Merge branch 'master' of http://darcs.haskell.org/ghc
[ghc.git] / rts / Task.h
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 2001-2005
4 *
5 * Tasks
6 *
7 * For details on the high-level design, see
8 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Scheduler
9 *
10 * -------------------------------------------------------------------------*/
11
12 #ifndef TASK_H
13 #define TASK_H
14
15 #include "GetTime.h"
16
17 #include "BeginPrivate.h"
18
19 /*
20 Definition of a Task
21 --------------------
22
23 A task is an OSThread that runs Haskell code. Every OSThread that
24 runs inside the RTS, whether as a worker created by the RTS or via
25 an in-call from C to Haskell, has an associated Task. The first
26 time an OS thread calls into Haskell it is allocated a Task, which
27 remains until the RTS is shut down.
28
29 There is a one-to-one relationship between OSThreads and Tasks.
30 The Task for an OSThread is kept in thread-local storage, and can
31 be retrieved at any time using myTask().
32
33 In the THREADED_RTS build, multiple Tasks may all be running
34 Haskell code simultaneously. A task relinquishes its Capability
35 when it is asked to evaluate an external (C) call.
36
37 Ownership of Task
38 -----------------
39
40 The OS thread named in the Task structure has exclusive access to
41 the structure, as long as it is the running_task of its Capability.
42 That is, if (task->cap->running_task == task), then task->id owns
43 the Task. Otherwise the Task is owned by the owner of the parent
44 data structure on which it is sleeping; for example, if the task is
45 sleeping on spare_workers field of a Capability, then the owner of the
46 Capability has access to the Task.
47
48 When a task is migrated from sleeping on one Capability to another,
49 its task->cap field must be modified. When the task wakes up, it
50 will read the new value of task->cap to find out which Capability
51 it belongs to. Hence some synchronisation is required on
52 task->cap, and this is why we have task->lock.
53
54 If the Task is not currently owned by task->id, then the thread is
55 either
56
57 (a) waiting on the condition task->cond. The Task is either
58 (1) a bound Task, the TSO will be on a queue somewhere
59 (2) a worker task, on the spare_workers queue of task->cap.
60
61 (b) making a foreign call. The InCall will be on the
62 suspended_ccalls list.
63
64 We re-establish ownership in each case by respectively
65
66 (a) the task is currently blocked in yieldCapability().
67 This call will return when we have ownership of the Task and
68 a Capability. The Capability we get might not be the same
69 as the one we had when we called yieldCapability().
70
71 (b) we must call resumeThread(task), which will safely establish
72 ownership of the Task and a Capability.
73 */
74
75 // The InCall structure represents either a single in-call from C to
76 // Haskell, or a worker thread.
77 typedef struct InCall_ {
78 StgTSO * tso; // the bound TSO (or NULL for a worker)
79
80 StgTSO * suspended_tso; // the TSO is stashed here when we
81 // make a foreign call (NULL otherwise);
82
83 Capability *suspended_cap; // The capability that the
84 // suspended_tso is on, because
85 // we can't read this from the TSO
86 // without owning a Capability in the
87 // first place.
88
89 SchedulerStatus stat; // return status
90 StgClosure ** ret; // return value
91
92 struct Task_ *task;
93
94 // When a Haskell thread makes a foreign call that re-enters
95 // Haskell, we end up with another Task associated with the
96 // current thread. We have to remember the whole stack of InCalls
97 // associated with the current Task so that we can correctly
98 // save & restore the InCall on entry to and exit from Haskell.
99 struct InCall_ *prev_stack;
100
101 // Links InCalls onto suspended_ccalls, spare_incalls
102 struct InCall_ *prev;
103 struct InCall_ *next;
104 } InCall;
105
106 typedef struct Task_ {
107 #if defined(THREADED_RTS)
108 OSThreadId id; // The OS Thread ID of this task
109
110 Condition cond; // used for sleeping & waking up this task
111 Mutex lock; // lock for the condition variable
112
113 // this flag tells the task whether it should wait on task->cond
114 // or just continue immediately. It's a workaround for the fact
115 // that signalling a condition variable doesn't do anything if the
116 // thread is already running, but we want it to be sticky.
117 rtsBool wakeup;
118 #endif
119
120 // This points to the Capability that the Task "belongs" to. If
121 // the Task owns a Capability, then task->cap points to it. If
122 // the task does not own a Capability, then either (a) if the task
123 // is a worker, then task->cap points to the Capability it belongs
124 // to, or (b) it is returning from a foreign call, then task->cap
125 // points to the Capability with the returning_worker queue that this
126 // this Task is on.
127 //
128 // When a task goes to sleep, it may be migrated to a different
129 // Capability. Hence, we always check task->cap on wakeup. To
130 // syncrhonise between the migrater and the migratee, task->lock
131 // must be held when modifying task->cap.
