1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team 1998-2005
10 * See the PPoPP 2005 paper "Composable memory transactions". In summary,
11 * each transcation has a TRec (transaction record) holding entries for each of the
12 * TVars (transactional variables) that it has accessed. Each entry records
13 * (a) the TVar, (b) the expected value seen in the TVar, (c) the new value that
14 * the transaction wants to write to the TVar, (d) during commit, the identity of
15 * the TRec that wrote the expected value.
17 * Separate TRecs are used for each level in a nest of transactions. This allows
18 * a nested transaction to be aborted without condemning its enclosing transactions.
19 * This is needed in the implementation of catchRetry. Note that the "expected value"
20 * in a nested transaction's TRec is the value expected to be *held in memory* if
21 * the transaction commits -- not the "new value" stored in one of the enclosing
22 * transactions. This means that validation can be done without searching through
28 * Three different concurrency control schemes can be built according to the settings
31 * STM_UNIPROC assumes that the caller serialises invocations on the STM interface.
32 * In the Haskell RTS this means it is suitable only for non-SMP builds.
34 * STM_CG_LOCK uses coarse-grained locking -- a single 'stm lock' is acquired during
35 * an invocation on the STM interface. Note that this does not mean that
36 * transactions are simply serialized -- the lock is only held *within* the
37 * implementation of stmCommitTransaction, stmWait etc.
39 * STM_FG_LOCKS uses fine-grained locking -- locking is done on a per-TVar basis
40 * and, when committing a transaction, no locks are acquired for TVars that have
41 * been read but not updated.
43 * Concurrency control is implemented in the functions:
47 * lock_tvar / cond_lock_tvar
50 * The choice between STM_UNIPROC / STM_CG_LOCK / STM_FG_LOCKS affects the
51 * implementation of these functions.
53 * lock_stm & unlock_stm are straightforward : they acquire a simple spin-lock
54 * using STM_CG_LOCK, and otherwise they are no-ops.
56 * lock_tvar / cond_lock_tvar and unlock_tvar are more complex because they
57 * have other effects (present in STM_UNIPROC and STM_CG_LOCK builds) as well
58 * as the actual business of maniupultaing a lock (present only in STM_FG_LOCKS
59 * builds). This is because locking a TVar is implemented by writing the lock
60 * holder's TRec into the TVar's current_value field:
62 * lock_tvar - lock a specified TVar (STM_FG_LOCKS only), returning the value
65 * cond_lock_tvar - lock a specified TVar (STM_FG_LOCKS only) if it
66 * contains a specified value. Return TRUE if this succeeds,
69 * unlock_tvar - release the lock on a specified TVar (STM_FG_LOCKS only),
70 * storing a specified value in place of the lock entry.
72 * Using these operations, the typcial pattern of a commit/validate/wait operation
73 * is to (a) lock the STM, (b) lock all the TVars being updated, (c) check that
74 * the TVars that were only read from still contain their expected values,
75 * (d) release the locks on the TVars, writing updates to them in the case of a
76 * commit, (e) unlock the STM.
78 * Queues of waiting threads hang off the first_wait_queue_entry field of each
79 * TVar. This may only be manipulated when holding that TVar's lock. In
80 * particular, when a thread is putting itself to sleep, it mustn't release
81 * the TVar's lock until it has added itself to the wait queue and marked its
82 * TSO as BlockedOnSTM -- this makes sure that other threads will know to wake it.
84 * ---------------------------------------------------------------------------*/
86 #include "PosixSource.h"
101 // ACQ_ASSERT is used for assertions which are only required for SMP builds with
102 // fine-grained locking.
