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 ACQUIRE_LOCK(&sched_mutex);
320 ASSERT(tso -> why_blocked == NotBlocked);
321 tso -> why_blocked = BlockedOnSTM;
322 tso -> block_info.closure = (StgClosure *) END_TSO_QUEUE;
323 RELEASE_LOCK(&sched_mutex);
324 TRACE("park_tso on tso=%p\n", tso);
327 static void unpark_tso(StgTSO *tso) {
328 // We will continue unparking threads while they remain on one of the wait
329 // queues: it's up to the thread itself to remove it from the wait queues
330 // if it decides to do so when it is scheduled.
331 if (tso -> why_blocked == BlockedOnSTM) {
332 TRACE("unpark_tso on tso=%p\n", tso);
333 ACQUIRE_LOCK(&sched_mutex);
334 tso -> why_blocked = NotBlocked;
335 PUSH_ON_RUN_QUEUE(tso);
336 RELEASE_LOCK(&sched_mutex);
338 TRACE("spurious unpark_tso on tso=%p\n", tso);
342 static void unpark_waiters_on(StgTVar *s) {
344 TRACE("unpark_waiters_on tvar=%p\n", s);
345 for (q = s -> first_wait_queue_entry;
346 q != END_STM_WAIT_QUEUE;
347 q = q -> next_queue_entry) {
348 unpark_tso(q -> waiting_tso);
352 /*......................................................................*/
354 // Helper functions for allocation and initialization
356 static StgTVarWaitQueue *new_stg_tvar_wait_queue(StgRegTable *reg,
357 StgTSO *waiting_tso) {
358 StgTVarWaitQueue *result;
359 result = (StgTVarWaitQueue *)allocateLocal(reg, sizeofW(StgTVarWaitQueue));
360 SET_HDR (result, &stg_TVAR_WAIT_QUEUE_info, CCS_SYSTEM);
361 result -> waiting_tso = waiting_tso;
365 static StgTRecChunk *new_stg_trec_chunk(StgRegTable *reg) {
366 StgTRecChunk *result;
367 result = (StgTRecChunk *)allocateLocal(reg, sizeofW(StgTRecChunk));
368 SET_HDR (result, &stg_TREC_CHUNK_info, CCS_SYSTEM);
369 result -> prev_chunk = END_STM_CHUNK_LIST;
370 result -> next_entry_idx = 0;
374 static StgTRecHeader *new_stg_trec_header(StgRegTable *reg,
375 StgTRecHeader *enclosing_trec) {
376 StgTRecHeader *result;
377 result = (StgTRecHeader *) allocateLocal(reg, sizeofW(StgTRecHeader));
378 SET_HDR (result, &stg_TREC_HEADER_info, CCS_SYSTEM);
380 result -> enclosing_trec = enclosing_trec;
381 result -> current_chunk = new_stg_trec_chunk(reg);
383 if (enclosing_trec == NO_TREC) {
384 result -> state = TREC_ACTIVE;
386 ASSERT(enclosing_trec -> state == TREC_ACTIVE ||
387 enclosing_trec -> state == TREC_CONDEMNED);
388 result -> state = enclosing_trec -> state;
394 static StgTVar *new_tvar(StgRegTable *reg,
395 StgClosure *new_value) {
397 result = (StgTVar *)allocateLocal(reg, sizeofW(StgTVar));
398 SET_HDR (result, &stg_TVAR_info, CCS_SYSTEM);
399 result -> current_value = new_value;
400 result -> first_wait_queue_entry = END_STM_WAIT_QUEUE;
402 result -> last_update_by = NO_TREC;
407 /*......................................................................*/
409 // Helper functions for managing waiting lists
411 static void build_wait_queue_entries_for_trec(StgRegTable *reg,
413 StgTRecHeader *trec) {
414 ASSERT(trec != NO_TREC);
415 ASSERT(trec -> enclosing_trec == NO_TREC);
416 ASSERT(trec -> state == TREC_ACTIVE);
418 TRACE("%p : build_wait_queue_entries_for_trec()\n", trec);
420 FOR_EACH_ENTRY(trec, e, {
423 StgTVarWaitQueue *fq;
425 TRACE("%p : adding tso=%p to wait queue for tvar=%p\n", trec, tso, s);
426 ACQ_ASSERT(s -> current_value == trec);
