External thread suspension (again)

[Keith Seitz <keiths at redhat dot com>]

Including GC list

-------- Original Message --------
Subject: Re: [RFC] GC: external thread suspension
Date: Thu, 25 May 2006 12:39:58 -0700
From: Keith Seitz <keiths@redhat.com>
To: Java Patch List <java-patches@gcc.gnu.org>

Okay, since it has been relatively quiet for the past week, I thought I
would turn this into an official RFA.

I'm going to be conservative, and offer up for approval the patch
suggested by Hans Boehm, using GC_start/end_blocking. It is much simpler
than my original patch.

In order to modify gc.h, it looks like I need to ifdef stuff. Since I've
only done this for pthreads, I've made a best guess as to the proper
conditions. Let me know if there are any problems with this.

Keith

ChangeLog
2006-05-25  Keith Seitz  <keiths@redhat.com>

          * pthread_stop_world.c (GC_suspend_handler): Redirect to
suspension
          routine if signal is received and thread is flagged SUSPENDED.
          (GC_suspend_self): New function.
          (GC_suspend_thread): New function.
          (GC_resume_thread): New function.
          * include/gc.h (GC_suspend_self): Declare.
          (GC_suspend_thread): Declare.
          (GC_resumet_thread): Declare.
          * include/private/pthread_support.h (SUSPENDED): New GC_thread
          flag.



Index: include/gc.h
===================================================================
--- include/gc.h	(revision 114118)
+++ include/gc.h	(working copy)
@@ -1040,4 +1040,15 @@
     }  /* end of extern "C" */
 #endif
 
+/* External thread suspension support. These functions do not implement
+ * suspension counts or any other higher-level abstraction. Threads which
+ * have been suspended numerous times will resume with the very first call
+ * to GC_resume_thread.
+ */
+#if defined(GC_PTHREADS) && !defined(GC_SOLARIS_THREADS) \
+  && !defined(GC_WIN32_THREADS) && !defined(GC_DARWIN_THREADS)
+GC_API void GC_suspend_self GC_PROTO((void));
+GC_API void GC_suspend_thread GC_PROTO((pthread_t));
+GC_API void GC_resume_thread GC_PROTO((pthread_t));
+#endif
 #endif /* _GC_H */
Index: include/private/pthread_support.h
===================================================================
--- include/private/pthread_support.h	(revision 114118)
+++ include/private/pthread_support.h	(working copy)
@@ -33,6 +33,7 @@
 #	define FINISHED 1   	/* Thread has exited.	*/
 #	define DETACHED 2	/* Thread is intended to be detached.	*/
 #	define MAIN_THREAD 4	/* True for the original thread only.	*/
+#       define SUSPENDED 8      /* True if thread was suspended externally */
     short thread_blocked;	/* Protected by GC lock.		*/
     				/* Treated as a boolean value.  If set,	*/
     				/* thread will acquire GC lock before	*/
Index: pthread_stop_world.c
===================================================================
--- pthread_stop_world.c	(revision 114118)
+++ pthread_stop_world.c	(working copy)
@@ -127,9 +127,14 @@
 
 void GC_suspend_handler(int sig)
 {
-  int old_errno = errno;
-  GC_with_callee_saves_pushed(GC_suspend_handler_inner, (ptr_t)(word)sig);
-  errno = old_errno;
+  GC_thread me = GC_lookup_thread (pthread_self());
+  if (me -> flags & SUSPENDED)
+    GC_suspend_self();
+  else {
+    int old_errno = errno;
+    GC_with_callee_saves_pushed(GC_suspend_handler_inner, (ptr_t)(word)sig);
+    errno = old_errno;
+  }
 }
 
 #else
@@ -137,9 +142,14 @@
 /* in the signal handler frame.						*/
 void GC_suspend_handler(int sig)
 {
-  int old_errno = errno;
-  GC_suspend_handler_inner((ptr_t)(word)sig);
-  errno = old_errno;
+  GC_thread me = GC_lookup_thread(pthread_self());
+  if (me -> flags & SUSPENDED)
+    GC_suspend_self();
+  else {
+    int old_errno = errno;
+    GC_suspend_handler_inner((ptr_t)(word)sig);
+    errno = old_errno;
+  }
 }
 #endif
 
@@ -430,6 +440,36 @@
     GC_stopping_thread = 0;  /* debugging only */
 }
 
+void GC_suspend_self() {
+  GC_thread me = GC_lookup_thread(pthread_self());
+  struct timespec t;
+  t.tv_sec = 0;
+  t.tv_nsec = 1000 * 1000 * 50;
+  me -> flags |= SUSPENDED;
+  GC_start_blocking();
+  while (me -> flags & SUSPENDED)
+    nanosleep(&t, NULL);
+  GC_end_blocking();
+}
+
+void GC_suspend_thread(pthread_t thread) {
+  int result;
+  GC_thread t = GC_lookup_thread(thread);
+  result = pthread_kill (t -> id, SIG_SUSPEND);
+  switch (result) {
+      case ESRCH:
+      case 0:
+          break;
+      default:
+          ABORT("pthread_kill failed");
+  }
+}
+
+void GC_resume_thread(pthread_t thread) {
+  GC_thread t = GC_lookup_thread(thread);
+  t -> flags &= ~SUSPENDED;
+}
+
 /* Caller holds allocation lock, and has held it continuously since	*/
 /* the world stopped.							*/
 void GC_start_world()