Example #1
0
// If we update a closure that we know we BLACKHOLE'd, and the closure
// no longer points to the current TSO as its owner, then there may be
// an orphaned BLOCKING_QUEUE closure with blocked threads attached to
// it.  We therefore traverse the BLOCKING_QUEUEs attached to the
// current TSO to see if any can now be woken up.
void
checkBlockingQueues (Capability *cap, StgTSO *tso)
{
    StgBlockingQueue *bq, *next;
    StgClosure *p;

    debugTraceCap(DEBUG_sched, cap,
                  "collision occurred; checking blocking queues for thread %ld",
                  (W_)tso->id);

    for (bq = tso->bq; bq != (StgBlockingQueue*)END_TSO_QUEUE; bq = next) {
        next = bq->link;

        if (bq->header.info == &stg_IND_info) {
            // ToDo: could short it out right here, to avoid
            // traversing this IND multiple times.
            continue;
        }

        p = bq->bh;

        if (p->header.info != &stg_BLACKHOLE_info ||
            ((StgInd *)p)->indirectee != (StgClosure*)bq)
        {
            wakeBlockingQueue(cap,bq);
        }
    }
}
Example #2
0
nat
throwToMsg (Capability *cap, MessageThrowTo *msg)
{
    StgWord status;
    StgTSO *target = msg->target;
    Capability *target_cap;

    goto check_target;

retry:
    write_barrier();
    debugTrace(DEBUG_sched, "throwTo: retrying...");

check_target:
    ASSERT(target != END_TSO_QUEUE);

    // Thread already dead?
    if (target->what_next == ThreadComplete
        || target->what_next == ThreadKilled) {
        return THROWTO_SUCCESS;
    }

    debugTraceCap(DEBUG_sched, cap,
                  "throwTo: from thread %lu to thread %lu",
                  (unsigned long)msg->source->id,
                  (unsigned long)msg->target->id);

#ifdef DEBUG
    traceThreadStatus(DEBUG_sched, target);
#endif

    target_cap = target->cap;
    if (target->cap != cap) {
        throwToSendMsg(cap, target_cap, msg);
        return THROWTO_BLOCKED;
    }

    status = target->why_blocked;

    switch (status) {
    case NotBlocked:
    {
        if ((target->flags & TSO_BLOCKEX) == 0) {
            // It's on our run queue and not blocking exceptions
            raiseAsync(cap, target, msg->exception, rtsFalse, NULL);
            return THROWTO_SUCCESS;
        } else {
            blockedThrowTo(cap,target,msg);
            return THROWTO_BLOCKED;
        }
    }

    case BlockedOnMsgThrowTo:
    {
        const StgInfoTable *i;
        MessageThrowTo *m;

        m = target->block_info.throwto;

        // target is local to this cap, but has sent a throwto
        // message to another cap.
        //
        // The source message is locked.  We need to revoke the
        // target's message so that we can raise the exception, so
        // we attempt to lock it.

        // There's a possibility of a deadlock if two threads are both
        // trying to throwTo each other (or more generally, a cycle of
        // threads).  To break the symmetry we compare the addresses
        // of the MessageThrowTo objects, and the one for which m <
        // msg gets to spin, while the other can only try to lock
        // once, but must then back off and unlock both before trying
        // again.
        if (m < msg) {
            i = lockClosure((StgClosure *)m);
        } else {
            i = tryLockClosure((StgClosure *)m);
            if (i == NULL) {
//            debugBelch("collision\n");
                throwToSendMsg(cap, target->cap, msg);
                return THROWTO_BLOCKED;
            }
        }

        if (i == &stg_MSG_NULL_info) {
            // we know there's a MSG_TRY_WAKEUP on the way, so we
            // might as well just do it now.  The message will
            // be a no-op when it arrives.
            unlockClosure((StgClosure*)m, i);
            tryWakeupThread(cap, target);
            goto retry;
        }

        if (i != &stg_MSG_THROWTO_info) {
            // if it's a MSG_NULL, this TSO has been woken up by another Cap
            unlockClosure((StgClosure*)m, i);
            goto retry;
        }

        if ((target->flags & TSO_BLOCKEX) &&
            ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
            unlockClosure((StgClosure*)m, i);
            blockedThrowTo(cap,target,msg);
            return THROWTO_BLOCKED;
        }

