1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 2001-2006
7 * For details on the high-level design, see
8 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Scheduler
10 * A Capability holds all the state an OS thread/task needs to run
11 * Haskell code: its STG registers, a pointer to its TSO, a nursery
12 * etc. During STG execution, a pointer to the Capabilitity is kept in
13 * a register (BaseReg).
15 * Only in a THREADED_RTS build will there be multiple capabilities,
16 * in the non-threaded RTS there is one global capability, called
19 * --------------------------------------------------------------------------*/
24 #include "sm/GC.h" // for evac_fn
28 #include "BeginPrivate.h"
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 // The run queue. The Task owning this Capability has exclusive
50 // access to its run queue, so can wake up threads without
51 // taking a lock, and the common path through the scheduler is
56 // Tasks currently making safe foreign calls. Doubly-linked.
57 // When returning, a task first acquires the Capability before
58 // removing itself from this list, so that the GC can find all
59 // the suspended TSOs easily. Hence, when migrating a Task from
60 // the returning_tasks list, we must also migrate its entry from
62 InCall *suspended_ccalls;
64 // One mutable list per generation, so we don't need to take any
65 // locks when updating an old-generation thunk. This also lets us
66 // keep track of which closures this CPU has been mutating, so we
67 // can traverse them using the right thread during GC and avoid
68 // unnecessarily moving the data from one cache to another.
70 bdescr **saved_mut_lists; // tmp use during GC
72 // block for allocating pinned objects into
73 bdescr *pinned_object_block;
75 // Context switch flag. We used to have one global flag, now one
76 // per capability. Locks required : none (conflicts are harmless)
79 #if defined(THREADED_RTS)
80 // Worker Tasks waiting in the wings. Singly-linked.
83 // This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
86 // Tasks waiting to return from a foreign call, or waiting to make
87 // a new call-in using this Capability (NULL if empty).
88 // NB. this field needs to be modified by tasks other than the
89 // running_task, so it requires cap->lock to modify. A task can
90 // check whether it is NULL without taking the lock, however.
91 Task *returning_tasks_hd; // Singly-linked, with head/tail
92 Task *returning_tasks_tl;
94 // Messages, or END_TSO_QUEUE.
99 // Stats on spark creation/conversion
101 nat sparks_converted;
105 // Per-capability STM-related data
106 StgTVarWatchQueue *free_tvar_watch_queues;
107 StgInvariantCheckQueue *free_invariant_check_queues;
108 StgTRecChunk *free_trec_chunks;
109 StgTRecHeader *free_trec_headers;
110 nat transaction_tokens;
111 } // typedef Capability is defined in RtsAPI.h
112 // Capabilities are stored in an array, so make sure that adjacent
113 // Capabilities don't share any cache-lines:
114 #ifndef mingw32_HOST_OS
115 ATTRIBUTE_ALIGNED(64)
120 #if defined(THREADED_RTS)
121 #define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
123 #define ASSERT_TASK_ID(task) /*empty*/
126 // These properties should be true when a Task is holding a Capability
127 #define ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task) \
128 ASSERT(cap->running_task != NULL && cap->running_task == task); \
129 ASSERT(task->cap == cap); \
130 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task)
132 // Sometimes a Task holds a Capability, but the Task is not associated
133 // with that Capability (ie. task->cap != cap). This happens when
134 // (a) a Task holds multiple Capabilities, and (b) when the current
135 // Task is bound, its thread has just blocked, and it may have been
136 // moved to another Capability.
137 #define ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task) \
138 ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
139 cap->run_queue_tl == END_TSO_QUEUE : 1); \
140 ASSERT(myTask() == task); \
141 ASSERT_TASK_ID(task);
143 // Converts a *StgRegTable into a *Capability.
145 INLINE_HEADER Capability *
146 regTableToCapability (StgRegTable *reg)
148 return (Capability *)((void *)((unsigned char*)reg - STG_FIELD_OFFSET(Capability,r)));
151 // Initialise the available capabilities.
153 void initCapabilities (void);
155 // Release a capability. This is called by a Task that is exiting
156 // Haskell to make a foreign call, or in various other cases when we
157 // want to relinquish a Capability that we currently hold.
159 // ASSUMES: cap->running_task is the current Task.
161 #if defined(THREADED_RTS)
162 void releaseCapability (Capability* cap);
163 void releaseAndWakeupCapability (Capability* cap);
164 void releaseCapability_ (Capability* cap, rtsBool always_wakeup);
165 // assumes cap->lock is held
167 // releaseCapability() is empty in non-threaded RTS
168 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
169 INLINE_HEADER void releaseAndWakeupCapability (Capability* cap STG_UNUSED) {};
170 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED,
171 rtsBool always_wakeup STG_UNUSED) {};
174 // declared in includes/rts/Threads.h:
175 // extern Capability MainCapability;
177 // declared in includes/rts/Threads.h:
178 // extern nat n_capabilities;
180 // Array of all the capabilities
182 extern Capability *capabilities;
184 // The Capability that was last free. Used as a good guess for where
185 // to assign new threads.
