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);
331 tso -> why_blocked = NotBlocked;
332 pushOnRunQueue(cap,tso);
334 TRACE("spurious unpark_tso on tso=%p\n", tso);
338 static void unpark_waiters_on(Capability *cap, StgTVar *s) {
340 TRACE("unpark_waiters_on tvar=%p\n", s);
341 for (q = s -> first_wait_queue_entry;
342 q != END_STM_WAIT_QUEUE;
343 q = q -> next_queue_entry) {
344 unpark_tso(cap, q -> waiting_tso);
348 /*......................................................................*/
350 // Helper functions for allocation and initialization
352 static StgTVarWaitQueue *new_stg_tvar_wait_queue(Capability *cap,
353 StgTSO *waiting_tso) {
354 StgTVarWaitQueue *result;
355 result = (StgTVarWaitQueue *)allocateLocal(cap, sizeofW(StgTVarWaitQueue));
356 SET_HDR (result, &stg_TVAR_WAIT_QUEUE_info, CCS_SYSTEM);
357 result -> waiting_tso = waiting_tso;
361 static StgTRecChunk *new_stg_trec_chunk(Capability *cap) {
362 StgTRecChunk *result;
363 result = (StgTRecChunk *)allocateLocal(cap, sizeofW(StgTRecChunk));
364 SET_HDR (result, &stg_TREC_CHUNK_info, CCS_SYSTEM);
365 result -> prev_chunk = END_STM_CHUNK_LIST;
366 result -> next_entry_idx = 0;
370 static StgTRecHeader *new_stg_trec_header(Capability *cap,
371 StgTRecHeader *enclosing_trec) {
372 StgTRecHeader *result;
373 result = (StgTRecHeader *) allocateLocal(cap, sizeofW(StgTRecHeader));
374 SET_HDR (result, &stg_TREC_HEADER_info, CCS_SYSTEM);
376 result -> enclosing_trec = enclosing_trec;
377 result -> current_chunk = new_stg_trec_chunk(cap);
379 if (enclosing_trec == NO_TREC) {
380 result -> state = TREC_ACTIVE;
382 ASSERT(enclosing_trec -> state == TREC_ACTIVE ||
383 enclosing_trec -> state == TREC_CONDEMNED);
384 result -> state = enclosing_trec -> state;
390 static StgTVar *new_tvar(Capability *cap,
391 StgClosure *new_value) {
393 result = (StgTVar *)allocateLocal(cap, sizeofW(StgTVar));
394 SET_HDR (result, &stg_TVAR_info, CCS_SYSTEM);
395 result -> current_value = new_value;
396 result -> first_wait_queue_entry = END_STM_WAIT_QUEUE;
398 result -> last_update_by = NO_TREC;
403 /*......................................................................*/
405 // Helper functions for managing waiting lists
407 static void build_wait_queue_entries_for_trec(Capability *cap,
409 StgTRecHeader *trec) {
410 ASSERT(trec != NO_TREC);
411 ASSERT(trec -> enclosing_trec == NO_TREC);
412 ASSERT(trec -> state == TREC_ACTIVE);
414 TRACE("%p : build_wait_queue_entries_for_trec()\n", trec);
416 FOR_EACH_ENTRY(trec, e, {
419 StgTVarWaitQueue *fq;
421 TRACE("%p : adding tso=%p to wait queue for tvar=%p\n", trec, tso, s);
422 ACQ_ASSERT(s -> current_value == trec);
423 NACQ_ASSERT(s -> current_value == e -> expected_value);
424 fq = s -> first_wait_queue_entry;
425 q = new_stg_tvar_wait_queue(cap, tso);
426 q -> next_queue_entry = fq;
427 q -> prev_queue_entry = END_STM_WAIT_QUEUE;
428 if (fq != END_STM_WAIT_QUEUE) {
429 fq -> prev_queue_entry = q;
431 s -> first_wait_queue_entry = q;
