Re: [RFA] Boehm GC support addition for debugging

[Keith Seitz <keiths at redhat dot com>]

Bryce McKinlay wrote:
> Keith Seitz wrote:
> > Hmm. Okay, well, so should I consider the GC patch "approved" _for 
> > now_ (or at least until it is a problem for me)?
>
> Yes, it is approved for libgcj trunk.

Okay, I have committed this. I made one small change to accommodate the 
recent _Jv_ThreadDesc_t patch you committed: I've eliminated 
GC_suspend_self. GC_suspend_thread will check for this case itself. 
[That saves me from having to do a pthread_self in otherwise generic code.]

Thank you for all your help with this.

Keith

ChangeLog

2006-06-21  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.
        (suspend_self): New function.
        (GC_suspend_thread): New function.
        (GC_resume_thread): New function.
        * include/gc.h (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 114865)
+++ include/gc.h	(working copy)
@@ -1040,4 +1040,14 @@
     }  /* 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_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 114865)
+++ 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 114865)
+++ pthread_stop_world.c	(working copy)
@@ -13,6 +13,8 @@
   /* Doesn't exist on HP/UX 11.11. */
 #endif
 
+void suspend_self();
+
 #if DEBUG_THREADS
 
 #ifndef NSIG
@@ -127,9 +129,14 @@
 
 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)
+    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 +144,14 @@
 /* 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)
+    suspend_self();
+  else {
+    int old_errno = errno;
+    GC_suspend_handler_inner((ptr_t)(word)sig);
+    errno = old_errno;
+  }
 }
 #endif
 
@@ -430,6 +442,47 @@
     GC_stopping_thread = 0;  /* debugging only */
 }
 
+void suspend_self() {
+  GC_thread me = GC_lookup_thread(pthread_self());
+  if (me == NULL)
+    ABORT("attempting to suspend unknown thread");
+
+  me -> flags |= SUSPENDED;
+  GC_start_blocking();
+  while (me -> flags & SUSPENDED)
+    GC_brief_async_signal_safe_sleep();
+  GC_end_blocking();
+}
+
+void GC_suspend_thread(pthread_t thread) {
+  if (thread == pthread_self())
+    suspend_self();
+  else {
+    int result;
+    GC_thread t = GC_lookup_thread(thread);
+    if (t == NULL)
+      ABORT("attempting to suspend unknown thread");
+
+    t -> flags |= SUSPENDED;
+    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);
+  if (t == NULL)
+    ABORT("attempting to resume unknown thread");
+
+  t -> flags &= ~SUSPENDED;
+}
+
 /* Caller holds allocation lock, and has held it continuously since	*/
 /* the world stopped.							*/
 void GC_start_world()