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Schedule.c
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Schedule.c
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/* ---------------------------------------------------------------------------
*
* (c) The GHC Team, 1998-2006
*
* The scheduler and thread-related functionality
*
* --------------------------------------------------------------------------*/
#include "PosixSource.h"
#define KEEP_LOCKCLOSURE
#include "Rts.h"
#include "sm/Storage.h"
#include "RtsUtils.h"
#include "StgRun.h"
#include "Schedule.h"
#include "Interpreter.h"
#include "Printer.h"
#include "RtsSignals.h"
#include "sm/Sanity.h"
#include "Stats.h"
#include "STM.h"
#include "Prelude.h"
#include "ThreadLabels.h"
#include "Updates.h"
#include "Proftimer.h"
#include "ProfHeap.h"
#include "Weak.h"
#include "sm/GC.h" // waitForGcThreads, releaseGCThreads, N
#include "sm/GCThread.h"
#include "Sparks.h"
#include "Capability.h"
#include "Task.h"
#include "AwaitEvent.h"
#if defined(mingw32_HOST_OS)
#include "win32/IOManager.h"
#endif
#include "Trace.h"
#include "RaiseAsync.h"
#include "Threads.h"
#include "Timer.h"
#include "ThreadPaused.h"
#include "Messages.h"
#include "Stable.h"
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#ifdef TRACING
#include "eventlog/EventLog.h"
#endif
/* -----------------------------------------------------------------------------
* Global variables
* -------------------------------------------------------------------------- */
#if !defined(THREADED_RTS)
// Blocked/sleeping thrads
StgTSO *blocked_queue_hd = NULL;
StgTSO *blocked_queue_tl = NULL;
StgTSO *sleeping_queue = NULL; // perhaps replace with a hash table?
#endif
/* Set to true when the latest garbage collection failed to reclaim
* enough space, and the runtime should proceed to shut itself down in
* an orderly fashion (emitting profiling info etc.)
*/
rtsBool heap_overflow = rtsFalse;
/* flag that tracks whether we have done any execution in this time slice.
* LOCK: currently none, perhaps we should lock (but needs to be
* updated in the fast path of the scheduler).
*
* NB. must be StgWord, we do xchg() on it.
*/
volatile StgWord recent_activity = ACTIVITY_YES;
/* if this flag is set as well, give up execution
* LOCK: none (changes monotonically)
*/
volatile StgWord sched_state = SCHED_RUNNING;
/* This is used in `TSO.h' and gcc 2.96 insists that this variable actually
* exists - earlier gccs apparently didn't.
* -= chak
*/
StgTSO dummy_tso;
/*
* This mutex protects most of the global scheduler data in
* the THREADED_RTS runtime.
*/
#if defined(THREADED_RTS)
Mutex sched_mutex;
#endif
#if !defined(mingw32_HOST_OS)
#define FORKPROCESS_PRIMOP_SUPPORTED
#endif
// Local stats
#ifdef THREADED_RTS
static nat n_failed_trygrab_idles = 0, n_idle_caps = 0;
#endif
/* -----------------------------------------------------------------------------
* static function prototypes
* -------------------------------------------------------------------------- */
static Capability *schedule (Capability *initialCapability, Task *task);
//
// These functions all encapsulate parts of the scheduler loop, and are
// abstracted only to make the structure and control flow of the
// scheduler clearer.
