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-rw-r--r--rts/Capability.c19
-rw-r--r--rts/Capability.h13
-rw-r--r--rts/HeapStackCheck.cmm11
-rw-r--r--rts/Interpreter.c5
-rw-r--r--rts/PrimOps.cmm6
-rw-r--r--rts/Schedule.c2
-rw-r--r--rts/StgStartup.cmm4
-rw-r--r--rts/Threads.c10
-rw-r--r--rts/posix/Signals.c2
9 files changed, 52 insertions, 20 deletions
diff --git a/rts/Capability.c b/rts/Capability.c
index a81d71073a..bd6d56ff00 100644
--- a/rts/Capability.c
+++ b/rts/Capability.c
@@ -294,10 +294,10 @@ initCapabilities( void )
void setContextSwitches(void)
{
- nat i;
- for (i=0; i < n_capabilities; i++) {
- capabilities[i].context_switch = 1;
- }
+ nat i;
+ for (i=0; i < n_capabilities; i++) {
+ contextSwitchCapability(&capabilities[i]);
+ }
}
/* ----------------------------------------------------------------------------
@@ -482,14 +482,17 @@ waitForReturnCapability (Capability **pCap, Task *task)
if (!cap->running_task) {
nat i;
// otherwise, search for a free capability
+ cap = NULL;
for (i = 0; i < n_capabilities; i++) {
- cap = &capabilities[i];
- if (!cap->running_task) {
+ if (!capabilities[i].running_task) {
+ cap = &capabilities[i];
break;
}
}
- // Can't find a free one, use last_free_capability.
- cap = last_free_capability;
+ if (cap == NULL) {
+ // Can't find a free one, use last_free_capability.
+ cap = last_free_capability;
+ }
}
// record the Capability as the one this Task is now assocated with.
diff --git a/rts/Capability.h b/rts/Capability.h
index 77132e318e..0f61fad913 100644
--- a/rts/Capability.h
+++ b/rts/Capability.h
@@ -276,6 +276,7 @@ extern void grabCapability (Capability **pCap);
// cause all capabilities to context switch as soon as possible.
void setContextSwitches(void);
+INLINE_HEADER void contextSwitchCapability(Capability *cap);
// Free all capabilities
void freeCapabilities (void);
@@ -322,4 +323,16 @@ discardSparksCap (Capability *cap)
{ return discardSparks(cap->sparks); }
#endif
+INLINE_HEADER void
+contextSwitchCapability (Capability *cap)
+{
+ // setting HpLim to NULL ensures that the next heap check will
+ // fail, and the thread will return to the scheduler.
+ cap->r.rHpLim = NULL;
+ // But just in case it didn't work (the target thread might be
+ // modifying HpLim at the same time), we set the end-of-block
+ // context-switch flag too:
+ cap->context_switch = 1;
+}
+
#endif /* CAPABILITY_H */
diff --git a/rts/HeapStackCheck.cmm b/rts/HeapStackCheck.cmm
index 94cec387cc..10baca23c6 100644
--- a/rts/HeapStackCheck.cmm
+++ b/rts/HeapStackCheck.cmm
@@ -23,8 +23,11 @@ import LeaveCriticalSection;
*
* On discovering that a stack or heap check has failed, we do the following:
*
- * - If the context_switch flag is set, indicating that there are more
- * threads waiting to run, we yield to the scheduler
+ * - If HpLim==0, indicating that we should context-switch, we yield
+ * to the scheduler (return ThreadYielding).
+ *
+ * - If the context_switch flag is set (the backup plan if setting HpLim
+ * to 0 didn't trigger a context switch), we yield to the scheduler
* (return ThreadYielding).
*
* - If Hp > HpLim, we've had a heap check failure. This means we've
@@ -60,6 +63,10 @@ import LeaveCriticalSection;
#define GC_GENERIC \
DEBUG_ONLY(foreign "C" heapCheckFail()); \
if (Hp > HpLim) { \
+ if (HpLim == 0) { \
+ R1 = ThreadYielding; \
+ goto sched; \
+ } \
Hp = Hp - HpAlloc/*in bytes*/; \
if (HpAlloc <= BLOCK_SIZE \
&& bdescr_link(CurrentNursery) != NULL) { \
diff --git a/rts/Interpreter.c b/rts/Interpreter.c
index 1b2d7303ed..1a6e9273e0 100644
--- a/rts/Interpreter.c
+++ b/rts/Interpreter.c
@@ -196,6 +196,9 @@ interpretBCO (Capability* cap)
LOAD_STACK_POINTERS;
+ cap->r.rHpLim = (P_)1; // HpLim is the context-switch flag; when it
+ // goes to zero we must return to the scheduler.