        // nobody else can wake up this TSO after we claim the message
        doneWithMsgThrowTo(m);

        raiseAsync(cap, target, msg->exception, rtsFalse, NULL);
        return THROWTO_SUCCESS;
    }

    case BlockedOnMVar:
    case BlockedOnMVarRead:
    {
        /*
          To establish ownership of this TSO, we need to acquire a
          lock on the MVar that it is blocked on.
        */
        StgMVar *mvar;
        StgInfoTable *info USED_IF_THREADS;

        mvar = (StgMVar *)target->block_info.closure;

        // ASSUMPTION: tso->block_info must always point to a
        // closure.  In the threaded RTS it does.
        switch (get_itbl((StgClosure *)mvar)->type) {
        case MVAR_CLEAN:
        case MVAR_DIRTY:
            break;
        default:
            goto retry;
        }

        info = lockClosure((StgClosure *)mvar);

        // we have the MVar, let's check whether the thread
        // is still blocked on the same MVar.
        if ((target->why_blocked != BlockedOnMVar && target->why_blocked != BlockedOnMVarRead)
            || (StgMVar *)target->block_info.closure != mvar) {
            unlockClosure((StgClosure *)mvar, info);
            goto retry;
        }

        if (target->_link == END_TSO_QUEUE) {
            // the MVar operation has already completed.  There is a
            // MSG_TRY_WAKEUP on the way, but we can just wake up the
            // thread now anyway and ignore the message when it
            // arrives.
            unlockClosure((StgClosure *)mvar, info);
            tryWakeupThread(cap, target);
            goto retry;
        }

        if ((target->flags & TSO_BLOCKEX) &&
            ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
            blockedThrowTo(cap,target,msg);
            unlockClosure((StgClosure *)mvar, info);
            return THROWTO_BLOCKED;
        } else {
            // revoke the MVar operation
            removeFromMVarBlockedQueue(target);
            raiseAsync(cap, target, msg->exception, rtsFalse, NULL);
            unlockClosure((StgClosure *)mvar, info);
            return THROWTO_SUCCESS;
        }
    }

    case BlockedOnBlackHole:
    {
        if (target->flags & TSO_BLOCKEX) {
            // BlockedOnBlackHole is not interruptible.
            blockedThrowTo(cap,target,msg);
            return THROWTO_BLOCKED;
        } else {
            // Revoke the message by replacing it with IND. We're not
            // locking anything here, so we might still get a TRY_WAKEUP
            // message from the owner of the blackhole some time in the
            // future, but that doesn't matter.
            ASSERT(target->block_info.bh->header.info == &stg_MSG_BLACKHOLE_info);
            OVERWRITE_INFO(target->block_info.bh, &stg_IND_info);
            raiseAsync(cap, target, msg->exception, rtsFalse, NULL);
            return THROWTO_SUCCESS;
        }
    }

    case BlockedOnSTM:
        lockTSO(target);
        // Unblocking BlockedOnSTM threads requires the TSO to be
        // locked; see STM.c:unpark_tso().
        if (target->why_blocked != BlockedOnSTM) {
            unlockTSO(target);
            goto retry;
        }
        if ((target->flags & TSO_BLOCKEX) &&
            ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
            blockedThrowTo(cap,target,msg);
            unlockTSO(target);
            return THROWTO_BLOCKED;
        } else {
            raiseAsync(cap, target, msg->exception, rtsFalse, NULL);
            unlockTSO(target);
            return THROWTO_SUCCESS;
        }