427 NACQ_ASSERT(s -> current_value == e -> expected_value);
428 fq = s -> first_wait_queue_entry;
429 q = new_stg_tvar_wait_queue(reg, tso);
430 q -> next_queue_entry = fq;
431 q -> prev_queue_entry = END_STM_WAIT_QUEUE;
432 if (fq != END_STM_WAIT_QUEUE) {
433 fq -> prev_queue_entry = q;
435 s -> first_wait_queue_entry = q;
436 e -> new_value = (StgClosure *) q;
440 static void remove_wait_queue_entries_for_trec(StgTRecHeader *trec) {
441 ASSERT(trec != NO_TREC);
442 ASSERT(trec -> enclosing_trec == NO_TREC);
443 ASSERT(trec -> state == TREC_WAITING ||
444 trec -> state == TREC_CONDEMNED);
446 TRACE("%p : remove_wait_queue_entries_for_trec()\n", trec);
448 FOR_EACH_ENTRY(trec, e, {
450 StgTVarWaitQueue *pq;
451 StgTVarWaitQueue *nq;
454 StgClosure *saw = lock_tvar(trec, s);
455 q = (StgTVarWaitQueue *) (e -> new_value);
456 TRACE("%p : removing tso=%p from wait queue for tvar=%p\n", trec, q -> waiting_tso, s);
457 ACQ_ASSERT(s -> current_value == trec);
458 nq = q -> next_queue_entry;
459 pq = q -> prev_queue_entry;
460 if (nq != END_STM_WAIT_QUEUE) {
461 nq -> prev_queue_entry = pq;
463 if (pq != END_STM_WAIT_QUEUE) {
464 pq -> next_queue_entry = nq;
466 ASSERT (s -> first_wait_queue_entry == q);
467 s -> first_wait_queue_entry = nq;
469 unlock_tvar(trec, s, saw, FALSE);
473 /*......................................................................*/
475 static TRecEntry *get_new_entry(StgRegTable *reg,
481 c = t -> current_chunk;
482 i = c -> next_entry_idx;
483 ASSERT(c != END_STM_CHUNK_LIST);
485 if (i < TREC_CHUNK_NUM_ENTRIES) {
486 // Continue to use current chunk
487 result = &(c -> entries[i]);
488 c -> next_entry_idx ++;
490 // Current chunk is full: allocate a fresh one
492 nc = new_stg_trec_chunk(reg);
493 nc -> prev_chunk = c;
494 nc -> next_entry_idx = 1;
495 t -> current_chunk = nc;
496 result = &(nc -> entries[0]);
502 /*......................................................................*/
504 static void merge_update_into(StgRegTable *reg,
507 StgClosure *expected_value,
508 StgClosure *new_value) {
511 // Look for an entry in this trec
513 FOR_EACH_ENTRY(t, e, {
518 if (e -> expected_value != expected_value) {
519 // Must abort if the two entries start from different values
520 TRACE("%p : entries inconsistent at %p (%p vs %p)\n",
521 t, tvar, e -> expected_value, expected_value);
522 t -> state = TREC_CONDEMNED;
524 e -> new_value = new_value;
530 // No entry so far in this trec
532 ne = get_new_entry(reg, t);
534 ne -> expected_value = expected_value;
535 ne -> new_value = new_value;
539 /*......................................................................*/
541 static StgBool entry_is_update(TRecEntry *e) {
543 result = (e -> expected_value != e -> new_value);
547 static StgBool entry_is_read_only(TRecEntry *e) {
549 result = (e -> expected_value == e -> new_value);
553 static StgBool tvar_is_locked(StgTVar *s, StgTRecHeader *h) {
556 c = s -> current_value;
557 result = (c == (StgClosure *) h);
561 // revert_ownership : release a lock on a TVar, storing back
562 // the value that it held when the lock was acquired. "revert_all"
563 // is set in stmWait and stmReWait when we acquired locks on all of
564 // the TVars involved. "revert_all" is not set in commit operations
565 // where we don't lock TVars that have been read from but not updated.
