Add a write barrier to the TSO link field (#1589)

5 files changed, 28 insertions, 7 deletions

diff --git a/includes/Cmm.h b/includes/Cmm.h
index 4cfb432811..7a68a517fe 100644
--- a/includes/Cmm.h
+++ b/includes/Cmm.h
@@ -544,9 +544,6 @@
 #define END_TSO_QUEUE             stg_END_TSO_QUEUE_closure
 #define END_INVARIANT_CHECK_QUEUE stg_END_INVARIANT_CHECK_QUEUE_closure
 
-#define dirtyTSO(tso) \
-    StgTSO_flags(tso) = StgTSO_flags(tso) | TSO_DIRTY::I32;
-
 #define recordMutableCap(p, gen, regs)					\
   W_ __bd;								\
   W_ mut_list;								\
diff --git a/includes/Constants.h b/includes/Constants.h
index e0949cbd1f..66254f4114 100644
--- a/includes/Constants.h
+++ b/includes/Constants.h
@@ -260,6 +260,11 @@
 #define TSO_INTERRUPTIBLE 8
 #define TSO_STOPPED_ON_BREAKPOINT 16 
 
+/*
+ * TSO_LINK_DIRTY is set when a TSO's link field is modified
+ */
+#define TSO_LINK_DIRTY 32
+
 /* -----------------------------------------------------------------------------
    RET_DYN stack frames
    -------------------------------------------------------------------------- */
diff --git a/includes/RtsExternal.h b/includes/RtsExternal.h
index b95276168a..c6fd74ac8d 100644
--- a/includes/RtsExternal.h
+++ b/includes/RtsExternal.h
@@ -126,6 +126,4 @@ extern void revertCAFs( void );
 extern void dirty_MUT_VAR(StgRegTable *reg, StgClosure *p);
 extern void dirty_MVAR(StgRegTable *reg, StgClosure *p);
 
-extern void dirty_TSO(StgClosure *tso);
-
 #endif /*  RTSEXTERNAL_H */
diff --git a/includes/TSO.h b/includes/TSO.h
index 088097ea50..c6ec6697d4 100644
--- a/includes/TSO.h
+++ b/includes/TSO.h
@@ -124,7 +124,21 @@ typedef union {
 typedef struct StgTSO_ {
     StgHeader               header;
 
-    struct StgTSO_*         link;       /* Links threads onto blocking queues */
+    /* The link field, for linking threads together in lists (e.g. the
+       run queue on a Capability.
+    */
+    struct StgTSO_*         _link;
+    /*
+       NOTE!!!  do not modify _link directly, it is subject to
+       a write barrier for generational GC.  Instead use the
+       setTSOLink() function.  Exceptions to this rule are:
+
+       * setting the link field to END_TSO_QUEUE
+       * putting a TSO on the blackhole_queue
+       * setting the link field of the currently running TSO, as it
+         will already be dirty.
+    */
+
     struct StgTSO_*         global_link;    /* Links all threads together */
     
     StgWord16               what_next;      /* Values defined in Constants.h */
@@ -172,6 +186,13 @@ typedef struct StgTSO_ {
 } StgTSO;
 
 /* -----------------------------------------------------------------------------
+   functions
+   -------------------------------------------------------------------------- */
+
+extern void dirty_TSO  (Capability *cap, StgTSO *tso);
+extern void setTSOLink (Capability *cap, StgTSO *tso, StgTSO *target);
+
+/* -----------------------------------------------------------------------------
    Invariants:
 
    An active thread has the following properties:
diff --git a/includes/mkDerivedConstants.c b/includes/mkDerivedConstants.c
index 56296ec4f1..51e52f0089 100644
--- a/includes/mkDerivedConstants.c
+++ b/includes/mkDerivedConstants.c
@@ -275,7 +275,7 @@ main(int argc, char *argv[])
     closure_field(StgArrWords, words);
     closure_payload(StgArrWords, payload);
 
-    closure_field(StgTSO, link);
+    closure_field(StgTSO, _link);
     closure_field(StgTSO, global_link);
     closure_field(StgTSO, what_next);
     closure_field(StgTSO, why_blocked);