    case BlockedOnCCall_Interruptible:
#ifdef THREADED_RTS
    {
        Task *task = NULL;
        // walk suspended_ccalls to find the correct worker thread
        InCall *incall;
        for (incall = cap->suspended_ccalls; incall != NULL; incall = incall->next) {
            if (incall->suspended_tso == target) {
                task = incall->task;
                break;
            }
        }
        if (task != NULL) {
            blockedThrowTo(cap, target, msg);
            if (!((target->flags & TSO_BLOCKEX) &&
                  ((target->flags & TSO_INTERRUPTIBLE) == 0))) {
                interruptWorkerTask(task);
            }
            return THROWTO_BLOCKED;
        } else {
            debugTraceCap(DEBUG_sched, cap, "throwTo: could not find worker thread to kill");
        }
        // fall to next
    }
#endif
    case BlockedOnCCall:
        blockedThrowTo(cap,target,msg);
        return THROWTO_BLOCKED;

#ifndef THREADEDED_RTS
    case BlockedOnRead:
    case BlockedOnWrite:
    case BlockedOnDelay:
#if defined(mingw32_HOST_OS)
    case BlockedOnDoProc:
#endif
        if ((target->flags & TSO_BLOCKEX) &&
            ((target->flags & TSO_INTERRUPTIBLE) == 0)) {
            blockedThrowTo(cap,target,msg);
            return THROWTO_BLOCKED;
        } else {
            removeFromQueues(cap,target);
            raiseAsync(cap, target, msg->exception, rtsFalse, NULL);
            return THROWTO_SUCCESS;
        }
#endif

    case ThreadMigrating:
        // if is is ThreadMigrating and tso->cap is ours, then it
        // *must* be migrating *to* this capability.  If it were
        // migrating away from the capability, then tso->cap would
        // point to the destination.
        //
        // There is a MSG_WAKEUP in the message queue for this thread,
        // but we can just do it preemptively:
        tryWakeupThread(cap, target);
        // and now retry, the thread should be runnable.
        goto retry;

    default:
        barf("throwTo: unrecognised why_blocked (%d)", target->why_blocked);
    }
    barf("throwTo");
}
Example #3
0
void
executeMessage (Capability *cap, Message *m)
{
    const StgInfoTable *i;

loop:
    write_barrier(); // allow m->header to be modified by another thread
    i = m->header.info;
    if (i == &stg_MSG_TRY_WAKEUP_info)
    {
        StgTSO *tso = ((MessageWakeup *)m)->tso;
        debugTraceCap(DEBUG_sched, cap, "message: try wakeup thread %ld", 
                      (lnat)tso->id);
        tryWakeupThread(cap, tso);
    }
    else if (i == &stg_MSG_THROWTO_info)
    {
        MessageThrowTo *t = (MessageThrowTo *)m;
        nat r;
        const StgInfoTable *i;

        i = lockClosure((StgClosure*)m);
        if (i != &stg_MSG_THROWTO_info) {
            unlockClosure((StgClosure*)m, i);
            goto loop;
        }

        debugTraceCap(DEBUG_sched, cap, "message: throwTo %ld -> %ld", 
                      (lnat)t->source->id, (lnat)t->target->id);

        ASSERT(t->source->why_blocked == BlockedOnMsgThrowTo);
        ASSERT(t->source->block_info.closure == (StgClosure *)m);

        r = throwToMsg(cap, t);

        switch (r) {
        case THROWTO_SUCCESS: {
            // this message is done
            StgTSO *source = t->source;
            doneWithMsgThrowTo(t);
            tryWakeupThread(cap, source);
            break;
        }
        case THROWTO_BLOCKED:
            // unlock the message
            unlockClosure((StgClosure*)m, &stg_MSG_THROWTO_info);
            break;
        }
    }
    else if (i == &stg_MSG_BLACKHOLE_info)
    {
        nat r;
        MessageBlackHole *b = (MessageBlackHole*)m;

        r = messageBlackHole(cap, b);
        if (r == 0) {
            tryWakeupThread(cap, b->tso);
        }
        return;
    }
    else if (i == &stg_IND_info || i == &stg_MSG_NULL_info)
    {
        // message was revoked
        return;
    }
    else if (i == &stg_WHITEHOLE_info)
    {
        goto loop;
    }
    else
    {
        barf("executeMessage: %p", i);
    }
}
Example #4
0
nat messageBlackHole(Capability *cap, MessageBlackHole *msg)
{
    const StgInfoTable *info;
    StgClosure *p;
    StgBlockingQueue *bq;
    StgClosure *bh = UNTAG_CLOSURE(msg->bh);
    StgTSO *owner;

    debugTraceCap(DEBUG_sched, cap, "message: thread %d blocking on blackhole %p", 
                  (lnat)msg->tso->id, msg->bh);

    info = bh->header.info;