432 e -> new_value = (StgClosure *) q;
436 static void remove_wait_queue_entries_for_trec(StgTRecHeader *trec) {
437 ASSERT(trec != NO_TREC);
438 ASSERT(trec -> enclosing_trec == NO_TREC);
439 ASSERT(trec -> state == TREC_WAITING ||
440 trec -> state == TREC_CONDEMNED);
442 TRACE("%p : remove_wait_queue_entries_for_trec()\n", trec);
444 FOR_EACH_ENTRY(trec, e, {
446 StgTVarWaitQueue *pq;
447 StgTVarWaitQueue *nq;
450 StgClosure *saw = lock_tvar(trec, s);
451 q = (StgTVarWaitQueue *) (e -> new_value);
452 TRACE("%p : removing tso=%p from wait queue for tvar=%p\n", trec, q -> waiting_tso, s);
453 ACQ_ASSERT(s -> current_value == trec);
454 nq = q -> next_queue_entry;
455 pq = q -> prev_queue_entry;
456 if (nq != END_STM_WAIT_QUEUE) {
457 nq -> prev_queue_entry = pq;
459 if (pq != END_STM_WAIT_QUEUE) {
460 pq -> next_queue_entry = nq;
462 ASSERT (s -> first_wait_queue_entry == q);
463 s -> first_wait_queue_entry = nq;
465 unlock_tvar(trec, s, saw, FALSE);
469 /*......................................................................*/
471 static TRecEntry *get_new_entry(Capability *cap,
477 c = t -> current_chunk;
478 i = c -> next_entry_idx;
479 ASSERT(c != END_STM_CHUNK_LIST);
481 if (i < TREC_CHUNK_NUM_ENTRIES) {
482 // Continue to use current chunk
483 result = &(c -> entries[i]);
484 c -> next_entry_idx ++;
486 // Current chunk is full: allocate a fresh one
488 nc = new_stg_trec_chunk(cap);
489 nc -> prev_chunk = c;
490 nc -> next_entry_idx = 1;
491 t -> current_chunk = nc;
492 result = &(nc -> entries[0]);
498 /*......................................................................*/
500 static void merge_update_into(Capability *cap,
503 StgClosure *expected_value,
504 StgClosure *new_value) {
507 // Look for an entry in this trec
509 FOR_EACH_ENTRY(t, e, {
514 if (e -> expected_value != expected_value) {
515 // Must abort if the two entries start from different values
516 TRACE("%p : entries inconsistent at %p (%p vs %p)\n",
517 t, tvar, e -> expected_value, expected_value);
518 t -> state = TREC_CONDEMNED;
520 e -> new_value = new_value;
526 // No entry so far in this trec
528 ne = get_new_entry(cap, t);
530 ne -> expected_value = expected_value;
531 ne -> new_value = new_value;
535 /*......................................................................*/
537 static StgBool entry_is_update(TRecEntry *e) {
539 result = (e -> expected_value != e -> new_value);
543 static StgBool entry_is_read_only(TRecEntry *e) {
545 result = (e -> expected_value == e -> new_value);
549 static StgBool tvar_is_locked(StgTVar *s, StgTRecHeader *h) {
552 c = s -> current_value;
553 result = (c == (StgClosure *) h);
557 // revert_ownership : release a lock on a TVar, storing back
558 // the value that it held when the lock was acquired. "revert_all"
559 // is set in stmWait and stmReWait when we acquired locks on all of
560 // the TVars involved. "revert_all" is not set in commit operations
561 // where we don't lock TVars that have been read from but not updated.
