1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 2001-2006
7 * The notion of a capability is used when operating in multi-threaded
8 * environments (which the THREADED_RTS build of the RTS does), to
9 * hold all the state an OS thread/task needs to run Haskell code:
10 * its STG registers, a pointer to its TSO, a nursery etc. During
11 * STG execution, a pointer to the capabilitity is kept in a
14 * Only in an THREADED_RTS build will there be multiple capabilities,
15 * in the non-threaded builds there is one global capability, namely
18 * This header file contains the functions for working with capabilities.
19 * (the main, and only, consumer of this interface is the scheduler).
21 * --------------------------------------------------------------------------*/
31 // State required by the STG virtual machine when running Haskell
32 // code. During STG execution, the BaseReg register always points
33 // to the StgRegTable of the current Capability (&cap->r).
37 nat no; // capability number.
39 // The Task currently holding this Capability. This task has
40 // exclusive access to the contents of this Capability (apart from
41 // returning_tasks_hd/returning_tasks_tl).
42 // Locks required: cap->lock.
45 // true if this Capability is running Haskell code, used for
46 // catching unsafe call-ins.
49 // true if this Capability is currently in the GC
52 // The run queue. The Task owning this Capability has exclusive
53 // access to its run queue, so can wake up threads without
54 // taking a lock, and the common path through the scheduler is
59 // Tasks currently making safe foreign calls. Doubly-linked.
60 // When returning, a task first acquires the Capability before
61 // removing itself from this list, so that the GC can find all
62 // the suspended TSOs easily. Hence, when migrating a Task from
63 // the returning_tasks list, we must also migrate its entry from
65 Task *suspended_ccalling_tasks;
67 // One mutable list per generation, so we don't need to take any
68 // locks when updating an old-generation thunk. These
69 // mini-mut-lists are moved onto the respective gen->mut_list at
73 // Context switch flag. We used to have one global flag, now one
74 // per capability. Locks required : none (conflicts are harmless)
77 #if defined(THREADED_RTS)
78 // Worker Tasks waiting in the wings. Singly-linked.
81 // This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
84 // Tasks waiting to return from a foreign call, or waiting to make
85 // a new call-in using this Capability (NULL if empty).
86 // NB. this field needs to be modified by tasks other than the
87 // running_task, so it requires cap->lock to modify. A task can
88 // check whether it is NULL without taking the lock, however.
89 Task *returning_tasks_hd; // Singly-linked, with head/tail
90 Task *returning_tasks_tl;
92 // A list of threads to append to this Capability's run queue at
93 // the earliest opportunity. These are threads that have been
94 // woken up by another Capability.
95 StgTSO *wakeup_queue_hd;
96 StgTSO *wakeup_queue_tl;
100 // Stats on spark creation/conversion
102 nat sparks_converted;
106 // Per-capability STM-related data
107 StgTVarWatchQueue *free_tvar_watch_queues;
108 StgInvariantCheckQueue *free_invariant_check_queues;
109 StgTRecChunk *free_trec_chunks;
110 StgTRecHeader *free_trec_headers;
111 nat transaction_tokens;
112 } // typedef Capability is defined in RtsAPI.h
113 // Capabilities are stored in an array, so make sure that adjacent
114 // Capabilities don't share any cache-lines:
115 #ifndef mingw32_HOST_OS
116 ATTRIBUTE_ALIGNED(64)
121 #if defined(THREADED_RTS)
122 #define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
124 #define ASSERT_TASK_ID(task) /*empty*/
127 // These properties should be true when a Task is holding a Capability
128 #define ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task) \
129 ASSERT(cap->running_task != NULL && cap->running_task == task); \
130 ASSERT(task->cap == cap); \
131 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task)
133 // Sometimes a Task holds a Capability, but the Task is not associated
134 // with that Capability (ie. task->cap != cap). This happens when
135 // (a) a Task holds multiple Capabilities, and (b) when the current
136 // Task is bound, its thread has just blocked, and it may have been
137 // moved to another Capability.
138 #define ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task) \
139 ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
140 cap->run_queue_tl == END_TSO_QUEUE : 1); \
141 ASSERT(myTask() == task); \
142 ASSERT_TASK_ID(task);
144 // Converts a *StgRegTable into a *Capability.
146 INLINE_HEADER Capability *
147 regTableToCapability (StgRegTable *reg)
149 return (Capability *)((void *)((unsigned char*)reg - FIELD_OFFSET(Capability,r)));
152 // Initialise the available capabilities.
154 void initCapabilities (void);
156 // Release a capability. This is called by a Task that is exiting
157 // Haskell to make a foreign call, or in various other cases when we
158 // want to relinquish a Capability that we currently hold.
