Reorganisation to fix problems related to the gct register variable
[ghc.git] / rts / Capability.h
1 /* ---------------------------------------------------------------------------
2 *
3 * (c) The GHC Team, 2001-2006
4 *
5 * Capabilities
6 *
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
12 * register (BaseReg).
13 *
14 * Only in an THREADED_RTS build will there be multiple capabilities,
15 * in the non-threaded builds there is one global capability, namely
16 * MainCapability.
17 *
18 * This header file contains the functions for working with capabilities.
19 * (the main, and only, consumer of this interface is the scheduler).
20 *
21 * --------------------------------------------------------------------------*/
22
23 #ifndef CAPABILITY_H
24 #define CAPABILITY_H
25
26 #include "RtsFlags.h"
27 #include "Task.h"
28
29 struct Capability_ {
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).
33 StgFunTable f;
34 StgRegTable r;
35
36 nat no; // capability number.
37
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.
42 Task *running_task;
43
44 // true if this Capability is running Haskell code, used for
45 // catching unsafe call-ins.
46 rtsBool in_haskell;
47
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
51 // also lock-free.
52 StgTSO *run_queue_hd;
53 StgTSO *run_queue_tl;
54
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
60 // this list.
61 Task *suspended_ccalling_tasks;
62
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
66 // each GC.
67 bdescr **mut_lists;
68
69 #if defined(THREADED_RTS)
70 // Worker Tasks waiting in the wings. Singly-linked.
71 Task *spare_workers;
72
73 // This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
74 Mutex lock;
75
76 // Tasks waiting to return from a foreign call, or waiting to make
77 // a new call-in using this Capability (NULL if empty).
78 // NB. this field needs to be modified by tasks other than the
79 // running_task, so it requires cap->lock to modify. A task can
80 // check whether it is NULL without taking the lock, however.
81 Task *returning_tasks_hd; // Singly-linked, with head/tail
82 Task *returning_tasks_tl;
83
84 // A list of threads to append to this Capability's run queue at
85 // the earliest opportunity. These are threads that have been
86 // woken up by another Capability.
87 StgTSO *wakeup_queue_hd;
88 StgTSO *wakeup_queue_tl;
89 #endif
90
91 // Per-capability STM-related data
92 StgTVarWatchQueue *free_tvar_watch_queues;
93 StgInvariantCheckQueue *free_invariant_check_queues;
94 StgTRecChunk *free_trec_chunks;
95 StgTRecHeader *free_trec_headers;
96 nat transaction_tokens;
97 }; // typedef Capability, defined in RtsAPI.h
98
99
100 #if defined(THREADED_RTS)
101 #define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
102 #else
103 #define ASSERT_TASK_ID(task) /*empty*/
104 #endif
105
106 // These properties should be true when a Task is holding a Capability
107 #define ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task) \
108 ASSERT(cap->running_task != NULL && cap->running_task == task); \
109 ASSERT(task->cap == cap); \
110 ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task)
111
112 // Sometimes a Task holds a Capability, but the Task is not associated
113 // with that Capability (ie. task->cap != cap). This happens when
114 // (a) a Task holds multiple Capabilities, and (b) when the current
115 // Task is bound, its thread has just blocked, and it may have been
116 // moved to another Capability.
117 #define ASSERT_PARTIAL_CAPABILITY_INVARIANTS(cap,task) \
118 ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
119 cap->run_queue_tl == END_TSO_QUEUE : 1); \
120 ASSERT(myTask() == task); \
121 ASSERT_TASK_ID(task);
122
123 // Converts a *StgRegTable into a *Capability.
124 //
125 INLINE_HEADER Capability *
126 regTableToCapability (StgRegTable *reg)
127 {
128 return (Capability *)((void *)((unsigned char*)reg - sizeof(StgFunTable)));
129 }
130
131 // Initialise the available capabilities.
132 //
133 void initCapabilities (void);
134
135 // Release a capability. This is called by a Task that is exiting
136 // Haskell to make a foreign call, or in various other cases when we
137 // want to relinquish a Capability that we currently hold.