+
// ------------------------------------------------------------------------
// Case 1:
//
@@ -1281,7 +1284,7 @@ run_BCO:
// context switching: sometimes the scheduler can invoke
// the interpreter with context_switch == 1, particularly
// if the -C0 flag has been given on the cmd line.
- if (cap->context_switch) {
+ if (cap->r.rHpLim == NULL) {
Sp--; Sp[0] = (W_)&stg_enter_info;
RETURN_TO_SCHEDULER(ThreadInterpret, ThreadYielding);
}
diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index adb2a643a9..121102c8e1 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -1073,7 +1073,8 @@ forkzh_fast
foreign "C" scheduleThread(MyCapability() "ptr", threadid "ptr") [];
- // switch at the earliest opportunity
+ // context switch soon, but not immediately: we don't want every
+ // forkIO to force a context-switch.
Capability_context_switch(MyCapability()) = 1 :: CInt;
RET_P(threadid);
@@ -1102,7 +1103,8 @@ forkOnzh_fast
foreign "C" scheduleThreadOn(MyCapability() "ptr", cpu, threadid "ptr") [];
- // switch at the earliest opportunity
+ // context switch soon, but not immediately: we don't want every
+ // forkIO to force a context-switch.
Capability_context_switch(MyCapability()) = 1 :: CInt;
RET_P(threadid);
diff --git a/rts/Schedule.c b/rts/Schedule.c
index 47636a3ff4..040d16f25a 100644
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -1268,7 +1268,7 @@ scheduleHandleHeapOverflow( Capability *cap, StgTSO *t )
"--<< thread %ld (%s) stopped: HeapOverflow",
(long)t->id, whatNext_strs[t->what_next]);
- if (cap->context_switch) {
+ if (cap->r.rHpLim == NULL || cap->context_switch) {
// Sometimes we miss a context switch, e.g. when calling
// primitives in a tight loop, MAYBE_GC() doesn't check the
// context switch flag, and we end up waiting for a GC.
diff --git a/rts/StgStartup.cmm b/rts/StgStartup.cmm
index 16e5c62801..c3c0bc3dd7 100644
--- a/rts/StgStartup.cmm
+++ b/rts/StgStartup.cmm
@@ -28,9 +28,7 @@
ASSERT(Hp != 0); \
ASSERT(Sp != 0); \
ASSERT(SpLim != 0); \
- ASSERT(HpLim != 0); \
- ASSERT(SpLim - WDS(RESERVED_STACK_WORDS) <= Sp); \
- ASSERT(HpLim >= Hp);
+ ASSERT(SpLim - WDS(RESERVED_STACK_WORDS) <= Sp);
/* -----------------------------------------------------------------------------
Returning from the STG world.
diff --git a/rts/Threads.c b/rts/Threads.c
index 2c7b2beb86..936b90e884 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -505,8 +505,10 @@ unblockOne_ (Capability *cap, StgTSO *tso,
}
tso->cap = cap;
appendToRunQueue(cap,tso);
- // we're holding a newly woken thread, make sure we context switch
- // quickly so we can migrate it if necessary.
+
+ // context-switch soonish so we can migrate the new thread if
+ // necessary. NB. not contextSwitchCapability(cap), which would
+ // force a context switch immediately.
cap->context_switch = 1;
} else {
// we'll try to wake it up on the Capability it was last on.
@@ -514,6 +516,10 @@ unblockOne_ (Capability *cap, StgTSO *tso,
}
#else
appendToRunQueue(cap,tso);
+
+ // context-switch soonish so we can migrate the new thread if
+ // necessary. NB. not contextSwitchCapability(cap), which would
+ // force a context switch immediately.
cap->context_switch = 1;
#endif
diff --git a/rts/posix/Signals.c b/rts/posix/Signals.c
index 8268e6fe74..6d5ef43278 100644
--- a/rts/posix/Signals.c
+++ b/rts/posix/Signals.c
@@ -214,7 +214,7 @@ generic_handler(int sig USED_IF_THREADS,
stg_exit(EXIT_FAILURE);
}
- MainCapability.context_switch = 1;
+ contextSwitchCapability(&MainCapability);
#endif /* THREADED_RTS */
}
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