160 // ASSUMES: cap->running_task is the current Task.
162 #if defined(THREADED_RTS)
163 void releaseCapability (Capability* cap);
164 void releaseAndWakeupCapability (Capability* cap);
165 void releaseCapability_ (Capability* cap, rtsBool always_wakeup);
166 // assumes cap->lock is held
168 // releaseCapability() is empty in non-threaded RTS
169 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
170 INLINE_HEADER void releaseAndWakeupCapability (Capability* cap STG_UNUSED) {};
171 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED,
172 rtsBool always_wakeup STG_UNUSED) {};
176 // one global capability
177 extern Capability MainCapability;
180 // Array of all the capabilities
182 extern nat n_capabilities;
183 extern Capability *capabilities;
185 // The Capability that was last free. Used as a good guess for where
186 // to assign new threads.
188 extern Capability *last_free_capability;
190 // GC indicator, in scope for the scheduler
191 #define PENDING_GC_SEQ 1
192 #define PENDING_GC_PAR 2
193 extern volatile StgWord waiting_for_gc;
195 // Acquires a capability at a return point. If *cap is non-NULL, then
196 // this is taken as a preference for the Capability we wish to
199 // OS threads waiting in this function get priority over those waiting
200 // in waitForCapability().
202 // On return, *cap is non-NULL, and points to the Capability acquired.
204 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
206 INLINE_HEADER void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
208 #if defined(THREADED_RTS)
210 // Gives up the current capability IFF there is a higher-priority
211 // thread waiting for it. This happens in one of two ways:
213 // (a) we are passing the capability to another OS thread, so
214 // that it can run a bound Haskell thread, or
216 // (b) there is an OS thread waiting to return from a foreign call
218 // On return: *pCap is NULL if the capability was released. The
219 // current task should then re-acquire it using waitForCapability().
221 void yieldCapability (Capability** pCap, Task *task);
223 // Acquires a capability for doing some work.
225 // On return: pCap points to the capability.
227 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
229 // Wakes up a thread on a Capability (probably a different Capability
230 // from the one held by the current Task).
232 void wakeupThreadOnCapability (Capability *my_cap, Capability *other_cap,
235 // Wakes up a worker thread on just one Capability, used when we
236 // need to service some global event.
238 void prodOneCapability (void);
239 void prodCapability (Capability *cap, Task *task);
241 // Similar to prodOneCapability(), but prods all of them.
243 void prodAllCapabilities (void);
245 // Waits for a capability to drain of runnable threads and workers,
246 // and then acquires it. Used at shutdown time.
248 void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
250 // Attempt to gain control of a Capability if it is free.
252 rtsBool tryGrabCapability (Capability *cap, Task *task);
254 // Try to find a spark to run
256 StgClosure *findSpark (Capability *cap);
258 // True if any capabilities have sparks
260 rtsBool anySparks (void);
262 INLINE_HEADER rtsBool emptySparkPoolCap (Capability *cap);
263 INLINE_HEADER nat sparkPoolSizeCap (Capability *cap);
264 INLINE_HEADER void discardSparksCap (Capability *cap);
266 #else // !THREADED_RTS
268 // Grab a capability. (Only in the non-threaded RTS; in the threaded
269 // RTS one of the waitFor*Capability() functions must be used).
271 extern void grabCapability (Capability **pCap);
273 #endif /* !THREADED_RTS */
275 // cause all capabilities to context switch as soon as possible.
276 void setContextSwitches(void);
278 // Free all capabilities
279 void freeCapabilities (void);
282 void markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
283 rtsBool prune_sparks);
284 void markCapabilities (evac_fn evac, void *user);
285 void traverseSparkQueues (evac_fn evac, void *user);
287 /* -----------------------------------------------------------------------------
288 * INLINE functions... private below here
289 * -------------------------------------------------------------------------- */
292 recordMutableCap (StgClosure *p, Capability *cap, nat gen)
296 // We must own this Capability in order to modify its mutable list.
297 ASSERT(cap->running_task == myTask());
298 bd = cap->mut_lists[gen];
299 if (bd->free >= bd->start + BLOCK_SIZE_W) {
301 new_bd = allocBlock_lock();
304 cap->mut_lists[gen] = bd;
306 *bd->free++ = (StgWord)p;
309 #if defined(THREADED_RTS)
310 INLINE_HEADER rtsBool
311 emptySparkPoolCap (Capability *cap)
312 { return looksEmpty(cap->sparks); }
315 sparkPoolSizeCap (Capability *cap)
316 { return sparkPoolSize(cap->sparks); }
319 discardSparksCap (Capability *cap)
320 { return discardSparks(cap->sparks); }
323 #endif /* CAPABILITY_H */