132 struct Capability_ *cap;
133
134 // The current top-of-stack InCall
135 struct InCall_ *incall;
136
137 nat n_spare_incalls;
138 struct InCall_ *spare_incalls;
139
140 rtsBool worker; // == rtsTrue if this is a worker Task
141 rtsBool stopped; // this task has stopped or exited Haskell
142
143 // So that we can detect when a finalizer illegally calls back into Haskell
144 rtsBool running_finalizers;
145
146 // Stats that we collect about this task
147 // ToDo: we probably want to put this in a separate TaskStats
148 // structure, so we can share it between multiple Tasks. We don't
149 // really want separate stats for each call in a nested chain of
150 // foreign->haskell->foreign->haskell calls, but we'll get a
151 // separate Task for each of the haskell calls.
152 Time elapsedtimestart;
153 Time muttimestart;
154 Time mut_time;
155 Time mut_etime;
156 Time gc_time;
157 Time gc_etime;
158
159 // Links tasks on the returning_tasks queue of a Capability, and
160 // on spare_workers.
161 struct Task_ *next;
162
163 // Links tasks on the all_tasks list
164 struct Task_ *all_link;
165
166 } Task;
167
168 INLINE_HEADER rtsBool
169 isBoundTask (Task *task)
170 {
171 return (task->incall->tso != NULL);
172 }
173
174
175 // Linked list of all tasks.
176 //
177 extern Task *all_tasks;
178
179 // Start and stop the task manager.
180 // Requires: sched_mutex.
181 //
182 void initTaskManager (void);
183 nat freeTaskManager (void);
184
185 // Create a new Task for a bound thread
186 // Requires: sched_mutex.
187 //
188 Task *newBoundTask (void);
189
190 // The current task is a bound task that is exiting.
191 // Requires: sched_mutex.
192 //
193 void boundTaskExiting (Task *task);
194
195 // Notify the task manager that a task has stopped. This is used
196 // mainly for stats-gathering purposes.
197 // Requires: sched_mutex.
198 //
199 #if defined(THREADED_RTS)
200 // In the non-threaded RTS, tasks never stop.
201 void workerTaskStop (Task *task);
202 #endif
203
204 // Record the time spent in this Task.
205 // This is called by workerTaskStop() but not by boundTaskExiting(),
206 // because it would impose an extra overhead on call-in.
207 //
208 void taskTimeStamp (Task *task);
209
210 // The current Task has finished a GC, record the amount of time spent.
211 void taskDoneGC (Task *task, Time cpu_time, Time elapsed_time);
212
213 // Put the task back on the free list, mark it stopped. Used by
214 // forkProcess().
215 //
216 void discardTasksExcept (Task *keep);
217
218 // Get the Task associated with the current OS thread (or NULL if none).
219 //
220 INLINE_HEADER Task *myTask (void);
221
222 #if defined(THREADED_RTS)
223
224 // Workers are attached to the supplied Capability. This Capability
225 // should not currently have a running_task, because the new task
226 // will become the running_task for that Capability.
227 // Requires: sched_mutex.
228 //
229 void startWorkerTask (Capability *cap);
230
231 // Interrupts a worker task that is performing an FFI call. The thread
232 // should not be destroyed.
233 //
234 void interruptWorkerTask (Task *task);
235
236 #endif /* THREADED_RTS */
237
238 // -----------------------------------------------------------------------------
239 // INLINE functions... private from here on down:
240
241 // A thread-local-storage key that we can use to get access to the
242 // current thread's Task structure.
243 #if defined(THREADED_RTS)
244 #if ((defined(linux_HOST_OS) && \
245 (defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH))) || \
246 (defined(mingw32_HOST_OS) && __GNUC__ >= 4 && __GNUC_MINOR__ >= 4)) && \
247 (!defined(llvm_CC_FLAVOR))
248 #define MYTASK_USE_TLV
249 extern __thread Task *my_task;
250 #else
251 extern ThreadLocalKey currentTaskKey;
252 #endif
253 // LLVM-based compilers do not upport the __thread attribute, so we need
254 // to store the gct variable as a pthread local storage. We declare the
255 // key here to keep thread local storage initialization in the same place.
256 #if defined(llvm_CC_FLAVOR)
257 extern ThreadLocalKey gctKey;
258 #endif
259 #else
260 extern Task *my_task;
261 #endif
262
263 //
264 // myTask() uses thread-local storage to find the Task associated with
265 // the current OS thread. If the current OS thread has multiple
266 // Tasks, because it has re-entered the RTS, then the task->prev_stack
267 // field is used to store the previous Task.
268 //
269 INLINE_HEADER Task *
270 myTask (void)
271 {
272 #if defined(THREADED_RTS) && !defined(MYTASK_USE_TLV)
273 return getThreadLocalVar(&currentTaskKey);
274 #else
275 return my_task;
276 #endif
277 }
278
279 INLINE_HEADER void
280 setMyTask (Task *task)
281 {
282 #if defined(THREADED_RTS) && !defined(MYTASK_USE_TLV)
283 setThreadLocalVar(&currentTaskKey,task);
284 #else
285 my_task = task;
286 #endif
287 }
288
289 #include "EndPrivate.h"
290
291 #endif /* TASK_H */