    // If we got this message in our inbox, it might be that the
    // BLACKHOLE has already been updated, and GC has shorted out the
    // indirection, so the pointer no longer points to a BLACKHOLE at
    // all.
    if (info != &stg_BLACKHOLE_info && 
        info != &stg_CAF_BLACKHOLE_info && 
        info != &__stg_EAGER_BLACKHOLE_info &&
        info != &stg_WHITEHOLE_info) {
        // if it is a WHITEHOLE, then a thread is in the process of
        // trying to BLACKHOLE it.  But we know that it was once a
        // BLACKHOLE, so there is at least a valid pointer in the
        // payload, so we can carry on.
        return 0;
    }

    // The blackhole must indirect to a TSO, a BLOCKING_QUEUE, an IND,
    // or a value.
loop:
    // NB. VOLATILE_LOAD(), because otherwise gcc hoists the load
    // and turns this into an infinite loop.
    p = UNTAG_CLOSURE((StgClosure*)VOLATILE_LOAD(&((StgInd*)bh)->indirectee));
    info = p->header.info;

    if (info == &stg_IND_info)
    {
        // This could happen, if e.g. we got a BLOCKING_QUEUE that has
        // just been replaced with an IND by another thread in
        // updateThunk().  In which case, if we read the indirectee
        // again we should get the value.
        goto loop;
    }

    else if (info == &stg_TSO_info)
    {
        owner = (StgTSO*)p;

#ifdef THREADED_RTS
        if (owner->cap != cap) {
            sendMessage(cap, owner->cap, (Message*)msg);
            debugTraceCap(DEBUG_sched, cap, "forwarding message to cap %d", owner->cap->no);
            return 1;
        }
#endif
        // owner is the owner of the BLACKHOLE, and resides on this
        // Capability.  msg->tso is the first thread to block on this
        // BLACKHOLE, so we first create a BLOCKING_QUEUE object.

        bq = (StgBlockingQueue*)allocate(cap, sizeofW(StgBlockingQueue));
            
        // initialise the BLOCKING_QUEUE object
        SET_HDR(bq, &stg_BLOCKING_QUEUE_DIRTY_info, CCS_SYSTEM);
        bq->bh = bh;
        bq->queue = msg;
        bq->owner = owner;
        
        msg->link = (MessageBlackHole*)END_TSO_QUEUE;
        
        // All BLOCKING_QUEUES are linked in a list on owner->bq, so
        // that we can search through them in the event that there is
        // a collision to update a BLACKHOLE and a BLOCKING_QUEUE
        // becomes orphaned (see updateThunk()).
        bq->link = owner->bq;
        owner->bq = bq;
        dirty_TSO(cap, owner); // we modified owner->bq

        // If the owner of the blackhole is currently runnable, then
        // bump it to the front of the run queue.  This gives the
        // blocked-on thread a little boost which should help unblock
        // this thread, and may avoid a pile-up of other threads
        // becoming blocked on the same BLACKHOLE (#3838).
        //
        // NB. we check to make sure that the owner is not the same as
        // the current thread, since in that case it will not be on
        // the run queue.
        if (owner->why_blocked == NotBlocked && owner->id != msg->tso->id) {
            removeFromRunQueue(cap, owner);
            pushOnRunQueue(cap,owner);
        }

        // point to the BLOCKING_QUEUE from the BLACKHOLE
        write_barrier(); // make the BQ visible
        ((StgInd*)bh)->indirectee = (StgClosure *)bq;
        recordClosureMutated(cap,bh); // bh was mutated

        debugTraceCap(DEBUG_sched, cap, "thread %d blocked on thread %d", 
                      (lnat)msg->tso->id, (lnat)owner->id);

        return 1; // blocked
    }
    else if (info == &stg_BLOCKING_QUEUE_CLEAN_info || 
             info == &stg_BLOCKING_QUEUE_DIRTY_info)
    {
        StgBlockingQueue *bq = (StgBlockingQueue *)p;