104 #if defined(STM_FG_LOCKS)
105 #define ACQ_ASSERT(_X) ASSERT(_X)
106 #define NACQ_ASSERT(_X) /*Nothing*/
108 #define ACQ_ASSERT(_X) /*Nothing*/
109 #define NACQ_ASSERT(_X) ASSERT(_X)
112 /*......................................................................*/
114 // If SHAKE is defined then validation will sometime spuriously fail. They helps test
115 // unusualy code paths if genuine contention is rare
119 #define TRACE(_x...) IF_DEBUG(stm, debugBelch ( _x ))
121 #define TRACE(_x...) /*Nothing*/
125 static const int do_shake = TRUE;
127 static const int do_shake = FALSE;
129 static int shake_ctr = 0;
130 static int shake_lim = 1;
132 static int shake(void) {
134 if (((shake_ctr++) % shake_lim) == 0) {
145 /*......................................................................*/
147 // Helper macros for iterating over entries within a transaction
150 #define FOR_EACH_ENTRY(_t,_x,CODE) do { \
151 StgTRecHeader *__t = (_t); \
152 StgTRecChunk *__c = __t -> current_chunk; \
153 StgWord __limit = __c -> next_entry_idx; \
154 TRACE("%p : FOR_EACH_ENTRY, current_chunk=%p limit=%ld\n", __t, __c, __limit); \
155 while (__c != END_STM_CHUNK_LIST) { \
157 for (__i = 0; __i < __limit; __i ++) { \
158 TRecEntry *_x = &(__c -> entries[__i]); \
159 do { CODE } while (0); \
161 __c = __c -> prev_chunk; \
162 __limit = TREC_CHUNK_NUM_ENTRIES; \
165 if (FALSE) goto exit_for_each; \
168 #define BREAK_FOR_EACH goto exit_for_each
170 /*......................................................................*/
172 #define IF_STM_UNIPROC(__X) do { } while (0)
173 #define IF_STM_CG_LOCK(__X) do { } while (0)
174 #define IF_STM_FG_LOCKS(__X) do { } while (0)
176 #if defined(STM_UNIPROC)
177 #undef IF_STM_UNIPROC
178 #define IF_STM_UNIPROC(__X) do { __X } while (0)
179 static const StgBool use_read_phase = FALSE;
181 static void lock_stm(StgTRecHeader *trec STG_UNUSED) {
182 TRACE("%p : lock_stm()\n", trec);
185 static void unlock_stm(StgTRecHeader *trec STG_UNUSED) {
186 TRACE("%p : unlock_stm()\n", trec);
189 static StgClosure *lock_tvar(StgTRecHeader *trec STG_UNUSED,
190 StgTVar *s STG_UNUSED) {
192 TRACE("%p : lock_tvar(%p)\n", trec, s);
193 result = s -> current_value;
197 static void unlock_tvar(StgTRecHeader *trec STG_UNUSED,
198 StgTVar *s STG_UNUSED,
200 StgBool force_update) {
201 TRACE("%p : unlock_tvar(%p)\n", trec, s);
203 s -> current_value = c;
207 static StgBool cond_lock_tvar(StgTRecHeader *trec STG_UNUSED,
208 StgTVar *s STG_UNUSED,
209 StgClosure *expected) {
211 TRACE("%p : cond_lock_tvar(%p, %p)\n", trec, s, expected);
212 result = s -> current_value;
213 TRACE("%p : %s\n", trec, (result == expected) ? "success" : "failure");
214 return (result == expected);
218 #if defined(STM_CG_LOCK) /*........................................*/
220 #undef IF_STM_CG_LOCK
221 #define IF_STM_CG_LOCK(__X) do { __X } while (0)
222 static const StgBool use_read_phase = FALSE;
223 static volatile StgTRecHeader *smp_locked = NULL;
225 static void lock_stm(StgTRecHeader *trec) {
226 while (cas(&smp_locked, NULL, trec) != NULL) { }
227 TRACE("%p : lock_stm()\n", trec);
230 static void unlock_stm(StgTRecHeader *trec STG_UNUSED) {
231 TRACE("%p : unlock_stm()\n", trec);
232 ASSERT (smp_locked == trec);
236 static StgClosure *lock_tvar(StgTRecHeader *trec STG_UNUSED,
237 StgTVar *s STG_UNUSED) {
239 TRACE("%p : lock_tvar(%p)\n", trec, s);
240 ASSERT (smp_locked == trec);
241 result = s -> current_value;
245 static void *unlock_tvar(StgTRecHeader *trec STG_UNUSED,
246 StgTVar *s STG_UNUSED,
248 StgBool force_update) {
249 TRACE("%p : unlock_tvar(%p, %p)\n", trec, s, c);
250 ASSERT (smp_locked == trec);
252 s -> current_value = c;
256 static StgBool cond_lock_tvar(StgTRecHeader *trec STG_UNUSED,
257 StgTVar *s STG_UNUSED,
258 StgClosure *expected) {
260 TRACE("%p : cond_lock_tvar(%p, %p)\n", trec, s, expected);
261 ASSERT (smp_locked == trec);
262 result = s -> current_value;
