From: Simon Marlow <marlowsd@gmail.com>
Date: Tue, 18 May 2010 11:32:14 +0000 (+0000)
Subject: Fix #4074 (I hope).
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=f9b4bc220a684a970a58dafa9e57d665d29b4121;p=ghc-hetmet.git

Fix #4074 (I hope).

1. allow multiple threads to call startTimer()/stopTimer() pairs
2. disable the timer around fork() in forkProcess()

A corresponding change to the process package is required.
---

diff --git a/rts/Schedule.c b/rts/Schedule.c
index 66a1388..8db125d 100644
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -1533,10 +1533,14 @@ forkProcess(HsStablePtr *entry
     ACQUIRE_LOCK(&cap->lock);
     ACQUIRE_LOCK(&cap->running_task->lock);
 
+    stopTimer(); // See #4074
+
     pid = fork();
     
     if (pid) { // parent
 	
+        startTimer(); // #4074
+
         RELEASE_LOCK(&sched_mutex);
         RELEASE_LOCK(&cap->lock);
         RELEASE_LOCK(&cap->running_task->lock);
diff --git a/rts/Timer.c b/rts/Timer.c
index dddc754..02d106f 100644
--- a/rts/Timer.c
+++ b/rts/Timer.c
@@ -86,6 +86,15 @@ handle_tick(int unused STG_UNUSED)
 #endif
 }
 
+// This global counter is used to allow multiple threads to stop the
+// timer temporarily with a stopTimer()/startTimer() pair.  If 
+//      timer_enabled  == 0          timer is enabled
+//      timer_disabled == N, N > 0   timer is disabled by N threads
+// When timer_enabled makes a transition to 0, we enable the timer,
+// and when it makes a transition to non-0 we disable it.
+
+static StgWord timer_disabled;
+
 void
 initTimer(void)
 {
@@ -93,21 +102,26 @@ initTimer(void)
     if (RtsFlags.MiscFlags.tickInterval != 0) {
         initTicker(RtsFlags.MiscFlags.tickInterval, handle_tick);
     }
+    timer_disabled = 1;
 }
 
 void
 startTimer(void)
 {
-    if (RtsFlags.MiscFlags.tickInterval != 0) {
-        startTicker();
+    if (atomic_dec(&timer_disabled) == 0) {
+        if (RtsFlags.MiscFlags.tickInterval != 0) {
+            startTicker();
+        }
     }
 }
 
 void
 stopTimer(void)
 {
-    if (RtsFlags.MiscFlags.tickInterval != 0) {
-        stopTicker();
+    if (atomic_inc(&timer_disabled) == 1) {
+        if (RtsFlags.MiscFlags.tickInterval != 0) {
+            stopTicker();
+        }
     }
 }