        ASSERT(bq->bh == bh);

        owner = bq->owner;

        ASSERT(owner != END_TSO_QUEUE);

#ifdef THREADED_RTS
        if (owner->cap != cap) {
            sendMessage(cap, owner->cap, (Message*)msg);
            debugTraceCap(DEBUG_sched, cap, "forwarding message to cap %d", owner->cap->no);
            return 1;
        }
#endif

        msg->link = bq->queue;
        bq->queue = msg;
        recordClosureMutated(cap,(StgClosure*)msg);

        if (info == &stg_BLOCKING_QUEUE_CLEAN_info) {
            bq->header.info = &stg_BLOCKING_QUEUE_DIRTY_info;
            recordClosureMutated(cap,(StgClosure*)bq);
        }

        debugTraceCap(DEBUG_sched, cap, "thread %d blocked on thread %d", 
                      (lnat)msg->tso->id, (lnat)owner->id);

        // See above, #3838
        if (owner->why_blocked == NotBlocked && owner->id != msg->tso->id) {
            removeFromRunQueue(cap, owner);
            pushOnRunQueue(cap,owner);
        }

        return 1; // blocked
    }
    
    return 0; // not blocked
}
Example #5
0
void
tryWakeupThread (Capability *cap, StgTSO *tso)
{
    traceEventThreadWakeup (cap, tso, tso->cap->no);

#ifdef THREADED_RTS
    if (tso->cap != cap)
    {
        MessageWakeup *msg;
        msg = (MessageWakeup *)allocate(cap,sizeofW(MessageWakeup));
        SET_HDR(msg, &stg_MSG_TRY_WAKEUP_info, CCS_SYSTEM);
        msg->tso = tso;
        sendMessage(cap, tso->cap, (Message*)msg);
        debugTraceCap(DEBUG_sched, cap, "message: try wakeup thread %ld on cap %d",
                      (W_)tso->id, tso->cap->no);
        return;
    }
#endif

    switch (tso->why_blocked)
    {
    case BlockedOnMVar:
    case BlockedOnMVarRead:
    {
        if (tso->_link == END_TSO_QUEUE) {
            tso->block_info.closure = (StgClosure*)END_TSO_QUEUE;
            goto unblock;
        } else {
            return;
        }
    }

    case BlockedOnMsgThrowTo:
    {
        const StgInfoTable *i;

        i = lockClosure(tso->block_info.closure);
        unlockClosure(tso->block_info.closure, i);
        if (i != &stg_MSG_NULL_info) {
            debugTraceCap(DEBUG_sched, cap, "thread %ld still blocked on throwto (%p)",
                          (W_)tso->id, tso->block_info.throwto->header.info);
            return;
        }

        // remove the block frame from the stack
        ASSERT(tso->stackobj->sp[0] == (StgWord)&stg_block_throwto_info);
        tso->stackobj->sp += 3;
        goto unblock;
    }

    case BlockedOnBlackHole:
    case BlockedOnSTM:
    case ThreadMigrating:
        goto unblock;

    default:
        // otherwise, do nothing
        return;
    }

unblock:
    // just run the thread now, if the BH is not really available,
    // we'll block again.
    tso->why_blocked = NotBlocked;
    appendToRunQueue(cap,tso);

    // We used to set the context switch flag here, which would
    // trigger a context switch a short time in the future (at the end
    // of the current nursery block).  The idea is that we have just
    // woken up a thread, so we may need to load-balance and migrate
    // threads to other CPUs.  On the other hand, setting the context
    // switch flag here unfairly penalises the current thread by
    // yielding its time slice too early.
    //
    // The synthetic benchmark nofib/smp/chan can be used to show the
    // difference quite clearly.

    // cap->context_switch = 1;
}