567 static void revert_ownership(StgTRecHeader *trec STG_UNUSED,
568 StgBool revert_all STG_UNUSED) {
569 #if defined(STM_FG_LOCKS)
570 FOR_EACH_ENTRY(trec, e, {
571 if (revert_all || entry_is_update(e)) {
574 if (tvar_is_locked(s, trec)) {
575 unlock_tvar(trec, s, e -> expected_value, TRUE);
582 /*......................................................................*/
584 // validate_and_acquire_ownership : this performs the twin functions
585 // of checking that the TVars referred to by entries in trec hold the
586 // expected values and:
588 // - locking the TVar (on updated TVars during commit, or all TVars
591 // - recording the identity of the TRec who wrote the value seen in the
592 // TVar (on non-updated TVars during commit). These values are
593 // stashed in the TRec entries and are then checked in check_read_only
594 // to ensure that an atomic snapshot of all of these locations has been
597 static StgBool validate_and_acquire_ownership (StgTRecHeader *trec,
599 int retain_ownership) {
603 TRACE("%p : shake, pretending trec is invalid when it may not be\n", trec);
607 ASSERT ((trec -> state == TREC_ACTIVE) ||
608 (trec -> state == TREC_WAITING) ||
609 (trec -> state == TREC_CONDEMNED));
610 result = !((trec -> state) == TREC_CONDEMNED);
612 FOR_EACH_ENTRY(trec, e, {
615 if (acquire_all || entry_is_update(e)) {
616 TRACE("%p : trying to acquire %p\n", trec, s);
617 if (!cond_lock_tvar(trec, s, e -> expected_value)) {
618 TRACE("%p : failed to acquire %p\n", trec, s);
623 ASSERT(use_read_phase);
625 TRACE("%p : will need to check %p\n", trec, s);
626 if (s -> current_value != e -> expected_value) {
627 TRACE("%p : doesn't match\n", trec);
631 e -> saw_update_by = s -> last_update_by;
632 if (s -> current_value != e -> expected_value) {
633 TRACE("%p : doesn't match (race)\n", trec);
637 TRACE("%p : need to check update by %p\n", trec, e -> saw_update_by);
644 if ((!result) || (!retain_ownership)) {
645 revert_ownership(trec, acquire_all);
651 // check_read_only : check that we've seen an atomic snapshot of the
652 // non-updated TVars accessed by a trec. This checks that the last TRec to
653 // commit an update to the TVar is unchanged since the value was stashed in
654 // validate_and_acquire_ownership. If no udpate is seen to any TVar than
655 // all of them contained their expected values at the start of the call to
658 // The paper "Concurrent programming without locks" (under submission), or
659 // Keir Fraser's PhD dissertation "Practical lock-free programming" discuss
660 // this kind of algorithm.