563 static void revert_ownership(StgTRecHeader *trec STG_UNUSED,
564 StgBool revert_all STG_UNUSED) {
565 #if defined(STM_FG_LOCKS)
566 FOR_EACH_ENTRY(trec, e, {
567 if (revert_all || entry_is_update(e)) {
570 if (tvar_is_locked(s, trec)) {
571 unlock_tvar(trec, s, e -> expected_value, TRUE);
578 /*......................................................................*/
580 // validate_and_acquire_ownership : this performs the twin functions
581 // of checking that the TVars referred to by entries in trec hold the
582 // expected values and:
584 // - locking the TVar (on updated TVars during commit, or all TVars
587 // - recording the identity of the TRec who wrote the value seen in the
588 // TVar (on non-updated TVars during commit). These values are
589 // stashed in the TRec entries and are then checked in check_read_only
590 // to ensure that an atomic snapshot of all of these locations has been
593 static StgBool validate_and_acquire_ownership (StgTRecHeader *trec,
595 int retain_ownership) {
599 TRACE("%p : shake, pretending trec is invalid when it may not be\n", trec);
603 ASSERT ((trec -> state == TREC_ACTIVE) ||
604 (trec -> state == TREC_WAITING) ||
605 (trec -> state == TREC_CONDEMNED));
606 result = !((trec -> state) == TREC_CONDEMNED);
608 FOR_EACH_ENTRY(trec, e, {
611 if (acquire_all || entry_is_update(e)) {
612 TRACE("%p : trying to acquire %p\n", trec, s);
613 if (!cond_lock_tvar(trec, s, e -> expected_value)) {
614 TRACE("%p : failed to acquire %p\n", trec, s);
619 ASSERT(use_read_phase);
621 TRACE("%p : will need to check %p\n", trec, s);
622 if (s -> current_value != e -> expected_value) {
623 TRACE("%p : doesn't match\n", trec);
627 e -> saw_update_by = s -> last_update_by;
628 if (s -> current_value != e -> expected_value) {
629 TRACE("%p : doesn't match (race)\n", trec);
633 TRACE("%p : need to check update by %p\n", trec, e -> saw_update_by);
640 if ((!result) || (!retain_ownership)) {
641 revert_ownership(trec, acquire_all);
647 // check_read_only : check that we've seen an atomic snapshot of the
648 // non-updated TVars accessed by a trec. This checks that the last TRec to
649 // commit an update to the TVar is unchanged since the value was stashed in
650 // validate_and_acquire_ownership. If no udpate is seen to any TVar than
651 // all of them contained their expected values at the start of the call to
654 // The paper "Concurrent programming without locks" (under submission), or
655 // Keir Fraser's PhD dissertation "Practical lock-free programming" discuss
656 // this kind of algorithm.
658 static StgBool check_read_only(StgTRecHeader *trec STG_UNUSED) {
659 StgBool result = TRUE;
661 ASSERT (use_read_phase);
663 FOR_EACH_ENTRY(trec, e, {
666 if (entry_is_read_only(e)) {
667 TRACE("%p : check_read_only for TVar %p, saw %p\n", trec, s, e -> saw_update_by);
668 if (s -> last_update_by != e -> saw_update_by) {
669 // ||s -> current_value != e -> expected_value) {
670 TRACE("%p : mismatch\n", trec);
682 /************************************************************************/
684 void stmPreGCHook() {
686 TRACE("stmPreGCHook\n");
690 /************************************************************************/
693 TRACE("initSTM, NO_TREC=%p\n", NO_TREC);
696 /*......................................................................*/
698 StgTRecHeader *stmStartTransaction(Capability *cap,
