From d9275dd06ee24575ff50a6696fe7fe1e1fa91ac7 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Thu, 4 Jun 2009 09:05:53 +0000
Subject: [PATCH] Lock the StablePtr table during GC Allows hs_free_fun_ptr()
 to be called by a separate thread

---
 includes/Stable.h |    3 +++
 rts/Stable.c      |   17 +++++++++++++++++
 rts/sm/GC.c       |    6 ++++++
 3 files changed, 26 insertions(+)

diff --git a/includes/Stable.h b/includes/Stable.h
index 5404bab..9752a53 100644
--- a/includes/Stable.h
+++ b/includes/Stable.h
@@ -57,4 +57,7 @@ extern void    threadStablePtrTable  ( evac_fn evac, void *user );
 extern void    gcStablePtrTable      ( void );
 extern void    updateStablePtrTable  ( rtsBool full );
 
+extern void    stablePtrPreGC        ( void );
+extern void    stablePtrPostGC       ( void );
+
 #endif
diff --git a/rts/Stable.c b/rts/Stable.c
index 94a756a..97796b8 100644
--- a/rts/Stable.c
+++ b/rts/Stable.c
@@ -316,6 +316,23 @@ enlargeStablePtrTable(void)
 }
 
 /* -----------------------------------------------------------------------------
+ * We must lock the StablePtr table during GC, to prevent simultaneous
+ * calls to freeStablePtr().
+ * -------------------------------------------------------------------------- */
+
+void
+stablePtrPreGC(void)
+{
+    ACQUIRE_LOCK(&stable_mutex);
+}
+
+void
+stablePtrPostGC(void)
+{
+    RELEASE_LOCK(&stable_mutex);
+}
+
+/* -----------------------------------------------------------------------------
  * Treat stable pointers as roots for the garbage collector.
  *
  * A stable pointer is any stable name entry with a ref > 0.  We'll
diff --git a/rts/sm/GC.c b/rts/sm/GC.c
index e0c8b05..cfe4c6b 100644
--- a/rts/sm/GC.c
+++ b/rts/sm/GC.c
@@ -215,6 +215,9 @@ GarbageCollect (rtsBool force_major_gc,
   // tell the STM to discard any cached closures it's hoping to re-use
   stmPreGCHook();
 
+  // lock the StablePtr table
+  stablePtrPreGC();
+
 #ifdef DEBUG
   mutlist_MUTVARS = 0;
   mutlist_MUTARRS = 0;
@@ -794,6 +797,9 @@ SET_GCT(gc_threads[0]);
   slop = calcLiveBlocks() * BLOCK_SIZE_W - live;
   stat_endGC(allocated, live, copied, N, max_copied, avg_copied, slop);
 
+  // unlock the StablePtr table
+  stablePtrPostGC();
+
   // Guess which generation we'll collect *next* time
   initialise_N(force_major_gc);
 
-- 
1.7.10.4