662 static StgBool check_read_only(StgTRecHeader *trec STG_UNUSED) {
663 StgBool result = TRUE;
665 ASSERT (use_read_phase);
667 FOR_EACH_ENTRY(trec, e, {
670 if (entry_is_read_only(e)) {
671 TRACE("%p : check_read_only for TVar %p, saw %p\n", trec, s, e -> saw_update_by);
672 if (s -> last_update_by != e -> saw_update_by) {
673 // ||s -> current_value != e -> expected_value) {
674 TRACE("%p : mismatch\n", trec);
686 /************************************************************************/
688 void stmPreGCHook() {
690 TRACE("stmPreGCHook\n");
694 /************************************************************************/
697 TRACE("initSTM, NO_TREC=%p\n", NO_TREC);
700 /*......................................................................*/
702 StgTRecHeader *stmStartTransaction(StgRegTable *reg,
703 StgTRecHeader *outer) {
705 TRACE("%p : stmStartTransaction\n", outer);
706 t = new_stg_trec_header(reg, outer);
707 TRACE("%p : stmStartTransaction()=%p\n", outer, t);
711 /*......................................................................*/
713 void stmAbortTransaction(StgTRecHeader *trec) {
714 TRACE("%p : stmAbortTransaction\n", trec);
715 ASSERT (trec != NO_TREC);
716 ASSERT ((trec -> state == TREC_ACTIVE) ||
717 (trec -> state == TREC_WAITING) ||
718 (trec -> state == TREC_CONDEMNED));
721 if (trec -> state == TREC_WAITING) {
722 ASSERT (trec -> enclosing_trec == NO_TREC);
723 TRACE("%p : stmAbortTransaction aborting waiting transaction\n", trec);
724 remove_wait_queue_entries_for_trec(trec);
726 trec -> state = TREC_ABORTED;
729 TRACE("%p : stmAbortTransaction done\n", trec);
732 /*......................................................................*/
734 void stmCondemnTransaction(StgTRecHeader *trec) {
735 TRACE("%p : stmCondemnTransaction\n", trec);
736 ASSERT (trec != NO_TREC);
737 ASSERT ((trec -> state == TREC_ACTIVE) ||
738 (trec -> state == TREC_WAITING) ||
739 (trec -> state == TREC_CONDEMNED));
742 if (trec -> state == TREC_WAITING) {
743 ASSERT (trec -> enclosing_trec == NO_TREC);
744 TRACE("%p : stmCondemnTransaction condemning waiting transaction\n", trec);
745 remove_wait_queue_entries_for_trec(trec);
747 trec -> state = TREC_CONDEMNED;
750 TRACE("%p : stmCondemnTransaction done\n", trec);
753 /*......................................................................*/
755 StgTRecHeader *stmGetEnclosingTRec(StgTRecHeader *trec) {
756 StgTRecHeader *outer;
757 TRACE("%p : stmGetEnclosingTRec\n", trec);
758 outer = trec -> enclosing_trec;
759 TRACE("%p : stmGetEnclosingTRec()=%p\n", trec, outer);
763 /*......................................................................*/
765 StgBool stmValidateNestOfTransactions(StgTRecHeader *trec) {
769 TRACE("%p : stmValidateNestOfTransactions\n", trec);
770 ASSERT(trec != NO_TREC);
771 ASSERT((trec -> state == TREC_ACTIVE) ||
772 (trec -> state == TREC_WAITING) ||
773 (trec -> state == TREC_CONDEMNED));
779 while (t != NO_TREC) {
780 result &= validate_and_acquire_ownership(t, TRUE, FALSE);
781 t = t -> enclosing_trec;
784 if (!result && trec -> state != TREC_WAITING) {
785 trec -> state = TREC_CONDEMNED;
790 TRACE("%p : stmValidateNestOfTransactions()=%d\n", trec, result);
794 /*......................................................................*/
796 StgBool stmCommitTransaction(StgRegTable *reg STG_UNUSED, StgTRecHeader *trec) {
798 TRACE("%p : stmCommitTransaction()\n", trec);
799 ASSERT (trec != NO_TREC);
800 ASSERT (trec -> enclosing_trec == NO_TREC);
801 ASSERT ((trec -> state == TREC_ACTIVE) ||
802 (trec -> state == TREC_CONDEMNED));
805 result = validate_and_acquire_ownership(trec, (!use_read_phase), TRUE);
807 // We now know that all the updated locations hold their expected values.
808 ASSERT (trec -> state == TREC_ACTIVE);
810 if (use_read_phase) {
811 TRACE("%p : doing read check\n", trec);
812 result = check_read_only(trec);
813 TRACE("%p : read-check %s\n", trec, result ? "succeeded" : "failed");
817 // We now know that all of the read-only locations held their exepcted values
818 // at the end of the call to validate_and_acquire_ownership. This forms the
819 // linearization point of the commit.