699 StgTRecHeader *outer) {
701 TRACE("%p : stmStartTransaction\n", outer);
702 t = new_stg_trec_header(cap, outer);
703 TRACE("%p : stmStartTransaction()=%p\n", outer, t);
707 /*......................................................................*/
709 void stmAbortTransaction(StgTRecHeader *trec) {
710 TRACE("%p : stmAbortTransaction\n", trec);
711 ASSERT (trec != NO_TREC);
712 ASSERT ((trec -> state == TREC_ACTIVE) ||
713 (trec -> state == TREC_WAITING) ||
714 (trec -> state == TREC_CONDEMNED));
717 if (trec -> state == TREC_WAITING) {
718 ASSERT (trec -> enclosing_trec == NO_TREC);
719 TRACE("%p : stmAbortTransaction aborting waiting transaction\n", trec);
720 remove_wait_queue_entries_for_trec(trec);
722 trec -> state = TREC_ABORTED;
725 TRACE("%p : stmAbortTransaction done\n", trec);
728 /*......................................................................*/
730 void stmCondemnTransaction(StgTRecHeader *trec) {
731 TRACE("%p : stmCondemnTransaction\n", trec);
732 ASSERT (trec != NO_TREC);
733 ASSERT ((trec -> state == TREC_ACTIVE) ||
734 (trec -> state == TREC_WAITING) ||
735 (trec -> state == TREC_CONDEMNED));
738 if (trec -> state == TREC_WAITING) {
739 ASSERT (trec -> enclosing_trec == NO_TREC);
740 TRACE("%p : stmCondemnTransaction condemning waiting transaction\n", trec);
741 remove_wait_queue_entries_for_trec(trec);
743 trec -> state = TREC_CONDEMNED;
746 TRACE("%p : stmCondemnTransaction done\n", trec);
749 /*......................................................................*/
751 StgTRecHeader *stmGetEnclosingTRec(StgTRecHeader *trec) {
752 StgTRecHeader *outer;
753 TRACE("%p : stmGetEnclosingTRec\n", trec);
754 outer = trec -> enclosing_trec;
755 TRACE("%p : stmGetEnclosingTRec()=%p\n", trec, outer);
759 /*......................................................................*/
761 StgBool stmValidateNestOfTransactions(StgTRecHeader *trec) {
765 TRACE("%p : stmValidateNestOfTransactions\n", trec);
766 ASSERT(trec != NO_TREC);
767 ASSERT((trec -> state == TREC_ACTIVE) ||
768 (trec -> state == TREC_WAITING) ||
769 (trec -> state == TREC_CONDEMNED));
775 while (t != NO_TREC) {
776 result &= validate_and_acquire_ownership(t, TRUE, FALSE);
777 t = t -> enclosing_trec;
780 if (!result && trec -> state != TREC_WAITING) {
781 trec -> state = TREC_CONDEMNED;
786 TRACE("%p : stmValidateNestOfTransactions()=%d\n", trec, result);
790 /*......................................................................*/
792 StgBool stmCommitTransaction(Capability *cap, StgTRecHeader *trec) {
795 TRACE("%p : stmCommitTransaction()\n", trec);
796 ASSERT (trec != NO_TREC);
797 ASSERT (trec -> enclosing_trec == NO_TREC);
798 ASSERT ((trec -> state == TREC_ACTIVE) ||
799 (trec -> state == TREC_CONDEMNED));
802 result = validate_and_acquire_ownership(trec, (!use_read_phase), TRUE);
804 // We now know that all the updated locations hold their expected values.
805 ASSERT (trec -> state == TREC_ACTIVE);
807 if (use_read_phase) {
808 TRACE("%p : doing read check\n", trec);
809 result = check_read_only(trec);
810 TRACE("%p : read-check %s\n", trec, result ? "succeeded" : "failed");
814 // We now know that all of the read-only locations held their exepcted values
815 // at the end of the call to validate_and_acquire_ownership. This forms the
816 // linearization point of the commit.