//
static void schedulePreLoop (void);
static void scheduleFindWork (Capability **pcap);
#if defined(THREADED_RTS)
static void scheduleYield (Capability **pcap, Task *task);
#endif
#if defined(THREADED_RTS)
static nat requestSync (Capability **pcap, Task *task, nat sync_type);
static void acquireAllCapabilities(Capability *cap, Task *task);
static void releaseAllCapabilities(nat n, Capability *cap, Task *task);
static void startWorkerTasks (nat from USED_IF_THREADS, nat to USED_IF_THREADS);
#endif
static void scheduleStartSignalHandlers (Capability *cap);
static void scheduleCheckBlockedThreads (Capability *cap);
static void scheduleProcessInbox(Capability **cap);
static void scheduleDetectDeadlock (Capability **pcap, Task *task);
static void schedulePushWork(Capability *cap, Task *task);
#if defined(THREADED_RTS)
static void scheduleActivateSpark(Capability *cap);
#endif
static void schedulePostRunThread(Capability *cap, StgTSO *t);
static rtsBool scheduleHandleHeapOverflow( Capability *cap, StgTSO *t );
static rtsBool scheduleHandleYield( Capability *cap, StgTSO *t,
nat prev_what_next );
static void scheduleHandleThreadBlocked( StgTSO *t );
static rtsBool scheduleHandleThreadFinished( Capability *cap, Task *task,
StgTSO *t );
static rtsBool scheduleNeedHeapProfile(rtsBool ready_to_gc);
static void scheduleDoGC(Capability **pcap, Task *task, rtsBool force_major);
static void deleteThread (Capability *cap, StgTSO *tso);
static void deleteAllThreads (Capability *cap);
#ifdef FORKPROCESS_PRIMOP_SUPPORTED
static void deleteThread_(Capability *cap, StgTSO *tso);
#endif
/* ---------------------------------------------------------------------------
Main scheduling loop.
We use round-robin scheduling, each thread returning to the
scheduler loop when one of these conditions is detected:
* out of heap space
* timer expires (thread yields)
* thread blocks
* thread ends
* stack overflow
------------------------------------------------------------------------ */
static Capability *
schedule (Capability *initialCapability, Task *task)
{
StgTSO *t;
Capability *cap;
StgThreadReturnCode ret;
nat prev_what_next;
rtsBool ready_to_gc;
#if defined(THREADED_RTS)
rtsBool first = rtsTrue;
#endif
cap = initialCapability;
// Pre-condition: this task owns initialCapability.
// The sched_mutex is *NOT* held
// NB. on return, we still hold a capability.
debugTrace (DEBUG_sched, "cap %d: schedule()", initialCapability->no);
schedulePreLoop();
// -----------------------------------------------------------
// Scheduler loop starts here:
while (1) {
// Check whether we have re-entered the RTS from Haskell without
// going via suspendThread()/resumeThread (i.e. a 'safe' foreign
// call).
if (cap->in_haskell) {
errorBelch("schedule: re-entered unsafely.\n"
" Perhaps a 'foreign import unsafe' should be 'safe'?");
stg_exit(EXIT_FAILURE);
}
// The interruption / shutdown sequence.
//
// In order to cleanly shut down the runtime, we want to:
// * make sure that all main threads return to their callers
// with the state 'Interrupted'.
// * clean up all OS threads assocated with the runtime
// * free all memory etc.
//
// So the sequence for ^C goes like this:
//
// * ^C handler sets sched_state := SCHED_INTERRUPTING and
// arranges for some Capability to wake up
//
// * all threads in the system are halted, and the zombies are
// placed on the run queue for cleaning up. We acquire all
// the capabilities in order to delete the threads, this is
// done by scheduleDoGC() for convenience (because GC already
// needs to acquire all the capabilities). We can't kill
// threads involved in foreign calls.
//
// * somebody calls shutdownHaskell(), which calls exitScheduler()
//
// * sched_state := SCHED_SHUTTING_DOWN
//
// * all workers exit when the run queue on their capability
// drains. All main threads will also exit when their TSO
// reaches the head of the run queue and they can return.
//
// * eventually all Capabilities will shut down, and the RTS can
// exit.
//
// * We might be left with threads blocked in foreign calls,
// we should really attempt to kill these somehow (TODO);
switch (sched_state) {
case SCHED_RUNNING:
break;
case SCHED_INTERRUPTING:
debugTrace(DEBUG_sched, "SCHED_INTERRUPTING");
/* scheduleDoGC() deletes all the threads */
scheduleDoGC(&cap,task,rtsFalse);
// after scheduleDoGC(), we must be shutting down. Either some
// other Capability did the final GC, or we did it above,
// either way we can fall through to the SCHED_SHUTTING_DOWN
// case now.