263 TRACE("%p : %d\n", result ? "success" : "failure");
264 return (result == expected);
268 #if defined(STM_FG_LOCKS) /*...................................*/
270 #undef IF_STM_FG_LOCKS
271 #define IF_STM_FG_LOCKS(__X) do { __X } while (0)
272 static const StgBool use_read_phase = TRUE;
274 static void lock_stm(StgTRecHeader *trec STG_UNUSED) {
275 TRACE("%p : lock_stm()\n", trec);
278 static void unlock_stm(StgTRecHeader *trec STG_UNUSED) {
279 TRACE("%p : unlock_stm()\n", trec);
282 static StgClosure *lock_tvar(StgTRecHeader *trec,
283 StgTVar *s STG_UNUSED) {
285 TRACE("%p : lock_tvar(%p)\n", trec, s);
288 result = s -> current_value;
289 } while (GET_INFO(result) == &stg_TREC_HEADER_info);
290 } while (cas(&(s -> current_value), result, trec) != result);
294 static void unlock_tvar(StgTRecHeader *trec STG_UNUSED,
297 StgBool force_update STG_UNUSED) {
298 TRACE("%p : unlock_tvar(%p, %p)\n", trec, s, c);
299 ASSERT(s -> current_value == trec);
300 s -> current_value = c;
303 static StgBool cond_lock_tvar(StgTRecHeader *trec,
305 StgClosure *expected) {
307 TRACE("%p : cond_lock_tvar(%p, %p)\n", trec, s, expected);
308 result = cas(&(s -> current_value), expected, trec);
309 TRACE("%p : %s\n", trec, result ? "success" : "failure");
310 return (result == expected);
314 /*......................................................................*/
316 // Helper functions for thread blocking and unblocking
318 static void park_tso(StgTSO *tso) {
319 ASSERT(tso -> why_blocked == NotBlocked);
320 tso -> why_blocked = BlockedOnSTM;
321 tso -> block_info.closure = (StgClosure *) END_TSO_QUEUE;
322 TRACE("park_tso on tso=%p\n", tso);
325 static void unpark_tso(Capability *cap, StgTSO *tso) {
326 // We will continue unparking threads while they remain on one of the wait
327 // queues: it's up to the thread itself to remove it from the wait queues
328 // if it decides to do so when it is scheduled.
329 if (tso -> why_blocked == BlockedOnSTM) {
330 TRACE("unpark_tso on tso=%p\n", tso);
333 TRACE("spurious unpark_tso on tso=%p\n", tso);
337 static void unpark_waiters_on(Capability *cap, StgTVar *s) {
339 TRACE("unpark_waiters_on tvar=%p\n", s);
340 for (q = s -> first_wait_queue_entry;
341 q != END_STM_WAIT_QUEUE;
342 q = q -> next_queue_entry) {
343 unpark_tso(cap, q -> waiting_tso);
347 /*......................................................................*/
349 // Helper functions for allocation and initialization
351 static StgTVarWaitQueue *new_stg_tvar_wait_queue(Capability *cap,
352 StgTSO *waiting_tso) {
353 StgTVarWaitQueue *result;
354 result = (StgTVarWaitQueue *)allocateLocal(cap, sizeofW(StgTVarWaitQueue));
355 SET_HDR (result, &stg_TVAR_WAIT_QUEUE_info, CCS_SYSTEM);
356 result -> waiting_tso = waiting_tso;
360 static StgTRecChunk *new_stg_trec_chunk(Capability *cap) {
361 StgTRecChunk *result;
362 result = (StgTRecChunk *)allocateLocal(cap, sizeofW(StgTRecChunk));
363 SET_HDR (result, &stg_TREC_CHUNK_info, CCS_SYSTEM);
364 result -> prev_chunk = END_STM_CHUNK_LIST;
365 result -> next_entry_idx = 0;
369 static StgTRecHeader *new_stg_trec_header(Capability *cap,
370 StgTRecHeader *enclosing_trec) {
371 StgTRecHeader *result;
372 result = (StgTRecHeader *) allocateLocal(cap, sizeofW(StgTRecHeader));
373 SET_HDR (result, &stg_TREC_HEADER_info, CCS_SYSTEM);
375 result -> enclosing_trec = enclosing_trec;
376 result -> current_chunk = new_stg_trec_chunk(cap);
378 if (enclosing_trec == NO_TREC) {
379 result -> state = TREC_ACTIVE;
381 ASSERT(enclosing_trec -> state == TREC_ACTIVE ||
382 enclosing_trec -> state == TREC_CONDEMNED);
383 result -> state = enclosing_trec -> state;
389 static StgTVar *new_tvar(Capability *cap,
390 StgClosure *new_value) {
392 result = (StgTVar *)allocateLocal(cap, sizeofW(StgTVar));
393 SET_HDR (result, &stg_TVAR_info, CCS_SYSTEM);
394 result -> current_value = new_value;
395 result -> first_wait_queue_entry = END_STM_WAIT_QUEUE;
