+            rb_native_mutex_initialize(&th->vm->waitpid_lock);
             rb_native_mutex_initialize(&th->interrupt_lock);
 
 	    th->pending_interrupt_queue = rb_ary_tmp_new(0);
@@ -5302,3 +5314,25 @@ rb_uninterruptible(VALUE (*b_proc)(ANYARGS), VALUE data)
 
     return rb_ensure(b_proc, data, rb_ary_pop, cur_th->pending_interrupt_mask_stack);
 }
+
+#ifndef USE_NATIVE_SLEEP_COND
+#  define USE_NATIVE_SLEEP_COND (0)
+#endif
+
+#if !USE_NATIVE_SLEEP_COND
+rb_nativethread_cond_t *
+rb_sleep_cond_get(const rb_execution_context_t *ec)
+{
+    rb_nativethread_cond_t *cond = ALLOC(rb_nativethread_cond_t);
+    rb_native_cond_initialize(cond);
+
+    return cond;
+}
+
+void
+rb_sleep_cond_put(rb_nativethread_cond_t *cond)
+{
+    rb_native_cond_destroy(cond);
+    xfree(cond);
+}
+#endif /* !USE_NATIVE_SLEEP_COND */