ASSERT(sched_state == SCHED_SHUTTING_DOWN);
// fall through
case SCHED_SHUTTING_DOWN:
debugTrace(DEBUG_sched, "SCHED_SHUTTING_DOWN");
// If we are a worker, just exit. If we're a bound thread
// then we will exit below when we've removed our TSO from
// the run queue.
if (!isBoundTask(task) && emptyRunQueue(cap)) {
return cap;
}
break;
default:
barf("sched_state: %d", sched_state);
}
scheduleFindWork(&cap);
/* work pushing, currently relevant only for THREADED_RTS:
(pushes threads, wakes up idle capabilities for stealing) */
schedulePushWork(cap,task);
scheduleDetectDeadlock(&cap,task);
// Normally, the only way we can get here with no threads to
// run is if a keyboard interrupt received during
// scheduleCheckBlockedThreads() or scheduleDetectDeadlock().
// Additionally, it is not fatal for the
// threaded RTS to reach here with no threads to run.
//
// win32: might be here due to awaitEvent() being abandoned
// as a result of a console event having been delivered.
#if defined(THREADED_RTS)
if (first)
{
// XXX: ToDo
// // don't yield the first time, we want a chance to run this
// // thread for a bit, even if there are others banging at the
// // door.
// first = rtsFalse;
// ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
}
scheduleYield(&cap,task);
if (emptyRunQueue(cap)) continue; // look for work again
#endif
#if !defined(THREADED_RTS) && !defined(mingw32_HOST_OS)
if ( emptyRunQueue(cap) ) {
ASSERT(sched_state >= SCHED_INTERRUPTING);
}
#endif
//
// Get a thread to run
//
t = popRunQueue(cap);
// Sanity check the thread we're about to run. This can be
// expensive if there is lots of thread switching going on...
IF_DEBUG(sanity,checkTSO(t));
#if defined(THREADED_RTS)
// Check whether we can run this thread in the current task.
// If not, we have to pass our capability to the right task.
{
InCall *bound = t->bound;
if (bound) {
if (bound->task == task) {
// yes, the Haskell thread is bound to the current native thread
} else {
debugTrace(DEBUG_sched,
"thread %lu bound to another OS thread",
(unsigned long)t->id);
// no, bound to a different Haskell thread: pass to that thread
pushOnRunQueue(cap,t);
continue;
}
} else {
// The thread we want to run is unbound.
if (task->incall->tso) {
debugTrace(DEBUG_sched,
"this OS thread cannot run thread %lu",
(unsigned long)t->id);
// no, the current native thread is bound to a different
// Haskell thread, so pass it to any worker thread
pushOnRunQueue(cap,t);
continue;
}
}
}
#endif
// If we're shutting down, and this thread has not yet been
// killed, kill it now. This sometimes happens when a finalizer
// thread is created by the final GC, or a thread previously
// in a foreign call returns.
if (sched_state >= SCHED_INTERRUPTING &&
!(t->what_next == ThreadComplete || t->what_next == ThreadKilled)) {
deleteThread(cap,t);
}
// If this capability is disabled, migrate the thread away rather
// than running it. NB. but not if the thread is bound: it is
// really hard for a bound thread to migrate itself. Believe me,
// I tried several ways and couldn't find a way to do it.
// Instead, when everything is stopped for GC, we migrate all the
// threads on the run queue then (see scheduleDoGC()).
//
// ToDo: what about TSO_LOCKED? Currently we're migrating those
// when the number of capabilities drops, but we never migrate
// them back if it rises again. Presumably we should, but after
// the thread has been migrated we no longer know what capability
// it was originally on.
#ifdef THREADED_RTS
if (cap->disabled && !t->bound) {
Capability *dest_cap = capabilities[cap->no % enabled_capabilities];
migrateThread(cap, t, dest_cap);
continue;
}
#endif
/* context switches are initiated by the timer signal, unless
* the user specified "context switch as often as possible", with
* +RTS -C0
*/
if (RtsFlags.ConcFlags.ctxtSwitchTicks == 0
&& !emptyThreadQueues(cap)) {
cap->context_switch = 1;
}
run_thread:
// CurrentTSO is the thread to run. It might be different if we
// loop back to run_thread, so make sure to set CurrentTSO after
// that.
