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 // 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 Task *suspended_ccalling_tasks;
64 // One mutable list per generation, so we don't need to take any
65 // locks when updating an old-generation thunk. These
66 // mini-mut-lists are moved onto the respective gen->mut_list at
70 // Context switch flag. We used to have one global flag, now one
71 // per capability. Locks required : none (conflicts are harmless)
74 #if defined(THREADED_RTS)
75 // Worker Tasks waiting in the wings. Singly-linked.
78 // This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
81 // Tasks waiting to return from a foreign call, or waiting to make
82 // a new call-in using this Capability (NULL if empty).
83 // NB. this field needs to be modified by tasks other than the
84 // running_task, so it requires cap->lock to modify. A task can
85 // check whether it is NULL without taking the lock, however.
86 Task *returning_tasks_hd; // Singly-linked, with head/tail
87 Task *returning_tasks_tl;
89 // A list of threads to append to this Capability's run queue at
90 // the earliest opportunity. These are threads that have been
91 // woken up by another Capability.
92 StgTSO *wakeup_queue_hd;
93 StgTSO *wakeup_queue_tl;
97 // Stats on spark creation/conversion
103 // Per-capability STM-related data
104 StgTVarWatchQueue *free_tvar_watch_queues;
105 StgInvariantCheckQueue *free_invariant_check_queues;
106 StgTRecChunk *free_trec_chunks;
107 StgTRecHeader *free_trec_headers;
108 nat transaction_tokens;
109 } // typedef Capability is defined in RtsAPI.h
110 // Capabilities are stored in an array, so make sure that adjacent
111 // Capabilities don't share any cache-lines:
112 ATTRIBUTE_ALIGNED(64);
115 #if defined(THREADED_RTS)
116 #define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
118 #define ASSERT_TASK_ID(task) /*empty*/
121 // These properties should be true when a Task is holding a Capability
122 #define ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task) \
123 ASSERT(cap->running_task != NULL && cap->running_task == task); \
124 ASSERT(task->cap == cap); \
125 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task)
127 // Sometimes a Task holds a Capability, but the Task is not associated
128 // with that Capability (ie. task->cap != cap). This happens when
129 // (a) a Task holds multiple Capabilities, and (b) when the current
130 // Task is bound, its thread has just blocked, and it may have been
131 // moved to another Capability.
132 #define ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task) \
133 ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
134 cap->run_queue_tl == END_TSO_QUEUE : 1); \
135 ASSERT(myTask() == task); \
136 ASSERT_TASK_ID(task);
138 // Converts a *StgRegTable into a *Capability.
140 INLINE_HEADER Capability *
141 regTableToCapability (StgRegTable *reg)
143 return (Capability *)((void *)((unsigned char*)reg - sizeof(StgFunTable)));
146 // Initialise the available capabilities.
148 void initCapabilities (void);
150 // Release a capability. This is called by a Task that is exiting
151 // Haskell to make a foreign call, or in various other cases when we
152 // want to relinquish a Capability that we currently hold.
154 // ASSUMES: cap->running_task is the current Task.
156 #if defined(THREADED_RTS)
157 void releaseCapability (Capability* cap);
158 void releaseAndWakeupCapability (Capability* cap);
159 void releaseCapability_ (Capability* cap, rtsBool always_wakeup);
160 // assumes cap->lock is held
162 // releaseCapability() is empty in non-threaded RTS
163 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
164 INLINE_HEADER void releaseAndWakeupCapability (Capability* cap STG_UNUSED) {};
165 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED,
166 rtsBool always_wakeup STG_UNUSED) {};
170 // one global capability
171 extern Capability MainCapability;
174 // Array of all the capabilities
176 extern nat n_capabilities;
177 extern Capability *capabilities;
179 // The Capability that was last free. Used as a good guess for where
180 // to assign new threads.
182 extern Capability *last_free_capability;
184 // GC indicator, in scope for the scheduler
185 extern volatile StgWord waiting_for_gc;
187 // Acquires a capability at a return point. If *cap is non-NULL, then
188 // this is taken as a preference for the Capability we wish to
191 // OS threads waiting in this function get priority over those waiting
192 // in waitForCapability().
194 // On return, *cap is non-NULL, and points to the Capability acquired.
196 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
198 INLINE_HEADER void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
200 #if defined(THREADED_RTS)
202 // Gives up the current capability IFF there is a higher-priority
203 // thread waiting for it. This happens in one of two ways:
205 // (a) we are passing the capability to another OS thread, so
206 // that it can run a bound Haskell thread, or
208 // (b) there is an OS thread waiting to return from a foreign call
210 // On return: *pCap is NULL if the capability was released. The
211 // current task should then re-acquire it using waitForCapability().
213 void yieldCapability (Capability** pCap, Task *task);
215 // Acquires a capability for doing some work.
217 // On return: pCap points to the capability.
219 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
221 // Wakes up a thread on a Capability (probably a different Capability
222 // from the one held by the current Task).
224 void wakeupThreadOnCapability (Capability *my_cap, Capability *other_cap,
227 // Wakes up a worker thread on just one Capability, used when we
228 // need to service some global event.
230 void prodOneCapability (void);
232 // Similar to prodOneCapability(), but prods all of them.
234 void prodAllCapabilities (void);
236 // Waits for a capability to drain of runnable threads and workers,
237 // and then acquires it. Used at shutdown time.
239 void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
241 // Attempt to gain control of a Capability if it is free.
243 rtsBool tryGrabCapability (Capability *cap, Task *task);
245 // Try to steal a spark from other Capabilities
247 StgClosure *stealWork (Capability *cap);
249 // True if any capabilities have sparks
251 rtsBool anySparks (void);
253 INLINE_HEADER rtsBool emptySparkPoolCap (Capability *cap);
254 INLINE_HEADER nat sparkPoolSizeCap (Capability *cap);
255 INLINE_HEADER void discardSparksCap (Capability *cap);
257 #else // !THREADED_RTS
259 // Grab a capability. (Only in the non-threaded RTS; in the threaded
260 // RTS one of the waitFor*Capability() functions must be used).
262 extern void grabCapability (Capability **pCap);
264 #endif /* !THREADED_RTS */
266 // cause all capabilities to context switch as soon as possible.
267 void setContextSwitches(void);
269 // Free all capabilities
270 void freeCapabilities (void);
273 void markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta,
274 rtsBool prune_sparks);
275 void markCapabilities (evac_fn evac, void *user);
276 void traverseSparkQueues (evac_fn evac, void *user);
278 /* -----------------------------------------------------------------------------
279 * INLINE functions... private below here
280 * -------------------------------------------------------------------------- */
283 recordMutableCap (StgClosure *p, Capability *cap, nat gen)
287 // We must own this Capability in order to modify its mutable list.
288 ASSERT(cap->running_task == myTask());
289 bd = cap->mut_lists[gen];
290 if (bd->free >= bd->start + BLOCK_SIZE_W) {
292 new_bd = allocBlock_lock();
295 cap->mut_lists[gen] = bd;
297 *bd->free++ = (StgWord)p;
300 #if defined(THREADED_RTS)
301 INLINE_HEADER rtsBool
302 emptySparkPoolCap (Capability *cap)
303 { return looksEmpty(cap->sparks); }
306 sparkPoolSizeCap (Capability *cap)
307 { return sparkPoolSize(cap->sparks); }
310 discardSparksCap (Capability *cap)
311 { return discardSparks(cap->sparks); }
314 #endif /* CAPABILITY_H */