138 //
139 // ASSUMES: cap->running_task is the current Task.
140 //
141 #if defined(THREADED_RTS)
142 void releaseCapability (Capability* cap);
143 void releaseCapability_ (Capability* cap); // assumes cap->lock is held
144 #else
145 // releaseCapability() is empty in non-threaded RTS
146 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
147 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED) {};
148 #endif
149
150 #if !IN_STG_CODE
151 // one global capability
152 extern Capability MainCapability;
153 #endif
154
155 // Array of all the capabilities
156 //
157 extern nat n_capabilities;
158 extern Capability *capabilities;
159
160 // The Capability that was last free. Used as a good guess for where
161 // to assign new threads.
162 //
163 extern Capability *last_free_capability;
164
165 // Acquires a capability at a return point. If *cap is non-NULL, then
166 // this is taken as a preference for the Capability we wish to
167 // acquire.
168 //
169 // OS threads waiting in this function get priority over those waiting
170 // in waitForCapability().
171 //
172 // On return, *cap is non-NULL, and points to the Capability acquired.
173 //
174 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
175
176 INLINE_HEADER void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
177
178 #if defined(THREADED_RTS)
179
180 // Gives up the current capability IFF there is a higher-priority
181 // thread waiting for it. This happens in one of two ways:
182 //
183 // (a) we are passing the capability to another OS thread, so
184 // that it can run a bound Haskell thread, or
185 //
186 // (b) there is an OS thread waiting to return from a foreign call
187 //
188 // On return: *pCap is NULL if the capability was released. The
189 // current task should then re-acquire it using waitForCapability().
190 //
191 void yieldCapability (Capability** pCap, Task *task);
192
193 // Acquires a capability for doing some work.
194 //
195 // On return: pCap points to the capability.
196 //
197 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
198
199 // Wakes up a thread on a Capability (probably a different Capability
200 // from the one held by the current Task).
201 //
202 void wakeupThreadOnCapability (Capability *cap, StgTSO *tso);
203 void wakeupThreadOnCapability_lock (Capability *cap, StgTSO *tso);
204
205 void migrateThreadToCapability (Capability *cap, StgTSO *tso);
206 void migrateThreadToCapability_lock (Capability *cap, StgTSO *tso);
207
208 // Wakes up a worker thread on just one Capability, used when we
209 // need to service some global event.
210 //
211 void prodOneCapability (void);
212
213 // Similar to prodOneCapability(), but prods all of them.
214 //
215 void prodAllCapabilities (void);
216
217 // Waits for a capability to drain of runnable threads and workers,
218 // and then acquires it. Used at shutdown time.
219 //
220 void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
221
222 // Attempt to gain control of a Capability if it is free.
223 //
224 rtsBool tryGrabCapability (Capability *cap, Task *task);
225
226 #else // !THREADED_RTS
227
228 // Grab a capability. (Only in the non-threaded RTS; in the threaded
229 // RTS one of the waitFor*Capability() functions must be used).
230 //
231 extern void grabCapability (Capability **pCap);
232
233 #endif /* !THREADED_RTS */
234
235 // Free a capability on exit
236 void freeCapability (Capability *cap);
237
238 // FOr the GC:
239 void markSomeCapabilities (evac_fn evac, void *user, nat i0, nat delta);
240 void markCapabilities (evac_fn evac, void *user);
241
242 /* -----------------------------------------------------------------------------
243 * INLINE functions... private below here
244 * -------------------------------------------------------------------------- */
245
246 INLINE_HEADER void
247 recordMutableCap (StgClosure *p, Capability *cap, nat gen)
248 {
249 bdescr *bd;
250
251 bd = cap->mut_lists[gen];
252 if (bd->free >= bd->start + BLOCK_SIZE_W) {
253 bdescr *new_bd;
254 new_bd = allocBlock_lock();
255 new_bd->link = bd;
256 bd = new_bd;
257 cap->mut_lists[gen] = bd;
258 }
259 *bd->free++ = (StgWord)p;
260 }
261
262 #endif /* CAPABILITY_H */