1 /*----------------------------------------------------------------------
3 * (c) The GHC Team, 1998-2004
5 * STM interface definition
7 *----------------------------------------------------------------------
9 STM.h defines the C-level interface to the STM.
11 The design follows that of the PPoPP 2005 paper "Composable memory
12 transactions" extended to include fine-grained locking of TVars.
14 Three different implementations can be built. In overview:
16 STM_UNIPROC -- no locking at all: not safe for concurrent invocations
18 STM_CG_LOCK -- coarse-grained locking : a single mutex protects all
21 STM_FG_LOCKS -- per-TVar exclusion : each TVar can be owned by at
22 most one TRec at any time. This allows dynamically
23 non-conflicting transactions to commit in parallel.
24 The implementation treats reads optimisitcally --
25 extra versioning information is retained in the
26 saw_update_by field of the TVars so that they do not
27 need to be locked for reading.
29 STM.C contains more details about the locking schemes used.
45 /*----------------------------------------------------------------------
51 void stmPreGCHook(void);
53 /*----------------------------------------------------------------------
55 Transaction context management
56 ------------------------------
60 /* Create and enter a new transaction context */
62 StgTRecHeader *stmStartTransaction(Capability *cap, StgTRecHeader *outer);
63 StgTRecHeader *stmStartNestedTransaction(Capability *cap, StgTRecHeader *outer
67 * Roll back the current transatcion context. NB: if this is a nested tx
68 * then we merge its read set into its parents. This is because a change
69 * to that read set could change whether or not the tx should abort.
72 void stmAbortTransaction(Capability *cap, StgTRecHeader *trec);
73 void stmFreeAbortedTRec(Capability *cap, StgTRecHeader *trec);
76 * Ensure that a subsequent commit / validation will fail. We use this
77 * in our current handling of transactions that may have become invalid
78 * and started looping. We strip their stack back to the ATOMICALLY_FRAME,
79 * and, when the thread is next scheduled, discover it to be invalid and
80 * re-execute it. However, we need to force the transaction to stay invalid
81 * in case other threads' updates make it valid in the mean time.
84 void stmCondemnTransaction(Capability *cap, StgTRecHeader *trec);
87 * Return the trec within which the specified trec was created (not
88 * valid if trec==NO_TREC).
91 StgTRecHeader *stmGetEnclosingTRec(StgTRecHeader *trec);
93 /*----------------------------------------------------------------------
98 Test whether the specified transaction record, and all those within which
99 it is nested, are still valid.
101 Note: the caller can assume that once stmValidateTransaction has
102 returned FALSE for a given trec then that transaction will never
103 again be valid -- we rely on this in Schedule.c when kicking invalid
104 threads at GC (in case they are stuck looping)
107 StgBool stmValidateNestOfTransactions(StgTRecHeader *trec);
109 /*----------------------------------------------------------------------
111 Commit/wait/rewait operations
112 -----------------------------
114 These four operations return boolean results which should be interpreted
117 true => The transaction record was definitely valid
119 false => The transaction record may not have been valid
121 Note that, for nested operations, validity here is solely in terms
122 of the specified trec: it does not say whether those that it may be
123 nested are themselves valid. Callers can check this with
124 stmValidateNestOfTransactions.
126 The user of the STM should ensure that it is always safe to assume that a
127 transaction context is not valid when in fact it is (i.e. to return false in
128 place of true, with side-effects as defined below). This may cause
129 needless retries of transactions (in the case of validate and commit), or it
130 may cause needless spinning instead of blocking (in the case of wait and
133 In defining the behaviour of wait and rewait we distinguish between two
134 different aspects of a thread's runnability:
136 - We say that a thread is "blocked" when it is not running or
137 runnable as far as the scheduler is concerned.
139 - We say that a thread is "waiting" when its StgTRecHeader is linked on an
142 Considering only STM operations, (blocked) => (waiting). The user of the STM
143 should ensure that they are prepared for threads to be unblocked spuriously
144 and for wait/reWait to return false even when the previous transaction context
145 is actually still valid.
149 * Fill in the trec's list of invariants that might be violated by the current
153 StgInvariantCheckQueue *stmGetInvariantsToCheck(Capability *cap,
154 StgTRecHeader *trec);
156 void stmAddInvariantToCheck(Capability *cap,
161 * Test whether the current transaction context is valid and, if so,
162 * commit its memory accesses to the heap. stmCommitTransaction must
163 * unblock any threads which are waiting on tvars that updates have
167 StgBool stmCommitTransaction(Capability *cap, StgTRecHeader *trec);
168 StgBool stmCommitNestedTransaction(Capability *cap, StgTRecHeader *trec);
171 * Test whether the current transaction context is valid and, if so,
172 * start the thread waiting for updates to any of the tvars it has
173 * ready from and mark it as blocked. It is an error to call stmWait
174 * if the thread is already waiting.
177 StgBool stmWait(Capability *cap, StgTSO *tso, StgTRecHeader *trec);
179 void stmWaitUnlock(Capability *cap, StgTRecHeader *trec);
182 * Test whether the current transaction context is valid and, if so,
183 * leave the thread waiting and mark it as blocked again. If the
184 * transaction context is no longer valid then stop the thread waiting
185 * and leave it as unblocked. It is an error to call stmReWait if the
186 * thread is not waiting.
189 StgBool stmReWait(Capability *cap, StgTSO *tso);
191 /*----------------------------------------------------------------------
193 TVar management operations
194 --------------------------
197 StgTVar *stmNewTVar(Capability *cap, StgClosure *new_value);
199 /*----------------------------------------------------------------------
201 Data access operations
202 ----------------------
206 * Return the logical contents of 'tvar' within the context of the
207 * thread's current transaction.
210 StgClosure *stmReadTVar(Capability *cap,
214 /* Update the logical contents of 'tvar' within the context of the
215 * thread's current transaction.
218 void stmWriteTVar(Capability *cap,
221 StgClosure *new_value);
223 /*----------------------------------------------------------------------*/
227 #define END_STM_WATCH_QUEUE ((StgTVarWatchQueue *)(void *)&stg_END_STM_WATCH_QUEUE_closure)
228 #define END_INVARIANT_CHECK_QUEUE ((StgInvariantCheckQueue *)(void *)&stg_END_INVARIANT_CHECK_QUEUE_closure)
229 #define END_STM_CHUNK_LIST ((StgTRecChunk *)(void *)&stg_END_STM_CHUNK_LIST_closure)
231 #define NO_TREC ((StgTRecHeader *)(void *)&stg_NO_TREC_closure)
233 /*----------------------------------------------------------------------*/