397 result -> last_update_by = NO_TREC;
402 /*......................................................................*/
404 // Helper functions for managing waiting lists
406 static void build_wait_queue_entries_for_trec(Capability *cap,
408 StgTRecHeader *trec) {
409 ASSERT(trec != NO_TREC);
410 ASSERT(trec -> enclosing_trec == NO_TREC);
411 ASSERT(trec -> state == TREC_ACTIVE);
413 TRACE("%p : build_wait_queue_entries_for_trec()\n", trec);
415 FOR_EACH_ENTRY(trec, e, {
418 StgTVarWaitQueue *fq;
420 TRACE("%p : adding tso=%p to wait queue for tvar=%p\n", trec, tso, s);
421 ACQ_ASSERT(s -> current_value == trec);
422 NACQ_ASSERT(s -> current_value == e -> expected_value);
423 fq = s -> first_wait_queue_entry;
424 q = new_stg_tvar_wait_queue(cap, tso);
425 q -> next_queue_entry = fq;
426 q -> prev_queue_entry = END_STM_WAIT_QUEUE;
427 if (fq != END_STM_WAIT_QUEUE) {
428 fq -> prev_queue_entry = q;
430 s -> first_wait_queue_entry = q;
431 e -> new_value = (StgClosure *) q;
435 static void remove_wait_queue_entries_for_trec(StgTRecHeader *trec) {
436 ASSERT(trec != NO_TREC);
437 ASSERT(trec -> enclosing_trec == NO_TREC);
438 ASSERT(trec -> state == TREC_WAITING ||
439 trec -> state == TREC_CONDEMNED);
441 TRACE("%p : remove_wait_queue_entries_for_trec()\n", trec);
443 FOR_EACH_ENTRY(trec, e, {
445 StgTVarWaitQueue *pq;
446 StgTVarWaitQueue *nq;
449 StgClosure *saw = lock_tvar(trec, s);
450 q = (StgTVarWaitQueue *) (e -> new_value);
451 TRACE("%p : removing tso=%p from wait queue for tvar=%p\n", trec, q -> waiting_tso, s);
452 ACQ_ASSERT(s -> current_value == trec);
453 nq = q -> next_queue_entry;
454 pq = q -> prev_queue_entry;
455 if (nq != END_STM_WAIT_QUEUE) {
456 nq -> prev_queue_entry = pq;
458 if (pq != END_STM_WAIT_QUEUE) {
459 pq -> next_queue_entry = nq;
461 ASSERT (s -> first_wait_queue_entry == q);
462 s -> first_wait_queue_entry = nq;
464 unlock_tvar(trec, s, saw, FALSE);
468 /*......................................................................*/
470 static TRecEntry *get_new_entry(Capability *cap,
476 c = t -> current_chunk;
477 i = c -> next_entry_idx;
478 ASSERT(c != END_STM_CHUNK_LIST);
480 if (i < TREC_CHUNK_NUM_ENTRIES) {
481 // Continue to use current chunk
482 result = &(c -> entries[i]);
483 c -> next_entry_idx ++;
485 // Current chunk is full: allocate a fresh one
487 nc = new_stg_trec_chunk(cap);
488 nc -> prev_chunk = c;
489 nc -> next_entry_idx = 1;
490 t -> current_chunk = nc;
491 result = &(nc -> entries[0]);
497 /*......................................................................*/
499 static void merge_update_into(Capability *cap,
502 StgClosure *expected_value,
503 StgClosure *new_value) {
506 // Look for an entry in this trec
508 FOR_EACH_ENTRY(t, e, {
513 if (e -> expected_value != expected_value) {
514 // Must abort if the two entries start from different values
515 TRACE("%p : entries inconsistent at %p (%p vs %p)\n",
516 t, tvar, e -> expected_value, expected_value);
517 t -> state = TREC_CONDEMNED;
519 e -> new_value = new_value;
525 // No entry so far in this trec
527 ne = get_new_entry(cap, t);
529 ne -> expected_value = expected_value;
530 ne -> new_value = new_value;
534 /*......................................................................*/
536 static StgBool entry_is_update(TRecEntry *e) {
538 result = (e -> expected_value != e -> new_value);
542 static StgBool entry_is_read_only(TRecEntry *e) {
544 result = (e -> expected_value == e -> new_value);
548 static StgBool tvar_is_locked(StgTVar *s, StgTRecHeader *h) {
551 c = s -> current_value;
552 result = (c == (StgClosure *) h);
556 // revert_ownership : release a lock on a TVar, storing back
557 // the value that it held when the lock was acquired. "revert_all"
558 // is set in stmWait and stmReWait when we acquired locks on all of
559 // the TVars involved. "revert_all" is not set in commit operations
560 // where we don't lock TVars that have been read from but not updated.