cap->r.rCurrentTSO = t;
startHeapProfTimer();
// ----------------------------------------------------------------------
// Run the current thread
ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
ASSERT(t->cap == cap);
ASSERT(t->bound ? t->bound->task->cap == cap : 1);
prev_what_next = t->what_next;
errno = t->saved_errno;
#if mingw32_HOST_OS
SetLastError(t->saved_winerror);
#endif
// reset the interrupt flag before running Haskell code
cap->interrupt = 0;
cap->in_haskell = rtsTrue;
cap->idle = 0;
dirty_TSO(cap,t);
dirty_STACK(cap,t->stackobj);
switch (recent_activity)
{
case ACTIVITY_DONE_GC: {
// ACTIVITY_DONE_GC means we turned off the timer signal to
// conserve power (see #1623). Re-enable it here.
nat prev;
prev = xchg((P_)&recent_activity, ACTIVITY_YES);
if (prev == ACTIVITY_DONE_GC) {
#ifndef PROFILING
startTimer();
#endif
}
break;
}
case ACTIVITY_INACTIVE:
// If we reached ACTIVITY_INACTIVE, then don't reset it until
// we've done the GC. The thread running here might just be
// the IO manager thread that handle_tick() woke up via
// wakeUpRts().
break;
default:
recent_activity = ACTIVITY_YES;
}
traceEventRunThread(cap, t);
switch (prev_what_next) {
case ThreadKilled:
case ThreadComplete:
/* Thread already finished, return to scheduler. */
ret = ThreadFinished;
break;
case ThreadRunGHC:
{
StgRegTable *r;
r = StgRun((StgFunPtr) stg_returnToStackTop, &cap->r);
cap = regTableToCapability(r);
ret = r->rRet;
break;
}
case ThreadInterpret:
cap = interpretBCO(cap);
ret = cap->r.rRet;
break;
default:
barf("schedule: invalid what_next field");
}
cap->in_haskell = rtsFalse;
// The TSO might have moved, eg. if it re-entered the RTS and a GC
// happened. So find the new location:
t = cap->r.rCurrentTSO;
// And save the current errno in this thread.
// XXX: possibly bogus for SMP because this thread might already
// be running again, see code below.
t->saved_errno = errno;
#if mingw32_HOST_OS
// Similarly for Windows error code
t->saved_winerror = GetLastError();
#endif
if (ret == ThreadBlocked) {
if (t->why_blocked == BlockedOnBlackHole) {
StgTSO *owner = blackHoleOwner(t->block_info.bh->bh);
traceEventStopThread(cap, t, t->why_blocked + 6,
owner != NULL ? owner->id : 0);
} else {
traceEventStopThread(cap, t, t->why_blocked + 6, 0);
}
} else {
traceEventStopThread(cap, t, ret, 0);
}
ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
ASSERT(t->cap == cap);
// ----------------------------------------------------------------------
// Costs for the scheduler are assigned to CCS_SYSTEM
stopHeapProfTimer();
#if defined(PROFILING)
cap->r.rCCCS = CCS_SYSTEM;
#endif
schedulePostRunThread(cap,t);
ready_to_gc = rtsFalse;
switch (ret) {
case HeapOverflow:
ready_to_gc = scheduleHandleHeapOverflow(cap,t);
break;
case StackOverflow:
// just adjust the stack for this thread, then pop it back
// on the run queue.
threadStackOverflow(cap, t);
pushOnRunQueue(cap,t);
break;
case ThreadYielding:
if (scheduleHandleYield(cap, t, prev_what_next)) {
// shortcut for switching between compiler/interpreter:
goto run_thread;
}
break;
case ThreadBlocked:
scheduleHandleThreadBlocked(t);
break;
case ThreadFinished:
if (scheduleHandleThreadFinished(cap, task, t)) return cap;
ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task);
break;
default:
barf("schedule: invalid thread return code %d", (int)ret);
}
if (ready_to_gc || scheduleNeedHeapProfile(ready_to_gc)) {
scheduleDoGC(&cap,task,rtsFalse);
}
} /* end of while() */
}
/* -----------------------------------------------------------------------------
* Run queue operations
* -------------------------------------------------------------------------- */
void
removeFromRunQueue (Capability *cap, StgTSO *tso)
{
if (tso->block_info.prev == END_TSO_QUEUE) {
ASSERT(cap->run_queue_hd == tso);
cap->run_queue_hd = tso->_link;
} else {
setTSOLink(cap, tso->block_info.prev, tso->_link);
}
if (tso->_link == END_TSO_QUEUE) {
ASSERT(cap->run_queue_tl == tso);
cap->run_queue_tl = tso->block_info.prev;
} else {
setTSOPrev(cap, tso->_link, tso->block_info.prev);
}
tso->_link = tso->block_info.prev = END_TSO_QUEUE;
IF_DEBUG(sanity, checkRunQueue(cap));
}
void
promoteInRunQueue (Capability *cap, StgTSO *tso)
{
removeFromRunQueue(cap, tso);
pushOnRunQueue(cap, tso);
}
/* ----------------------------------------------------------------------------
* Setting up the scheduler loop
* ------------------------------------------------------------------------- */
static void
schedulePreLoop(void)
{
// initialisation for scheduler - what cannot go into initScheduler()
#if defined(mingw32_HOST_OS) && !defined(USE_MINIINTERPRETER)
win32AllocStack();
#endif
}
/* -----------------------------------------------------------------------------
* scheduleFindWork()
*
* Search for work to do, and handle messages from elsewhere.