187 extern Capability *last_free_capability;
189 // GC indicator, in scope for the scheduler
190 #define PENDING_GC_SEQ 1
191 #define PENDING_GC_PAR 2
192 extern volatile StgWord waiting_for_gc;
194 // Acquires a capability at a return point. If *cap is non-NULL, then
195 // this is taken as a preference for the Capability we wish to
198 // OS threads waiting in this function get priority over those waiting
199 // in waitForCapability().
201 // On return, *cap is non-NULL, and points to the Capability acquired.
203 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
205 EXTERN_INLINE void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
207 EXTERN_INLINE void recordClosureMutated (Capability *cap, StgClosure *p);
209 #if defined(THREADED_RTS)
211 // Gives up the current capability IFF there is a higher-priority
212 // thread waiting for it. This happens in one of two ways:
214 // (a) we are passing the capability to another OS thread, so
215 // that it can run a bound Haskell thread, or
217 // (b) there is an OS thread waiting to return from a foreign call
219 // On return: *pCap is NULL if the capability was released. The
220 // current task should then re-acquire it using waitForCapability().
222 void yieldCapability (Capability** pCap, Task *task);
224 // Acquires a capability for doing some work.
226 // On return: pCap points to the capability.
228 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
230 // Wakes up a worker thread on just one Capability, used when we
231 // need to service some global event.
233 void prodOneCapability (void);
234 void prodCapability (Capability *cap, Task *task);
236 // Similar to prodOneCapability(), but prods all of them.
238 void prodAllCapabilities (void);
240 // Waits for a capability to drain of runnable threads and workers,
241 // and then acquires it. Used at shutdown time.
243 void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
245 // Attempt to gain control of a Capability if it is free.
247 rtsBool tryGrabCapability (Capability *cap, Task *task);
249 // Try to find a spark to run
251 StgClosure *findSpark (Capability *cap);
253 // True if any capabilities have sparks
255 rtsBool anySparks (void);
257 INLINE_HEADER rtsBool emptySparkPoolCap (Capability *cap);
258 INLINE_HEADER nat sparkPoolSizeCap (Capability *cap);
259 INLINE_HEADER void discardSparksCap (Capability *cap);
261 #else // !THREADED_RTS
263 // Grab a capability. (Only in the non-threaded RTS; in the threaded
264 // RTS one of the waitFor*Capability() functions must be used).
266 extern void grabCapability (Capability **pCap);
268 #endif /* !THREADED_RTS */
270 // cause all capabilities to context switch as soon as possible.
271 void setContextSwitches(void);
272 INLINE_HEADER void contextSwitchCapability(Capability *cap);
274 // Free all capabilities
275 void freeCapabilities (void);
278 void markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
279 rtsBool no_mark_sparks);
280 void markCapabilities (evac_fn evac, void *user);
281 void traverseSparkQueues (evac_fn evac, void *user);
283 /* -----------------------------------------------------------------------------
285 -------------------------------------------------------------------------- */
289 INLINE_HEADER rtsBool emptyInbox(Capability *cap);;
291 #endif // THREADED_RTS
293 /* -----------------------------------------------------------------------------
294 * INLINE functions... private below here
295 * -------------------------------------------------------------------------- */
298 recordMutableCap (StgClosure *p, Capability *cap, nat gen)
302 // We must own this Capability in order to modify its mutable list.
303 // ASSERT(cap->running_task == myTask());
304 // NO: assertion is violated by performPendingThrowTos()
305 bd = cap->mut_lists[gen];
306 if (bd->free >= bd->start + BLOCK_SIZE_W) {
308 new_bd = allocBlock_lock();
311 cap->mut_lists[gen] = bd;
313 *bd->free++ = (StgWord)p;
317 recordClosureMutated (Capability *cap, StgClosure *p)
320 bd = Bdescr((StgPtr)p);
321 if (bd->gen_no != 0) recordMutableCap(p,cap,bd->gen_no);
325 #if defined(THREADED_RTS)
326 INLINE_HEADER rtsBool
327 emptySparkPoolCap (Capability *cap)
328 { return looksEmpty(cap->sparks); }
331 sparkPoolSizeCap (Capability *cap)
332 { return sparkPoolSize(cap->sparks); }
335 discardSparksCap (Capability *cap)
336 { return discardSparks(cap->sparks); }
340 contextSwitchCapability (Capability *cap)
342 // setting HpLim to NULL ensures that the next heap check will
343 // fail, and the thread will return to the scheduler.
344 cap->r.rHpLim = NULL;
345 // But just in case it didn't work (the target thread might be
346 // modifying HpLim at the same time), we set the end-of-block
347 // context-switch flag too:
348 cap->context_switch = 1;
353 INLINE_HEADER rtsBool emptyInbox(Capability *cap)
355 return (cap->inbox == (Message*)END_TSO_QUEUE);
360 #include "EndPrivate.h"
362 #endif /* CAPABILITY_H */