562 static void revert_ownership(StgTRecHeader *trec STG_UNUSED,
563 StgBool revert_all STG_UNUSED) {
564 #if defined(STM_FG_LOCKS)
565 FOR_EACH_ENTRY(trec, e, {
566 if (revert_all || entry_is_update(e)) {
569 if (tvar_is_locked(s, trec)) {
570 unlock_tvar(trec, s, e -> expected_value, TRUE);
577 /*......................................................................*/
579 // validate_and_acquire_ownership : this performs the twin functions
580 // of checking that the TVars referred to by entries in trec hold the
581 // expected values and:
583 // - locking the TVar (on updated TVars during commit, or all TVars
586 // - recording the identity of the TRec who wrote the value seen in the
587 // TVar (on non-updated TVars during commit). These values are
588 // stashed in the TRec entries and are then checked in check_read_only
589 // to ensure that an atomic snapshot of all of these locations has been
592 static StgBool validate_and_acquire_ownership (StgTRecHeader *trec,
594 int retain_ownership) {
598 TRACE("%p : shake, pretending trec is invalid when it may not be\n", trec);
602 ASSERT ((trec -> state == TREC_ACTIVE) ||
603 (trec -> state == TREC_WAITING) ||
604 (trec -> state == TREC_CONDEMNED));
605 result = !((trec -> state) == TREC_CONDEMNED);
607 FOR_EACH_ENTRY(trec, e, {
610 if (acquire_all || entry_is_update(e)) {
611 TRACE("%p : trying to acquire %p\n", trec, s);
612 if (!cond_lock_tvar(trec, s, e -> expected_value)) {
613 TRACE("%p : failed to acquire %p\n", trec, s);
618 ASSERT(use_read_phase);
620 TRACE("%p : will need to check %p\n", trec, s);
621 if (s -> current_value != e -> expected_value) {
622 TRACE("%p : doesn't match\n", trec);
626 e -> saw_update_by = s -> last_update_by;
627 if (s -> current_value != e -> expected_value) {
628 TRACE("%p : doesn't match (race)\n", trec);
632 TRACE("%p : need to check update by %p\n", trec, e -> saw_update_by);
639 if ((!result) || (!retain_ownership)) {
640 revert_ownership(trec, acquire_all);
646 // check_read_only : check that we've seen an atomic snapshot of the
647 // non-updated TVars accessed by a trec. This checks that the last TRec to
648 // commit an update to the TVar is unchanged since the value was stashed in
649 // validate_and_acquire_ownership. If no udpate is seen to any TVar than
650 // all of them contained their expected values at the start of the call to
653 // The paper "Concurrent programming without locks" (under submission), or
654 // Keir Fraser's PhD dissertation "Practical lock-free programming" discuss
655 // this kind of algorithm.