821 FOR_EACH_ENTRY(trec, e, {
824 if (e -> new_value != e -> expected_value) {
825 // Entry is an update: write the value back to the TVar, unlocking it if
828 ACQ_ASSERT(tvar_is_locked(s, trec));
829 TRACE("%p : writing %p to %p, waking waiters\n", trec, e -> new_value, s);
830 unpark_waiters_on(s);
832 s -> last_update_by = trec;
834 unlock_tvar(trec, s, e -> new_value, TRUE);
836 ACQ_ASSERT(!tvar_is_locked(s, trec));
839 revert_ownership(trec, FALSE);
845 TRACE("%p : stmCommitTransaction()=%d\n", trec, result);
850 /*......................................................................*/
852 StgBool stmCommitNestedTransaction(StgRegTable *reg, StgTRecHeader *trec) {
855 ASSERT (trec != NO_TREC && trec -> enclosing_trec != NO_TREC);
856 TRACE("%p : stmCommitNestedTransaction() into %p\n", trec, trec -> enclosing_trec);
857 ASSERT ((trec -> state == TREC_ACTIVE) || (trec -> state == TREC_CONDEMNED));
861 et = trec -> enclosing_trec;
862 result = validate_and_acquire_ownership(trec, FALSE, TRUE);
864 // We now know that all the updated locations hold their expected values.
866 if (use_read_phase) {
867 TRACE("%p : doing read check\n", trec);
868 result = check_read_only(trec);
871 // We now know that all of the read-only locations held their exepcted values
872 // at the end of the call to validate_and_acquire_ownership. This forms the
873 // linearization point of the commit.
876 TRACE("%p : read-check succeeded\n", trec);
877 FOR_EACH_ENTRY(trec, e, {
878 // Merge each entry into the enclosing transaction record, release all
883 if (entry_is_update(e)) {
884 unlock_tvar(trec, s, e -> expected_value, FALSE);
886 merge_update_into(reg, et, s, e -> expected_value, e -> new_value);
887 ACQ_ASSERT(s -> current_value != trec);
890 revert_ownership(trec, FALSE);
897 TRACE("%p : stmCommitNestedTransaction()=%d\n", trec, result);
902 /*......................................................................*/
904 StgBool stmWait(StgRegTable *reg, StgTSO *tso, StgTRecHeader *trec) {
906 TRACE("%p : stmWait(%p)\n", trec, tso);
907 ASSERT (trec != NO_TREC);
908 ASSERT (trec -> enclosing_trec == NO_TREC);
909 ASSERT ((trec -> state == TREC_ACTIVE) ||
910 (trec -> state == TREC_CONDEMNED));
913 result = validate_and_acquire_ownership(trec, TRUE, TRUE);
915 // The transaction is valid so far so we can actually start waiting.
916 // (Otherwise the transaction was not valid and the thread will have to
919 // Put ourselves to sleep. We retain locks on all the TVars involved
920 // until we are sound asleep : (a) on the wait queues, (b) BlockedOnSTM
921 // in the TSO, (c) TREC_WAITING in the Trec.
922 build_wait_queue_entries_for_trec(reg, tso, trec);
924 trec -> state = TREC_WAITING;
926 // As soon as we start releasing ownership, another thread may find us
927 // and wake us up. This may happen even before we have finished
928 // releasing ownership.