* -------------------------------------------------------------------------- */
static void
scheduleFindWork (Capability **pcap)
{
scheduleStartSignalHandlers(*pcap);
scheduleProcessInbox(pcap);
scheduleCheckBlockedThreads(*pcap);
#if defined(THREADED_RTS)
if (emptyRunQueue(*pcap)) { scheduleActivateSpark(*pcap); }
#endif
}
#if defined(THREADED_RTS)
STATIC_INLINE rtsBool
shouldYieldCapability (Capability *cap, Task *task, rtsBool didGcLast)
{
// we need to yield this capability to someone else if..
// - another thread is initiating a GC, and we didn't just do a GC
// (see Note [GC livelock])
// - another Task is returning from a foreign call
// - the thread at the head of the run queue cannot be run
// by this Task (it is bound to another Task, or it is unbound
// and this task it bound).
//
// Note [GC livelock]
//
// If we are interrupted to do a GC, then we do not immediately do
// another one. This avoids a starvation situation where one
// Capability keeps forcing a GC and the other Capabilities make no
// progress at all.
return ((pending_sync && !didGcLast) ||
cap->returning_tasks_hd != NULL ||
(!emptyRunQueue(cap) && (task->incall->tso == NULL
? peekRunQueue(cap)->bound != NULL
: peekRunQueue(cap)->bound != task->incall)));
}
// This is the single place where a Task goes to sleep. There are
// two reasons it might need to sleep:
// - there are no threads to run
// - we need to yield this Capability to someone else
// (see shouldYieldCapability())
//
// Careful: the scheduler loop is quite delicate. Make sure you run
// the tests in testsuite/concurrent (all ways) after modifying this,
// and also check the benchmarks in nofib/parallel for regressions.
static void
scheduleYield (Capability **pcap, Task *task)
{
Capability *cap = *pcap;
int didGcLast = rtsFalse;
// if we have work, and we don't need to give up the Capability, continue.
//
if (!shouldYieldCapability(cap,task,rtsFalse) &&
(!emptyRunQueue(cap) ||
!emptyInbox(cap) ||
sched_state >= SCHED_INTERRUPTING)) {
return;
}
// otherwise yield (sleep), and keep yielding if necessary.
do {
didGcLast = yieldCapability(&cap,task, !didGcLast);
}
while (shouldYieldCapability(cap,task,didGcLast));
// note there may still be no threads on the run queue at this
// point, the caller has to check.
*pcap = cap;
return;
}
#endif
/* -----------------------------------------------------------------------------
* schedulePushWork()
*
* Push work to other Capabilities if we have some.
* -------------------------------------------------------------------------- */
static void
schedulePushWork(Capability *cap USED_IF_THREADS,
Task *task USED_IF_THREADS)
{
/* following code not for PARALLEL_HASKELL. I kept the call general,
future GUM versions might use pushing in a distributed setup */
#if defined(THREADED_RTS)
Capability *free_caps[n_capabilities], *cap0;
nat i, n_free_caps;
// migration can be turned off with +RTS -qm
if (!RtsFlags.ParFlags.migrate) return;
// Check whether we have more threads on our run queue, or sparks
// in our pool, that we could hand to another Capability.
if (emptyRunQueue(cap)) {
if (sparkPoolSizeCap(cap) < 2) return;
} else {
if (singletonRunQueue(cap) &&
sparkPoolSizeCap(cap) < 1) return;
}
// First grab as many free Capabilities as we can.