657 static StgBool check_read_only(StgTRecHeader *trec STG_UNUSED) {
658 StgBool result = TRUE;
660 ASSERT (use_read_phase);
662 FOR_EACH_ENTRY(trec, e, {
665 if (entry_is_read_only(e)) {
666 TRACE("%p : check_read_only for TVar %p, saw %p\n", trec, s, e -> saw_update_by);
667 if (s -> last_update_by != e -> saw_update_by) {
668 // ||s -> current_value != e -> expected_value) {
669 TRACE("%p : mismatch\n", trec);
681 /************************************************************************/
683 void stmPreGCHook() {
685 TRACE("stmPreGCHook\n");
689 /************************************************************************/
692 TRACE("initSTM, NO_TREC=%p\n", NO_TREC);
695 /*......................................................................*/
697 StgTRecHeader *stmStartTransaction(Capability *cap,
698 StgTRecHeader *outer) {
700 TRACE("%p : stmStartTransaction\n", outer);
701 t = new_stg_trec_header(cap, outer);
702 TRACE("%p : stmStartTransaction()=%p\n", outer, t);
706 /*......................................................................*/
708 void stmAbortTransaction(StgTRecHeader *trec) {
709 TRACE("%p : stmAbortTransaction\n", trec);
710 ASSERT (trec != NO_TREC);
711 ASSERT ((trec -> state == TREC_ACTIVE) ||
712 (trec -> state == TREC_WAITING) ||
713 (trec -> state == TREC_CONDEMNED));
716 if (trec -> state == TREC_WAITING) {
717 ASSERT (trec -> enclosing_trec == NO_TREC);
718 TRACE("%p : stmAbortTransaction aborting waiting transaction\n", trec);
719 remove_wait_queue_entries_for_trec(trec);
721 trec -> state = TREC_ABORTED;
724 TRACE("%p : stmAbortTransaction done\n", trec);
727 /*......................................................................*/
729 void stmCondemnTransaction(StgTRecHeader *trec) {
730 TRACE("%p : stmCondemnTransaction\n", trec);
731 ASSERT (trec != NO_TREC);
732 ASSERT ((trec -> state == TREC_ACTIVE) ||
733 (trec -> state == TREC_WAITING) ||
734 (trec -> state == TREC_CONDEMNED));
737 if (trec -> state == TREC_WAITING) {
738 ASSERT (trec -> enclosing_trec == NO_TREC);
739 TRACE("%p : stmCondemnTransaction condemning waiting transaction\n", trec);
740 remove_wait_queue_entries_for_trec(trec);
742 trec -> state = TREC_CONDEMNED;
745 TRACE("%p : stmCondemnTransaction done\n", trec);
748 /*......................................................................*/
750 StgTRecHeader *stmGetEnclosingTRec(StgTRecHeader *trec) {
751 StgTRecHeader *outer;
752 TRACE("%p : stmGetEnclosingTRec\n", trec);
753 outer = trec -> enclosing_trec;
754 TRACE("%p : stmGetEnclosingTRec()=%p\n", trec, outer);
758 /*......................................................................*/
760 StgBool stmValidateNestOfTransactions(StgTRecHeader *trec) {
764 TRACE("%p : stmValidateNestOfTransactions\n", trec);
765 ASSERT(trec != NO_TREC);
766 ASSERT((trec -> state == TREC_ACTIVE) ||
767 (trec -> state == TREC_WAITING) ||
768 (trec -> state == TREC_CONDEMNED));
774 while (t != NO_TREC) {
775 result &= validate_and_acquire_ownership(t, TRUE, FALSE);
776 t = t -> enclosing_trec;
779 if (!result && trec -> state != TREC_WAITING) {
780 trec -> state = TREC_CONDEMNED;
785 TRACE("%p : stmValidateNestOfTransactions()=%d\n", trec, result);
789 /*......................................................................*/
791 StgBool stmCommitTransaction(Capability *cap, StgTRecHeader *trec) {
794 TRACE("%p : stmCommitTransaction()\n", trec);
795 ASSERT (trec != NO_TREC);
796 ASSERT (trec -> enclosing_trec == NO_TREC);
797 ASSERT ((trec -> state == TREC_ACTIVE) ||
798 (trec -> state == TREC_CONDEMNED));
801 result = validate_and_acquire_ownership(trec, (!use_read_phase), TRUE);
803 // We now know that all the updated locations hold their expected values.
804 ASSERT (trec -> state == TREC_ACTIVE);
806 if (use_read_phase) {
807 TRACE("%p : doing read check\n", trec);
808 result = check_read_only(trec);
809 TRACE("%p : read-check %s\n", trec, result ? "succeeded" : "failed");
813 // We now know that all of the read-only locations held their exepcted values
814 // at the end of the call to validate_and_acquire_ownership. This forms the
815 // linearization point of the commit.
