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).
35 StgRegTable r GNU_ATTRIBUTE(packed);
36 // packed eliminates any padding between f and r. Not strictly
37 // necessary, but it means the negative offsets for accessing
38 // the fields of f when we are in STG code are as small as
41 nat no; // capability number.
43 // The Task currently holding this Capability. This task has
44 // exclusive access to the contents of this Capability (apart from
45 // returning_tasks_hd/returning_tasks_tl).
46 // Locks required: cap->lock.
49 // true if this Capability is running Haskell code, used for
50 // catching unsafe call-ins.
53 // true if this Capability is currently in the GC
56 // The run queue. The Task owning this Capability has exclusive
57 // access to its run queue, so can wake up threads without
58 // taking a lock, and the common path through the scheduler is
63 // Tasks currently making safe foreign calls. Doubly-linked.
64 // When returning, a task first acquires the Capability before
65 // removing itself from this list, so that the GC can find all
66 // the suspended TSOs easily. Hence, when migrating a Task from
67 // the returning_tasks list, we must also migrate its entry from
69 Task *suspended_ccalling_tasks;
71 // One mutable list per generation, so we don't need to take any
72 // locks when updating an old-generation thunk. These
73 // mini-mut-lists are moved onto the respective gen->mut_list at
77 // Context switch flag. We used to have one global flag, now one
78 // per capability. Locks required : none (conflicts are harmless)
81 #if defined(THREADED_RTS)
82 // Worker Tasks waiting in the wings. Singly-linked.
85 // This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
88 // Tasks waiting to return from a foreign call, or waiting to make
89 // a new call-in using this Capability (NULL if empty).
90 // NB. this field needs to be modified by tasks other than the
91 // running_task, so it requires cap->lock to modify. A task can
92 // check whether it is NULL without taking the lock, however.
93 Task *returning_tasks_hd; // Singly-linked, with head/tail
94 Task *returning_tasks_tl;
96 // A list of threads to append to this Capability's run queue at
97 // the earliest opportunity. These are threads that have been
98 // woken up by another Capability.
99 StgTSO *wakeup_queue_hd;
100 StgTSO *wakeup_queue_tl;
104 // Stats on spark creation/conversion
106 nat sparks_converted;
110 // Per-capability STM-related data
111 StgTVarWatchQueue *free_tvar_watch_queues;
112 StgInvariantCheckQueue *free_invariant_check_queues;
113 StgTRecChunk *free_trec_chunks;
114 StgTRecHeader *free_trec_headers;
115 nat transaction_tokens;
116 } // typedef Capability is defined in RtsAPI.h
117 // Capabilities are stored in an array, so make sure that adjacent
118 // Capabilities don't share any cache-lines:
119 #ifndef mingw32_HOST_OS
120 ATTRIBUTE_ALIGNED(64)
125 #if defined(THREADED_RTS)
126 #define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
128 #define ASSERT_TASK_ID(task) /*empty*/
131 // These properties should be true when a Task is holding a Capability
132 #define ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task) \
133 ASSERT(cap->running_task != NULL && cap->running_task == task); \
134 ASSERT(task->cap == cap); \
135 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task)
137 // Sometimes a Task holds a Capability, but the Task is not associated
138 // with that Capability (ie. task->cap != cap). This happens when
139 // (a) a Task holds multiple Capabilities, and (b) when the current
140 // Task is bound, its thread has just blocked, and it may have been
141 // moved to another Capability.
142 #define ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task) \
143 ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
144 cap->run_queue_tl == END_TSO_QUEUE : 1); \
145 ASSERT(myTask() == task); \
146 ASSERT_TASK_ID(task);
148 // Converts a *StgRegTable into a *Capability.
150 #define OFFSET(s_type, field) ((size_t)&(((s_type*)0)->field))
152 INLINE_HEADER Capability *
153 regTableToCapability (StgRegTable *reg)
155 return (Capability *)((void *)((unsigned char*)reg - OFFSET(Capability,r)));
158 // Initialise the available capabilities.
160 void initCapabilities (void);
162 // Release a capability. This is called by a Task that is exiting
163 // Haskell to make a foreign call, or in various other cases when we
164 // want to relinquish a Capability that we currently hold.
166 // ASSUMES: cap->running_task is the current Task.
