summaryrefslogtreecommitdiff
path: root/rts/Messages.c
blob: d4a51f4ea693ee0394416ca7028dbaead83ef6be (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
/* ---------------------------------------------------------------------------
 *
 * (c) The GHC Team, 2010
 *
 * Inter-Capability message passing
 *
 * --------------------------------------------------------------------------*/

#include "Rts.h"
#include "Messages.h"
#include "Trace.h"
#include "Capability.h"
#include "Schedule.h"
#include "Threads.h"
#include "RaiseAsync.h"
#include "sm/Storage.h"
#include "CloneStack.h"

/* ----------------------------------------------------------------------------
   Send a message to another Capability
   ------------------------------------------------------------------------- */

#if defined(THREADED_RTS)

void sendMessage(Capability *from_cap, Capability *to_cap, Message *msg)
{
    ACQUIRE_LOCK(&to_cap->lock);

#if defined(DEBUG)
    {
        const StgInfoTable *i = msg->header.info;
        if (i != &stg_MSG_THROWTO_info &&
            i != &stg_MSG_BLACKHOLE_info &&
            i != &stg_MSG_TRY_WAKEUP_info &&
            i != &stg_IND_info && // can happen if a MSG_BLACKHOLE is revoked
            i != &stg_WHITEHOLE_info &&
            i != &stg_MSG_CLONE_STACK_info) {
            barf("sendMessage: %p", i);
        }
    }
#endif

    msg->link = to_cap->inbox;
    RELAXED_STORE(&to_cap->inbox, msg);

    recordClosureMutated(from_cap,(StgClosure*)msg);

    if (to_cap->running_task == NULL) {
        to_cap->running_task = myTask();
            // precond for releaseCapability_()
        releaseCapability_(to_cap,false);
    } else {
        interruptCapability(to_cap);
    }

    RELEASE_LOCK(&to_cap->lock);
}

#endif /* THREADED_RTS */

/* ----------------------------------------------------------------------------
   Handle a message
   ------------------------------------------------------------------------- */

#if defined(THREADED_RTS)

void
executeMessage (Capability *cap, Message *m)
{
    const StgInfoTable *i;

loop:
    i = ACQUIRE_LOAD(&m->header.info);
    if (i == &stg_MSG_TRY_WAKEUP_info)
    {
        StgTSO *tso = ((MessageWakeup *)m)->tso;
        debugTraceCap(DEBUG_sched, cap, "message: try wakeup thread %"
                      FMT_StgThreadID, tso->id);
        tryWakeupThread(cap, tso);
    }
    else if (i == &stg_MSG_THROWTO_info)
    {
        MessageThrowTo *t = (MessageThrowTo *)m;
        uint32_t 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",
                      (W_)t->source->id, (W_)t->target->id);

        r = throwToMsg(cap, t);

        switch (r) {
        case THROWTO_SUCCESS: {
            // this message is done
            StgTSO *source = t->source;
            doneWithMsgThrowTo(cap, 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)
    {
        uint32_t 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)
    {
#if defined(PROF_SPIN)
        NONATOMIC_ADD(&whitehole_executeMessage_spin, 1);
#endif
        goto loop;
    }
    else if(i == &stg_MSG_CLONE_STACK_info){
        MessageCloneStack *cloneStackMessage = (MessageCloneStack*) m;
        handleCloneStackMessage(cloneStackMessage);
    }
    else
    {
        barf("executeMessage: %p", i);
    }
}

#endif

/* ----------------------------------------------------------------------------
   Handle a MSG_BLACKHOLE message

   This is called from two places: either we just entered a BLACKHOLE
   (stg_BLACKHOLE_info), or we received a MSG_BLACKHOLE in our
   cap->inbox.

   We need to establish whether the BLACKHOLE belongs to
   this Capability, and
     - if so, arrange to block the current thread on it
     - otherwise, forward the message to the right place

   Returns:
     - 0 if the blocked thread can be woken up by the caller
     - 1 if the thread is still blocked, and we promise to send a MSG_TRY_WAKEUP
       at some point in the future.