817 FOR_EACH_ENTRY(trec, e, {
820 if (e -> new_value != e -> expected_value) {
821 // Entry is an update: write the value back to the TVar, unlocking it if
824 ACQ_ASSERT(tvar_is_locked(s, trec));
825 TRACE("%p : writing %p to %p, waking waiters\n", trec, e -> new_value, s);
826 unpark_waiters_on(cap,s);
828 s -> last_update_by = trec;
830 unlock_tvar(trec, s, e -> new_value, TRUE);
832 ACQ_ASSERT(!tvar_is_locked(s, trec));
835 revert_ownership(trec, FALSE);
841 TRACE("%p : stmCommitTransaction()=%d\n", trec, result);
846 /*......................................................................*/
848 StgBool stmCommitNestedTransaction(Capability *cap, StgTRecHeader *trec) {
851 ASSERT (trec != NO_TREC && trec -> enclosing_trec != NO_TREC);
852 TRACE("%p : stmCommitNestedTransaction() into %p\n", trec, trec -> enclosing_trec);
853 ASSERT ((trec -> state == TREC_ACTIVE) || (trec -> state == TREC_CONDEMNED));
857 et = trec -> enclosing_trec;
858 result = validate_and_acquire_ownership(trec, FALSE, TRUE);
860 // We now know that all the updated locations hold their expected values.
862 if (use_read_phase) {
863 TRACE("%p : doing read check\n", trec);
864 result = check_read_only(trec);
867 // We now know that all of the read-only locations held their exepcted values
868 // at the end of the call to validate_and_acquire_ownership. This forms the
869 // linearization point of the commit.
872 TRACE("%p : read-check succeeded\n", trec);
873 FOR_EACH_ENTRY(trec, e, {
874 // Merge each entry into the enclosing transaction record, release all
879 if (entry_is_update(e)) {
880 unlock_tvar(trec, s, e -> expected_value, FALSE);
882 merge_update_into(cap, et, s, e -> expected_value, e -> new_value);
883 ACQ_ASSERT(s -> current_value != trec);
886 revert_ownership(trec, FALSE);
893 TRACE("%p : stmCommitNestedTransaction()=%d\n", trec, result);
898 /*......................................................................*/
900 StgBool stmWait(Capability *cap, StgTSO *tso, StgTRecHeader *trec) {
902 TRACE("%p : stmWait(%p)\n", trec, tso);
903 ASSERT (trec != NO_TREC);
904 ASSERT (trec -> enclosing_trec == NO_TREC);
905 ASSERT ((trec -> state == TREC_ACTIVE) ||
906 (trec -> state == TREC_CONDEMNED));
909 result = validate_and_acquire_ownership(trec, TRUE, TRUE);
911 // The transaction is valid so far so we can actually start waiting.
912 // (Otherwise the transaction was not valid and the thread will have to
915 // Put ourselves to sleep. We retain locks on all the TVars involved
916 // until we are sound asleep : (a) on the wait queues, (b) BlockedOnSTM
917 // in the TSO, (c) TREC_WAITING in the Trec.
918 build_wait_queue_entries_for_trec(cap, tso, trec);
920 trec -> state = TREC_WAITING;
922 // As soon as we start releasing ownership, another thread may find us
923 // and wake us up. This may happen even before we have finished
924 // releasing ownership.