for (i=0, n_free_caps=0; i < n_capabilities; i++) {
cap0 = capabilities[i];
if (cap != cap0 && !cap0->disabled && tryGrabCapability(cap0,task)) {
if (!emptyRunQueue(cap0)
|| cap0->returning_tasks_hd != NULL
|| cap0->inbox != (Message*)END_TSO_QUEUE) {
// it already has some work, we just grabbed it at
// the wrong moment. Or maybe it's deadlocked!
releaseCapability(cap0);
} else {
free_caps[n_free_caps++] = cap0;
}
}
}
// we now have n_free_caps free capabilities stashed in
// free_caps[]. Share our run queue equally with them. This is
// probably the simplest thing we could do; improvements we might
// want to do include:
//
// - giving high priority to moving relatively new threads, on
// the gournds that they haven't had time to build up a
// working set in the cache on this CPU/Capability.
//
// - giving low priority to moving long-lived threads
if (n_free_caps > 0) {
StgTSO *prev, *t, *next;
#ifdef SPARK_PUSHING
rtsBool pushed_to_all;
#endif
debugTrace(DEBUG_sched,
"cap %d: %s and %d free capabilities, sharing...",
cap->no,
(!emptyRunQueue(cap) && !singletonRunQueue(cap))?
"excess threads on run queue":"sparks to share (>=2)",
n_free_caps);
i = 0;
#ifdef SPARK_PUSHING
pushed_to_all = rtsFalse;
#endif
if (cap->run_queue_hd != END_TSO_QUEUE) {
prev = cap->run_queue_hd;
t = prev->_link;
prev->_link = END_TSO_QUEUE;
for (; t != END_TSO_QUEUE; t = next) {
next = t->_link;
t->_link = END_TSO_QUEUE;
if (t->bound == task->incall // don't move my bound thread
|| tsoLocked(t)) { // don't move a locked thread
setTSOLink(cap, prev, t);
setTSOPrev(cap, t, prev);
prev = t;
} else if (i == n_free_caps) {
#ifdef SPARK_PUSHING
pushed_to_all = rtsTrue;
#endif
i = 0;
// keep one for us
setTSOLink(cap, prev, t);
setTSOPrev(cap, t, prev);
prev = t;
} else {
appendToRunQueue(free_caps[i],t);
traceEventMigrateThread (cap, t, free_caps[i]->no);
if (t->bound) { t->bound->task->cap = free_caps[i]; }
t->cap = free_caps[i];
i++;
}
}
cap->run_queue_tl = prev;
IF_DEBUG(sanity, checkRunQueue(cap));
}
#ifdef SPARK_PUSHING
/* JB I left this code in place, it would work but is not necessary */
// If there are some free capabilities that we didn't push any
// threads to, then try to push a spark to each one.
if (!pushed_to_all) {
StgClosure *spark;
// i is the next free capability to push to
for (; i < n_free_caps; i++) {
if (emptySparkPoolCap(free_caps[i])) {
spark = tryStealSpark(cap->sparks);
if (spark != NULL) {
/* TODO: if anyone wants to re-enable this code then
* they must consider the fizzledSpark(spark) case
* and update the per-cap spark statistics.
*/
debugTrace(DEBUG_sched, "pushing spark %p to capability %d", spark, free_caps[i]->no);
traceEventStealSpark(free_caps[i], t, cap->no);
newSpark(&(free_caps[i]->r), spark);
}
}
}
}
#endif /* SPARK_PUSHING */
// release the capabilities
for (i = 0; i < n_free_caps; i++) {
task->cap = free_caps[i];
releaseAndWakeupCapability(free_caps[i]);
}
}
task->cap = cap; // reset to point to our Capability.
#endif /* THREADED_RTS */
}
/* ----------------------------------------------------------------------------
* Start any pending signal handlers
* ------------------------------------------------------------------------- */
#if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
static void
scheduleStartSignalHandlers(Capability *cap)
{
if (RtsFlags.MiscFlags.install_signal_handlers && signals_pending()) {
// safe outside the lock
startSignalHandlers(cap);
}
}
#else
static void
scheduleStartSignalHandlers(Capability *cap STG_UNUSED)
{
}
#endif
/* ----------------------------------------------------------------------------
* Check for blocked threads that can be woken up.