168 #if defined(THREADED_RTS)
169 void releaseCapability (Capability* cap);
170 void releaseAndWakeupCapability (Capability* cap);
171 void releaseCapability_ (Capability* cap, rtsBool always_wakeup);
172 // assumes cap->lock is held
174 // releaseCapability() is empty in non-threaded RTS
175 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
176 INLINE_HEADER void releaseAndWakeupCapability (Capability* cap STG_UNUSED) {};
177 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED,
178 rtsBool always_wakeup STG_UNUSED) {};
182 // one global capability
183 extern Capability MainCapability;
186 // Array of all the capabilities
188 extern nat n_capabilities;
189 extern Capability *capabilities;
191 // The Capability that was last free. Used as a good guess for where
192 // to assign new threads.
194 extern Capability *last_free_capability;
196 // GC indicator, in scope for the scheduler
197 #define PENDING_GC_SEQ 1
198 #define PENDING_GC_PAR 2
199 extern volatile StgWord waiting_for_gc;
201 // Acquires a capability at a return point. If *cap is non-NULL, then
202 // this is taken as a preference for the Capability we wish to
205 // OS threads waiting in this function get priority over those waiting
206 // in waitForCapability().
208 // On return, *cap is non-NULL, and points to the Capability acquired.
210 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
212 INLINE_HEADER void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
214 #if defined(THREADED_RTS)
216 // Gives up the current capability IFF there is a higher-priority
217 // thread waiting for it. This happens in one of two ways:
219 // (a) we are passing the capability to another OS thread, so
220 // that it can run a bound Haskell thread, or
222 // (b) there is an OS thread waiting to return from a foreign call
224 // On return: *pCap is NULL if the capability was released. The
225 // current task should then re-acquire it using waitForCapability().
227 void yieldCapability (Capability** pCap, Task *task);
229 // Acquires a capability for doing some work.
231 // On return: pCap points to the capability.
233 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
235 // Wakes up a thread on a Capability (probably a different Capability
236 // from the one held by the current Task).
238 void wakeupThreadOnCapability (Capability *my_cap, Capability *other_cap,
241 // Wakes up a worker thread on just one Capability, used when we
242 // need to service some global event.
244 void prodOneCapability (void);
245 void prodCapability (Capability *cap, Task *task);
247 // Similar to prodOneCapability(), but prods all of them.
249 void prodAllCapabilities (void);
251 // Waits for a capability to drain of runnable threads and workers,
252 // and then acquires it. Used at shutdown time.
254 void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
256 // Attempt to gain control of a Capability if it is free.
258 rtsBool tryGrabCapability (Capability *cap, Task *task);
260 // Try to find a spark to run
262 StgClosure *findSpark (Capability *cap);
264 // True if any capabilities have sparks
266 rtsBool anySparks (void);
268 INLINE_HEADER rtsBool emptySparkPoolCap (Capability *cap);
269 INLINE_HEADER nat sparkPoolSizeCap (Capability *cap);
270 INLINE_HEADER void discardSparksCap (Capability *cap);
272 #else // !THREADED_RTS
274 // Grab a capability. (Only in the non-threaded RTS; in the threaded
275 // RTS one of the waitFor*Capability() functions must be used).
277 extern void grabCapability (Capability **pCap);
279 #endif /* !THREADED_RTS */
281 // cause all capabilities to context switch as soon as possible.
282 void setContextSwitches(void);
284 // Free all capabilities
285 void freeCapabilities (void);
288 void markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
289 rtsBool prune_sparks);
290 void markCapabilities (evac_fn evac, void *user);
291 void traverseSparkQueues (evac_fn evac, void *user);
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 bd = cap->mut_lists[gen];
305 if (bd->free >= bd->start + BLOCK_SIZE_W) {
307 new_bd = allocBlock_lock();
310 cap->mut_lists[gen] = bd;
312 *bd->free++ = (StgWord)p;
315 #if defined(THREADED_RTS)
316 INLINE_HEADER rtsBool
317 emptySparkPoolCap (Capability *cap)
318 { return looksEmpty(cap->sparks); }
321 sparkPoolSizeCap (Capability *cap)
322 { return sparkPoolSize(cap->sparks); }
325 discardSparksCap (Capability *cap)
326 { return discardSparks(cap->sparks); }
329 #endif /* CAPABILITY_H */