improvement to the deadlock detection

When the RTS is idle, as detected by the timer signal, instead of
prodding capabilities from the signal handler (which is not guaranteed
to work - pthread_cond_signal() can't be called from signal handlers),
create a new thread to do it.

diff --git a/ghc/rts/Timer.c b/ghc/rts/Timer.c
index b6414f8..425ada5 100644 (file)
--- a/ghc/rts/Timer.c
+++ b/ghc/rts/Timer.c
@@ -21,6 +21,7 @@
 #include "Timer.h"
 #include "Ticker.h"
 #include "Capability.h"
+#include "OSThreads.h"
 
 /* ticks left before next pre-emptive context switch */
 static int ticks_to_ctxt_switch = 0;
@@ -30,6 +31,10 @@ static int ticks_to_ctxt_switch = 0;
 static int ticks_to_gc = 0;
 #endif
 
+#if defined(THREADED_RTS)
+static void OSThreadProcAttr proddingThread(void *p);
+#endif
+
 /*
  * Function: handle_tick()
  *
@@ -60,7 +65,8 @@ handle_tick(int unused STG_UNUSED)
              recent_activity = ACTIVITY_MAYBE_NO;
              ticks_to_gc = RtsFlags.GcFlags.idleGCDelayTicks;
              break;
-         case ACTIVITY_MAYBE_NO:
+         case ACTIVITY_MAYBE_NO: {
+             OSThreadId id;
              if (ticks_to_gc == 0) break; /* 0 ==> no idle GC */
              ticks_to_gc--;
              if (ticks_to_gc == 0) {
@@ -69,14 +75,15 @@ handle_tick(int unused STG_UNUSED)
                  blackholes_need_checking = rtsTrue;
                  /* hack: re-use the blackholes_need_checking flag */
 
-                 /* ToDo: this doesn't work.  Can't invoke
-                  * pthread_cond_signal from a signal handler.
-                  * Furthermore, we can't prod a capability that we
-                  * might be holding.  What can we do?
+                 /* We can't prod the Capability from inside the
+                  * signal handler, because pthread_cond_signal()
+                  * doesn't work from signal handlers.  Let's hope
+                  * that pthread_create() works:
                   */
-                 prodOneCapability();
+                 createOSThread(&id, proddingThread, NULL);
              }
              break;
+         }
          default:
              break;
          }
@@ -85,6 +92,15 @@ handle_tick(int unused STG_UNUSED)
   }
 }
 
+#if defined(THREADED_RTS)
+static void OSThreadProcAttr
+proddingThread(void *p STG_UNUSED)
+{
+    prodOneCapability();
+    // and exit again.
+}
+#endif
+
 int
 startTimer(nat ms)
 {