   ------------------------------------------------------------------------- */

uint32_t 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 %" FMT_StgThreadID
                  " blocking on blackhole %p", msg->tso->id, msg->bh);

    info = ACQUIRE_LOAD(&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:
    // If we are being called from stg_BLACKHOLE then TSAN won't know about the
    // previous read barrier that makes the following access safe.
    TSAN_ANNOTATE_BENIGN_RACE(&((StgInd*)bh)->indirectee, "messageBlackHole");
    p = UNTAG_CLOSURE(ACQUIRE_LOAD(&((StgInd*)bh)->indirectee));
    info = RELAXED_LOAD(&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.
        // See Note [BLACKHOLE pointing to IND] in sm/Evac.c
        goto loop;
    }

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

#if defined(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
        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;
        SET_HDR(bq, &stg_BLOCKING_QUEUE_DIRTY_info, CCS_SYSTEM);
        // We are about to make the newly-constructed message visible to other cores;
        // a barrier is necessary to ensure that all writes are visible.
        // See Note [Heap memory barriers] in SMP.h.
        dirty_TSO(cap, owner); // we will modify owner->bq
        RELEASE_STORE(&owner->bq, 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) {
            promoteInRunQueue(cap, owner);
        }

        // point to the BLOCKING_QUEUE from the BLACKHOLE
        // RELEASE to make the BQ visible, see Note [Heap memory barriers].
        RELEASE_STORE(&((StgInd*)bh)->indirectee, (StgClosure *)bq);
        IF_NONMOVING_WRITE_BARRIER_ENABLED {
            updateRemembSetPushClosure(cap, (StgClosure*)p);
        }
        recordClosureMutated(cap,bh); // bh was mutated

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

#if defined(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

        IF_NONMOVING_WRITE_BARRIER_ENABLED {
            // We are about to overwrite bq->queue; make sure its current value
            // makes it into the update remembered set
            updateRemembSetPushClosure(cap, (StgClosure*)bq->queue);
        }
        RELAXED_STORE(&msg->link, bq->queue);
        bq->queue = msg;
        // No barrier is necessary here: we are only exposing the
        // closure to the GC. See Note [Heap memory barriers] in SMP.h.
        recordClosureMutated(cap,(StgClosure*)msg);

        if (info == &stg_BLOCKING_QUEUE_CLEAN_info) {
            RELAXED_STORE(&bq->header.info, &stg_BLOCKING_QUEUE_DIRTY_info);
            // No barrier is necessary here: we are only exposing the
            // closure to the GC. See Note [Heap memory barriers] in SMP.h.
            recordClosureMutated(cap,(StgClosure*)bq);
        }

        debugTraceCap(DEBUG_sched, cap,
                      "thread %" FMT_StgThreadID " blocked on existing "
                      "BLOCKING_QUEUE owned by thread %" FMT_StgThreadID,
                      msg->tso->id, owner->id);

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

        return 1; // blocked
    }

    return 0; // not blocked
}

// A shorter version of messageBlackHole(), that just returns the
// owner (or NULL if the owner cannot be found, because the blackhole
// has been updated in the meantime).

StgTSO * blackHoleOwner (StgClosure *bh)
{
    const StgInfoTable *info;
    StgClosure *p;

    info = RELAXED_LOAD(&bh->header.info);

    if (info != &stg_BLACKHOLE_info &&
        info != &stg_CAF_BLACKHOLE_info &&
        info != &__stg_EAGER_BLACKHOLE_info &&
        info != &stg_WHITEHOLE_info) {
        return NULL;
    }

    // The blackhole must indirect to a TSO, a BLOCKING_QUEUE, an IND,
    // or a value.
loop:
    p = UNTAG_CLOSURE(ACQUIRE_LOAD(&((StgInd*)bh)->indirectee));
    info = RELAXED_LOAD(&p->header.info);

    if (info == &stg_IND_info) goto loop;

    else if (info == &stg_TSO_info)
    {
        return (StgTSO*)p;
    }
    else if (info == &stg_BLOCKING_QUEUE_CLEAN_info ||
             info == &stg_BLOCKING_QUEUE_DIRTY_info)
    {
        StgBlockingQueue *bq = (StgBlockingQueue *)p;
        return RELAXED_LOAD(&bq->owner);
    }

    return NULL; // not blocked
}