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.
47 /*----------------------------------------------------------------------
53 extern void stmPreGCHook(void);
55 /*----------------------------------------------------------------------
57 Transaction context management
58 ------------------------------
62 /* Create and enter a new transaction context */
64 extern StgTRecHeader *stmStartTransaction(Capability *cap, StgTRecHeader *outer);
65 extern StgTRecHeader *stmStartNestedTransaction(Capability *cap, StgTRecHeader *outer
69 * Exit the current transaction context, abandoning any read/write
70 * operations performed within it and removing the thread from any
71 * tvar wait queues if it was waitin. Note that if nested transactions
72 * are not fully supported then this may leave the enclosing
73 * transaction contexts doomed to abort.
76 extern void stmAbortTransaction(Capability *cap, StgTRecHeader *trec);
79 * Ensure that a subsequent commit / validation will fail. We use this
80 * in our current handling of transactions that may have become invalid
81 * and started looping. We strip their stack back to the ATOMICALLY_FRAME,
82 * and, when the thread is next scheduled, discover it to be invalid and
83 * re-execute it. However, we need to force the transaction to stay invalid
84 * in case other threads' updates make it valid in the mean time.
87 extern void stmCondemnTransaction(Capability *cap, StgTRecHeader *trec);
90 * Return the trec within which the specified trec was created (not
91 * valid if trec==NO_TREC).
94 extern StgTRecHeader *stmGetEnclosingTRec(StgTRecHeader *trec);
96 /*----------------------------------------------------------------------
101 Test whether the specified transaction record, and all those within which
102 it is nested, are still valid.
104 Note: the caller can assume that once stmValidateTransaction has
105 returned FALSE for a given trec then that transaction will never
106 again be valid -- we rely on this in Schedule.c when kicking invalid
107 threads at GC (in case they are stuck looping)
110 extern StgBool stmValidateNestOfTransactions(StgTRecHeader *trec);
112 /*----------------------------------------------------------------------
114 Commit/wait/rewait operations
115 -----------------------------
117 These four operations return boolean results which should be interpreted
120 true => The transaction record was definitely valid
122 false => The transaction record may not have been valid
124 Note that, for nested operations, validity here is solely in terms
125 of the specified trec: it does not say whether those that it may be
126 nested are themselves valid. Callers can check this with
127 stmValidateNestOfTransactions.
129 The user of the STM should ensure that it is always safe to assume that a
130 transaction context is not valid when in fact it is (i.e. to return false in
131 place of true, with side-effects as defined below). This may cause
132 needless retries of transactions (in the case of validate and commit), or it
133 may cause needless spinning instead of blocking (in the case of wait and
136 In defining the behaviour of wait and rewait we distinguish between two
137 different aspects of a thread's runnability:
139 - We say that a thread is "blocked" when it is not running or
140 runnable as far as the scheduler is concerned.
142 - We say that a thread is "waiting" when its StgTRecHeader is linked on an
145 Considering only STM operations, (blocked) => (waiting). The user of the STM
146 should ensure that they are prepared for threads to be unblocked spuriously
147 and for wait/reWait to return false even when the previous transaction context
148 is actually still valid.
152 * Test whether the current transaction context is valid and, if so,
153 * commit its memory accesses to the heap. stmCommitTransaction must
154 * unblock any threads which are waiting on tvars that updates have
158 extern StgBool stmCommitTransaction(Capability *cap, StgTRecHeader *trec);
159 extern StgBool stmCommitNestedTransaction(Capability *cap, StgTRecHeader *trec);
162 * Test whether the current transaction context is valid and, if so,
163 * start the thread waiting for updates to any of the tvars it has
164 * ready from and mark it as blocked. It is an error to call stmWait
165 * if the thread is already waiting.
168 extern StgBool stmWait(Capability *cap,
170 StgTRecHeader *trec);
172 extern void stmWaitUnlock(Capability *cap, StgTRecHeader *trec);
175 * Test whether the current transaction context is valid and, if so,
176 * leave the thread waiting and mark it as blocked again. If the
177 * transaction context is no longer valid then stop the thread waiting
178 * and leave it as unblocked. It is an error to call stmReWait if the
179 * thread is not waiting.
182 extern StgBool stmReWait(Capability *cap, StgTSO *tso);
184 /*----------------------------------------------------------------------
186 TVar management operations
187 --------------------------
190 extern StgTVar *stmNewTVar(Capability *cap,
191 StgClosure *new_value);
193 /*----------------------------------------------------------------------
195 Data access operations
196 ----------------------
200 * Return the logical contents of 'tvar' within the context of the
201 * thread's current transaction.
204 extern StgClosure *stmReadTVar(Capability *cap,
208 /* Update the logical contents of 'tvar' within the context of the
209 * thread's current transaction.
212 extern void stmWriteTVar(Capability *cap,
215 StgClosure *new_value);
217 /*----------------------------------------------------------------------*/
221 #define END_STM_WAIT_QUEUE ((StgTVarWaitQueue *)(void *)&stg_END_STM_WAIT_QUEUE_closure)
222 #define END_STM_CHUNK_LIST ((StgTRecChunk *)(void *)&stg_END_STM_CHUNK_LIST_closure)
224 #define NO_TREC ((StgTRecHeader *)(void *)&stg_NO_TREC_closure)
226 /*----------------------------------------------------------------------*/