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 * --------------------------------------------------------------------------*/
30 // State required by the STG virtual machine when running Haskell
31 // code. During STG execution, the BaseReg register always points
32 // to the StgRegTable of the current Capability (&cap->r).
36 nat no; // capability number.
38 // The Task currently holding this Capability. This task has
39 // exclusive access to the contents of this Capability (apart from
40 // returning_tasks_hd/returning_tasks_tl).
41 // Locks required: cap->lock.
44 // true if this Capability is running Haskell code, used for
45 // catching unsafe call-ins.
48 // The run queue. The Task owning this Capability has exclusive
49 // access to its run queue, so can wake up threads without
50 // taking a lock, and the common path through the scheduler is
55 // Tasks currently making safe foreign calls. Doubly-linked.
56 // When returning, a task first acquires the Capability before
57 // removing itself from this list, so that the GC can find all
58 // the suspended TSOs easily. Hence, when migrating a Task from
59 // the returning_tasks list, we must also migrate its entry from
61 Task *suspended_ccalling_tasks;
63 // One mutable list per generation, so we don't need to take any
64 // locks when updating an old-generation thunk. These
65 // mini-mut-lists are moved onto the respective gen->mut_list at
69 // Context switch flag. We used to have one global flag, now one
70 // per capability. Locks required : none (conflicts are harmless)
73 #if defined(THREADED_RTS)
74 // Worker Tasks waiting in the wings. Singly-linked.
77 // This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
80 // Tasks waiting to return from a foreign call, or waiting to make
81 // a new call-in using this Capability (NULL if empty).
82 // NB. this field needs to be modified by tasks other than the
83 // running_task, so it requires cap->lock to modify. A task can
84 // check whether it is NULL without taking the lock, however.
85 Task *returning_tasks_hd; // Singly-linked, with head/tail
86 Task *returning_tasks_tl;
88 // A list of threads to append to this Capability's run queue at
89 // the earliest opportunity. These are threads that have been
90 // woken up by another Capability.
91 StgTSO *wakeup_queue_hd;
92 StgTSO *wakeup_queue_tl;
95 // Per-capability STM-related data
96 StgTVarWatchQueue *free_tvar_watch_queues;
97 StgInvariantCheckQueue *free_invariant_check_queues;
98 StgTRecChunk *free_trec_chunks;
99 StgTRecHeader *free_trec_headers;
100 nat transaction_tokens;
101 }; // typedef Capability, defined in RtsAPI.h
104 #if defined(THREADED_RTS)
105 #define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
107 #define ASSERT_TASK_ID(task) /*empty*/
110 // These properties should be true when a Task is holding a Capability
111 #define ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task) \
112 ASSERT(cap->running_task != NULL && cap->running_task == task); \
113 ASSERT(task->cap == cap); \
114 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task)
116 // Sometimes a Task holds a Capability, but the Task is not associated
117 // with that Capability (ie. task->cap != cap). This happens when
118 // (a) a Task holds multiple Capabilities, and (b) when the current
119 // Task is bound, its thread has just blocked, and it may have been
120 // moved to another Capability.
121 #define ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task) \
122 ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
123 cap->run_queue_tl == END_TSO_QUEUE : 1); \
124 ASSERT(myTask() == task); \
125 ASSERT_TASK_ID(task);
127 // Converts a *StgRegTable into a *Capability.
129 INLINE_HEADER Capability *
130 regTableToCapability (StgRegTable *reg)
132 return (Capability *)((void *)((unsigned char*)reg - sizeof(StgFunTable)));
135 // Initialise the available capabilities.
137 void initCapabilities (void);
139 // Release a capability. This is called by a Task that is exiting
140 // Haskell to make a foreign call, or in various other cases when we
141 // want to relinquish a Capability that we currently hold.
143 // ASSUMES: cap->running_task is the current Task.
145 #if defined(THREADED_RTS)
146 void releaseCapability (Capability* cap);
147 void releaseCapability_ (Capability* cap); // assumes cap->lock is held
149 // releaseCapability() is empty in non-threaded RTS
150 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
151 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED) {};
155 // one global capability
156 extern Capability MainCapability;
159 // Array of all the capabilities
161 extern nat n_capabilities;
162 extern Capability *capabilities;
164 // The Capability that was last free. Used as a good guess for where
165 // to assign new threads.
167 extern Capability *last_free_capability;
169 // GC indicator, in scope for the scheduler
170 extern volatile StgWord waiting_for_gc;
172 // Acquires a capability at a return point. If *cap is non-NULL, then
173 // this is taken as a preference for the Capability we wish to
176 // OS threads waiting in this function get priority over those waiting
177 // in waitForCapability().
179 // On return, *cap is non-NULL, and points to the Capability acquired.
181 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
183 INLINE_HEADER void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
185 #if defined(THREADED_RTS)
187 // Gives up the current capability IFF there is a higher-priority
188 // thread waiting for it. This happens in one of two ways:
190 // (a) we are passing the capability to another OS thread, so
191 // that it can run a bound Haskell thread, or
193 // (b) there is an OS thread waiting to return from a foreign call
195 // On return: *pCap is NULL if the capability was released. The
196 // current task should then re-acquire it using waitForCapability().
198 void yieldCapability (Capability** pCap, Task *task);
200 // Acquires a capability for doing some work.
202 // On return: pCap points to the capability.
204 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
206 // Wakes up a thread on a Capability (probably a different Capability
207 // from the one held by the current Task).
209 void wakeupThreadOnCapability (Capability *my_cap, Capability *other_cap,
212 // Wakes up a worker thread on just one Capability, used when we
213 // need to service some global event.
215 void prodOneCapability (void);
217 // Similar to prodOneCapability(), but prods all of them.
219 void prodAllCapabilities (void);
221 // Waits for a capability to drain of runnable threads and workers,
222 // and then acquires it. Used at shutdown time.
224 void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
226 // Attempt to gain control of a Capability if it is free.
228 rtsBool tryGrabCapability (Capability *cap, Task *task);
230 #else // !THREADED_RTS
232 // Grab a capability. (Only in the non-threaded RTS; in the threaded
233 // RTS one of the waitFor*Capability() functions must be used).
235 extern void grabCapability (Capability **pCap);
237 #endif /* !THREADED_RTS */
239 // cause all capabilities to context switch as soon as possible.
240 void setContextSwitches(void);
242 // Free a capability on exit
243 void freeCapability (Capability *cap);
246 void markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta);
247 void markCapabilities (evac_fn evac, void *user);
248 void traverseSparkQueues (evac_fn evac, void *user);
250 /* -----------------------------------------------------------------------------
251 * INLINE functions... private below here
252 * -------------------------------------------------------------------------- */
255 recordMutableCap (StgClosure *p, Capability *cap, nat gen)
259 // We must own this Capability in order to modify its mutable list.
260 ASSERT(cap->running_task == myTask());
261 bd = cap->mut_lists[gen];
262 if (bd->free >= bd->start + BLOCK_SIZE_W) {
264 new_bd = allocBlock_lock();
267 cap->mut_lists[gen] = bd;
269 *bd->free++ = (StgWord)p;
272 #endif /* CAPABILITY_H */