818 FOR_EACH_ENTRY(trec, e, {
821 if (e -> new_value != e -> expected_value) {
822 // Entry is an update: write the value back to the TVar, unlocking it if
825 ACQ_ASSERT(tvar_is_locked(s, trec));
826 TRACE("%p : writing %p to %p, waking waiters\n", trec, e -> new_value, s);
827 unpark_waiters_on(cap,s);
829 s -> last_update_by = trec;
831 unlock_tvar(trec, s, e -> new_value, TRUE);
833 ACQ_ASSERT(!tvar_is_locked(s, trec));
836 revert_ownership(trec, FALSE);
842 TRACE("%p : stmCommitTransaction()=%d\n", trec, result);
847 /*......................................................................*/
849 StgBool stmCommitNestedTransaction(Capability *cap, StgTRecHeader *trec) {
852 ASSERT (trec != NO_TREC && trec -> enclosing_trec != NO_TREC);
853 TRACE("%p : stmCommitNestedTransaction() into %p\n", trec, trec -> enclosing_trec);
854 ASSERT ((trec -> state == TREC_ACTIVE) || (trec -> state == TREC_CONDEMNED));
858 et = trec -> enclosing_trec;
859 result = validate_and_acquire_ownership(trec, FALSE, TRUE);
861 // We now know that all the updated locations hold their expected values.
863 if (use_read_phase) {
864 TRACE("%p : doing read check\n", trec);
865 result = check_read_only(trec);
868 // We now know that all of the read-only locations held their exepcted values
869 // at the end of the call to validate_and_acquire_ownership. This forms the
870 // linearization point of the commit.
873 TRACE("%p : read-check succeeded\n", trec);
874 FOR_EACH_ENTRY(trec, e, {
875 // Merge each entry into the enclosing transaction record, release all
880 if (entry_is_update(e)) {
881 unlock_tvar(trec, s, e -> expected_value, FALSE);
883 merge_update_into(cap, et, s, e -> expected_value, e -> new_value);
884 ACQ_ASSERT(s -> current_value != trec);
887 revert_ownership(trec, FALSE);
894 TRACE("%p : stmCommitNestedTransaction()=%d\n", trec, result);
899 /*......................................................................*/
901 StgBool stmWait(Capability *cap, StgTSO *tso, StgTRecHeader *trec) {
903 TRACE("%p : stmWait(%p)\n", trec, tso);
904 ASSERT (trec != NO_TREC);
905 ASSERT (trec -> enclosing_trec == NO_TREC);
906 ASSERT ((trec -> state == TREC_ACTIVE) ||
907 (trec -> state == TREC_CONDEMNED));
910 result = validate_and_acquire_ownership(trec, TRUE, TRUE);
912 // The transaction is valid so far so we can actually start waiting.
913 // (Otherwise the transaction was not valid and the thread will have to
916 // Put ourselves to sleep. We retain locks on all the TVars involved
917 // until we are sound asleep : (a) on the wait queues, (b) BlockedOnSTM
918 // in the TSO, (c) TREC_WAITING in the Trec.
919 build_wait_queue_entries_for_trec(cap, tso, trec);
921 trec -> state = TREC_WAITING;
923 // As soon as we start releasing ownership, another thread may find us
924 // and wake us up. This may happen even before we have finished
925 // releasing ownership.
926 revert_ownership(trec, TRUE);
931 TRACE("%p : stmWait(%p)=%d\n", trec, tso, result);
935 /*......................................................................*/
937 StgBool stmReWait(StgTSO *tso) {
939 StgTRecHeader *trec = tso->trec;
941 TRACE("%p : stmReWait\n", trec);
942 ASSERT (trec != NO_TREC);
943 ASSERT (trec -> enclosing_trec == NO_TREC);
944 ASSERT ((trec -> state == TREC_WAITING) ||
945 (trec -> state == TREC_CONDEMNED));
948 result = validate_and_acquire_ownership(trec, TRUE, TRUE);
949 TRACE("%p : validation %s\n", trec, result ? "succeeded" : "failed");
951 // The transaction remains valid -- do nothing because it is already on
953 ASSERT (trec -> state == TREC_WAITING);
955 revert_ownership(trec, TRUE);