929 revert_ownership(trec, TRUE);
934 TRACE("%p : stmWait(%p)=%d\n", trec, tso, result);
938 /*......................................................................*/
940 StgBool stmReWait(StgTSO *tso) {
942 StgTRecHeader *trec = tso->trec;
944 TRACE("%p : stmReWait\n", trec);
945 ASSERT (trec != NO_TREC);
946 ASSERT (trec -> enclosing_trec == NO_TREC);
947 ASSERT ((trec -> state == TREC_WAITING) ||
948 (trec -> state == TREC_CONDEMNED));
951 result = validate_and_acquire_ownership(trec, TRUE, TRUE);
952 TRACE("%p : validation %s\n", trec, result ? "succeeded" : "failed");
954 // The transaction remains valid -- do nothing because it is already on
956 ASSERT (trec -> state == TREC_WAITING);
958 revert_ownership(trec, TRUE);
960 // The transcation has become invalid. We can now remove it from the wait
962 if (trec -> state != TREC_CONDEMNED) {
963 remove_wait_queue_entries_for_trec (trec);
969 TRACE("%p : stmReWait()=%d\n", trec, result);
973 /*......................................................................*/
975 static TRecEntry *get_entry_for(StgTRecHeader *trec, StgTVar *tvar, StgTRecHeader **in) {
976 TRecEntry *result = NULL;
978 TRACE("%p : get_entry_for TVar %p\n", trec, tvar);
979 ASSERT(trec != NO_TREC);
982 FOR_EACH_ENTRY(trec, e, {
983 if (e -> tvar == tvar) {
991 trec = trec -> enclosing_trec;
992 } while (result == NULL && trec != NO_TREC);
997 static StgClosure *read_current_value(StgTRecHeader *trec STG_UNUSED, StgTVar *tvar) {
999 result = tvar -> current_value;
1001 #if defined(STM_FG_LOCKS)
1002 while (GET_INFO(result) == &stg_TREC_HEADER_info) {
1003 TRACE("%p : read_current_value(%p) saw %p\n", trec, tvar, result);
1004 result = tvar -> current_value;
1008 TRACE("%p : read_current_value(%p)=%p\n", trec, tvar, result);
1012 /*......................................................................*/
1014 StgClosure *stmReadTVar(StgRegTable *reg,
1015 StgTRecHeader *trec,
1017 StgTRecHeader *entry_in;
1018 StgClosure *result = NULL;
1019 TRecEntry *entry = NULL;
1020 TRACE("%p : stmReadTVar(%p)\n", trec, tvar);
1021 ASSERT (trec != NO_TREC);
1022 ASSERT (trec -> state == TREC_ACTIVE ||
1023 trec -> state == TREC_CONDEMNED);
1025 entry = get_entry_for(trec, tvar, &entry_in);
1027 if (entry != NULL) {
1028 if (entry_in == trec) {
1029 // Entry found in our trec
1030 result = entry -> new_value;
1032 // Entry found in another trec
1033 TRecEntry *new_entry = get_new_entry(reg, trec);
1034 new_entry -> tvar = tvar;
1035 new_entry -> expected_value = entry -> expected_value;
1036 new_entry -> new_value = entry -> new_value;
1037 result = new_entry -> new_value;
1041 StgClosure *current_value = read_current_value(trec, tvar);
1042 TRecEntry *new_entry = get_new_entry(reg, trec);
1043 new_entry -> tvar = tvar;
1044 new_entry -> expected_value = current_value;
1045 new_entry -> new_value = current_value;
1046 result = current_value;
1049 TRACE("%p : stmReadTVar(%p)=%p\n", trec, tvar, result);
1053 /*......................................................................*/
1055 void stmWriteTVar(StgRegTable *reg,
1056 StgTRecHeader *trec,
1058 StgClosure *new_value) {
1060 StgTRecHeader *entry_in;
1061 TRecEntry *entry = NULL;
1062 TRACE("%p : stmWriteTVar(%p, %p)\n", trec, tvar, new_value);
1063 ASSERT (trec != NO_TREC);
1064 ASSERT (trec -> state == TREC_ACTIVE ||
1065 trec -> state == TREC_CONDEMNED);
1067 entry = get_entry_for(trec, tvar, &entry_in);
1069 if (entry != NULL) {
1070 if (entry_in == trec) {
1071 // Entry found in our trec
1072 entry -> new_value = new_value;
1074 // Entry found in another trec
1075 TRecEntry *new_entry = get_new_entry(reg, trec);
1076 new_entry -> tvar = tvar;
1077 new_entry -> expected_value = entry -> expected_value;
1078 new_entry -> new_value = new_value;
1082 StgClosure *current_value = read_current_value(trec, tvar);
1083 TRecEntry *new_entry = get_new_entry(reg, trec);
1084 new_entry -> tvar = tvar;
1085 new_entry -> expected_value = current_value;
1086 new_entry -> new_value = new_value;
1089 TRACE("%p : stmWriteTVar done\n", trec);
1092 /*......................................................................*/
1094 StgTVar *stmNewTVar(StgRegTable *reg,
1095 StgClosure *new_value) {
1097 result = new_tvar(reg, new_value);
1101 /*......................................................................*/