* ------------------------------------------------------------------------- */
static void
scheduleCheckBlockedThreads(Capability *cap USED_IF_NOT_THREADS)
{
#if !defined(THREADED_RTS)
//
// Check whether any waiting threads need to be woken up. If the
// run queue is empty, and there are no other tasks running, we
// can wait indefinitely for something to happen.
//
if ( !emptyQueue(blocked_queue_hd) || !emptyQueue(sleeping_queue) )
{
awaitEvent (emptyRunQueue(cap));
}
#endif
}
/* ----------------------------------------------------------------------------
* Detect deadlock conditions and attempt to resolve them.
* ------------------------------------------------------------------------- */
static void
scheduleDetectDeadlock (Capability **pcap, Task *task)
{
Capability *cap = *pcap;
/*
* Detect deadlock: when we have no threads to run, there are no
* threads blocked, waiting for I/O, or sleeping, and all the
* other tasks are waiting for work, we must have a deadlock of
* some description.
*/
if ( emptyThreadQueues(cap) )
{
#if defined(THREADED_RTS)
/*
* In the threaded RTS, we only check for deadlock if there
* has been no activity in a complete timeslice. This means
* we won't eagerly start a full GC just because we don't have
* any threads to run currently.
*/
if (recent_activity != ACTIVITY_INACTIVE) return;
#endif
debugTrace(DEBUG_sched, "deadlocked, forcing major GC...");
// Garbage collection can release some new threads due to
// either (a) finalizers or (b) threads resurrected because
// they are unreachable and will therefore be sent an
// exception. Any threads thus released will be immediately
// runnable.
scheduleDoGC (pcap, task, rtsTrue/*force major GC*/);
cap = *pcap;
// when force_major == rtsTrue. scheduleDoGC sets
// recent_activity to ACTIVITY_DONE_GC and turns off the timer
// signal.
if ( !emptyRunQueue(cap) ) return;
#if defined(RTS_USER_SIGNALS) && !defined(THREADED_RTS)
/* If we have user-installed signal handlers, then wait
* for signals to arrive rather then bombing out with a
* deadlock.
*/
if ( RtsFlags.MiscFlags.install_signal_handlers && anyUserHandlers() ) {
debugTrace(DEBUG_sched,
"still deadlocked, waiting for signals...");
awaitUserSignals();
if (signals_pending()) {
startSignalHandlers(cap);
}
// either we have threads to run, or we were interrupted:
ASSERT(!emptyRunQueue(cap) || sched_state >= SCHED_INTERRUPTING);
return;
}
#endif
#if !defined(THREADED_RTS)
/* Probably a real deadlock. Send the current main thread the
* Deadlock exception.
*/
if (task->incall->tso) {
switch (task->incall->tso->why_blocked) {
case BlockedOnSTM:
case BlockedOnBlackHole:
case BlockedOnMsgThrowTo:
case BlockedOnMVar:
case BlockedOnMVarRead:
throwToSingleThreaded(cap, task->incall->tso,
(StgClosure *)nonTermination_closure);
return;
default:
barf("deadlock: main thread blocked in a strange way");
}
}
return;
#endif
}
}
/* ----------------------------------------------------------------------------
* Send pending messages (PARALLEL_HASKELL only)
* ------------------------------------------------------------------------- */
#if defined(PARALLEL_HASKELL)
static void
scheduleSendPendingMessages(void)
{
# if defined(PAR) // global Mem.Mgmt., omit for now
if (PendingFetches != END_BF_QUEUE) {
processFetches();
}
# endif
if (RtsFlags.ParFlags.BufferTime) {
// if we use message buffering, we must send away all message
// packets which have become too old...
sendOldBuffers();
}
}
#endif
/* ----------------------------------------------------------------------------
* Process message in the current Capability's inbox
* ------------------------------------------------------------------------- */
static void
scheduleProcessInbox (Capability **pcap USED_IF_THREADS)
{
#if defined(THREADED_RTS)
Message *m, *next;
int r;
Capability *cap = *pcap;
while (!emptyInbox(cap)) {
if (cap->r.rCurrentNursery->link == NULL ||