925 revert_ownership(trec, TRUE);
930 TRACE("%p : stmWait(%p)=%d\n", trec, tso, result);
934 /*......................................................................*/
936 StgBool stmReWait(StgTSO *tso) {
938 StgTRecHeader *trec = tso->trec;
940 TRACE("%p : stmReWait\n", trec);
941 ASSERT (trec != NO_TREC);
942 ASSERT (trec -> enclosing_trec == NO_TREC);
943 ASSERT ((trec -> state == TREC_WAITING) ||
944 (trec -> state == TREC_CONDEMNED));
947 result = validate_and_acquire_ownership(trec, TRUE, TRUE);
948 TRACE("%p : validation %s\n", trec, result ? "succeeded" : "failed");
950 // The transaction remains valid -- do nothing because it is already on
952 ASSERT (trec -> state == TREC_WAITING);
954 revert_ownership(trec, TRUE);
956 // The transcation has become invalid. We can now remove it from the wait
958 if (trec -> state != TREC_CONDEMNED) {
959 remove_wait_queue_entries_for_trec (trec);
965 TRACE("%p : stmReWait()=%d\n", trec, result);
969 /*......................................................................*/
971 static TRecEntry *get_entry_for(StgTRecHeader *trec, StgTVar *tvar, StgTRecHeader **in) {
972 TRecEntry *result = NULL;
974 TRACE("%p : get_entry_for TVar %p\n", trec, tvar);
975 ASSERT(trec != NO_TREC);
978 FOR_EACH_ENTRY(trec, e, {
979 if (e -> tvar == tvar) {
987 trec = trec -> enclosing_trec;
988 } while (result == NULL && trec != NO_TREC);
993 static StgClosure *read_current_value(StgTRecHeader *trec STG_UNUSED, StgTVar *tvar) {
995 result = tvar -> current_value;
997 #if defined(STM_FG_LOCKS)
998 while (GET_INFO(result) == &stg_TREC_HEADER_info) {
999 TRACE("%p : read_current_value(%p) saw %p\n", trec, tvar, result);
1000 result = tvar -> current_value;
1004 TRACE("%p : read_current_value(%p)=%p\n", trec, tvar, result);
1008 /*......................................................................*/
1010 StgClosure *stmReadTVar(Capability *cap,
1011 StgTRecHeader *trec,
1013 StgTRecHeader *entry_in;
1014 StgClosure *result = NULL;
1015 TRecEntry *entry = NULL;
1016 TRACE("%p : stmReadTVar(%p)\n", trec, tvar);
1017 ASSERT (trec != NO_TREC);
1018 ASSERT (trec -> state == TREC_ACTIVE ||
1019 trec -> state == TREC_CONDEMNED);
1021 entry = get_entry_for(trec, tvar, &entry_in);
1023 if (entry != NULL) {
1024 if (entry_in == trec) {
1025 // Entry found in our trec
1026 result = entry -> new_value;
1028 // Entry found in another trec
1029 TRecEntry *new_entry = get_new_entry(cap, trec);
1030 new_entry -> tvar = tvar;
1031 new_entry -> expected_value = entry -> expected_value;
1032 new_entry -> new_value = entry -> new_value;
1033 result = new_entry -> new_value;
1037 StgClosure *current_value = read_current_value(trec, tvar);
1038 TRecEntry *new_entry = get_new_entry(cap, trec);
1039 new_entry -> tvar = tvar;
1040 new_entry -> expected_value = current_value;
1041 new_entry -> new_value = current_value;
1042 result = current_value;
1045 TRACE("%p : stmReadTVar(%p)=%p\n", trec, tvar, result);
1049 /*......................................................................*/
1051 void stmWriteTVar(Capability *cap,
1052 StgTRecHeader *trec,
1054 StgClosure *new_value) {
1056 StgTRecHeader *entry_in;
1057 TRecEntry *entry = NULL;
1058 TRACE("%p : stmWriteTVar(%p, %p)\n", trec, tvar, new_value);
1059 ASSERT (trec != NO_TREC);
1060 ASSERT (trec -> state == TREC_ACTIVE ||
1061 trec -> state == TREC_CONDEMNED);
1063 entry = get_entry_for(trec, tvar, &entry_in);
1065 if (entry != NULL) {
1066 if (entry_in == trec) {
1067 // Entry found in our trec
1068 entry -> new_value = new_value;
1070 // Entry found in another trec
1071 TRecEntry *new_entry = get_new_entry(cap, trec);
1072 new_entry -> tvar = tvar;
1073 new_entry -> expected_value = entry -> expected_value;
1074 new_entry -> new_value = new_value;
1078 StgClosure *current_value = read_current_value(trec, tvar);
1079 TRecEntry *new_entry = get_new_entry(cap, trec);
1080 new_entry -> tvar = tvar;
1081 new_entry -> expected_value = current_value;
1082 new_entry -> new_value = new_value;
1085 TRACE("%p : stmWriteTVar done\n", trec);
1088 /*......................................................................*/
1090 StgTVar *stmNewTVar(Capability *cap,
1091 StgClosure *new_value) {
1093 result = new_tvar(cap, new_value);
1097 /*......................................................................*/