957 // The transcation has become invalid. We can now remove it from the wait
959 if (trec -> state != TREC_CONDEMNED) {
960 remove_wait_queue_entries_for_trec (trec);
966 TRACE("%p : stmReWait()=%d\n", trec, result);
970 /*......................................................................*/
972 static TRecEntry *get_entry_for(StgTRecHeader *trec, StgTVar *tvar, StgTRecHeader **in) {
973 TRecEntry *result = NULL;
975 TRACE("%p : get_entry_for TVar %p\n", trec, tvar);
976 ASSERT(trec != NO_TREC);
979 FOR_EACH_ENTRY(trec, e, {
980 if (e -> tvar == tvar) {
988 trec = trec -> enclosing_trec;
989 } while (result == NULL && trec != NO_TREC);
994 static StgClosure *read_current_value(StgTRecHeader *trec STG_UNUSED, StgTVar *tvar) {
996 result = tvar -> current_value;
998 #if defined(STM_FG_LOCKS)
999 while (GET_INFO(result) == &stg_TREC_HEADER_info) {
1000 TRACE("%p : read_current_value(%p) saw %p\n", trec, tvar, result);
1001 result = tvar -> current_value;
1005 TRACE("%p : read_current_value(%p)=%p\n", trec, tvar, result);
1009 /*......................................................................*/
1011 StgClosure *stmReadTVar(Capability *cap,
1012 StgTRecHeader *trec,
1014 StgTRecHeader *entry_in;
1015 StgClosure *result = NULL;
1016 TRecEntry *entry = NULL;
1017 TRACE("%p : stmReadTVar(%p)\n", trec, tvar);
1018 ASSERT (trec != NO_TREC);
1019 ASSERT (trec -> state == TREC_ACTIVE ||
1020 trec -> state == TREC_CONDEMNED);
1022 entry = get_entry_for(trec, tvar, &entry_in);
1024 if (entry != NULL) {
1025 if (entry_in == trec) {
1026 // Entry found in our trec
1027 result = entry -> new_value;
1029 // Entry found in another trec
1030 TRecEntry *new_entry = get_new_entry(cap, trec);
1031 new_entry -> tvar = tvar;
1032 new_entry -> expected_value = entry -> expected_value;
1033 new_entry -> new_value = entry -> new_value;
1034 result = new_entry -> new_value;
1038 StgClosure *current_value = read_current_value(trec, tvar);
1039 TRecEntry *new_entry = get_new_entry(cap, trec);
1040 new_entry -> tvar = tvar;
1041 new_entry -> expected_value = current_value;
1042 new_entry -> new_value = current_value;
1043 result = current_value;
1046 TRACE("%p : stmReadTVar(%p)=%p\n", trec, tvar, result);
1050 /*......................................................................*/
1052 void stmWriteTVar(Capability *cap,
1053 StgTRecHeader *trec,
1055 StgClosure *new_value) {
1057 StgTRecHeader *entry_in;
1058 TRecEntry *entry = NULL;
1059 TRACE("%p : stmWriteTVar(%p, %p)\n", trec, tvar, new_value);
1060 ASSERT (trec != NO_TREC);
1061 ASSERT (trec -> state == TREC_ACTIVE ||
1062 trec -> state == TREC_CONDEMNED);
1064 entry = get_entry_for(trec, tvar, &entry_in);
1066 if (entry != NULL) {
1067 if (entry_in == trec) {
1068 // Entry found in our trec
1069 entry -> new_value = new_value;
1071 // Entry found in another trec
1072 TRecEntry *new_entry = get_new_entry(cap, trec);
1073 new_entry -> tvar = tvar;
1074 new_entry -> expected_value = entry -> expected_value;
1075 new_entry -> new_value = new_value;
1079 StgClosure *current_value = read_current_value(trec, tvar);
1080 TRecEntry *new_entry = get_new_entry(cap, trec);
1081 new_entry -> tvar = tvar;
1082 new_entry -> expected_value = current_value;
1083 new_entry -> new_value = new_value;
1086 TRACE("%p : stmWriteTVar done\n", trec);
1089 /*......................................................................*/
1091 StgTVar *stmNewTVar(Capability *cap,
1092 StgClosure *new_value) {
1094 result = new_tvar(cap, new_value);
1098 /*......................................................................*/