rts: enable parallel GC scan of large (32M+) allocation area
[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://ghc.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 Task ownership is a little tricky. The default situation is that
41 the Task is an OS-thread-local structure that is owned by the OS
42 thread named in task->id. An OS thread not currently executing
43 Haskell code might call newBoundTask() at any time, which assumes
44 that it has access to the Task for the current OS thread.
45
46 The all_next and all_prev fields of a Task are owned by
47 all_tasks_mutex, which must also be taken if we want to create or
48 free a Task.
49
50 For an OS thread in Haskell, if (task->cap->running_task != task),
51 then the Task is owned by the owner of the parent data structure on
52 which it is sleeping; for example, if the task is sleeping on
53 spare_workers field of a Capability, then the owner of the
54 Capability has access to the Task.
55
56 When a task is migrated from sleeping on one Capability to another,
57 its task->cap field must be modified. When the task wakes up, it
58 will read the new value of task->cap to find out which Capability
59 it belongs to. Hence some synchronisation is required on
60 task->cap, and this is why we have task->lock.
61
62 If the Task is not currently owned by task->id, then the thread is
63 either
64
65 (a) waiting on the condition task->cond. The Task is either
66 (1) a bound Task, the TSO will be on a queue somewhere
67 (2) a worker task, on the spare_workers queue of task->cap.
68
69 (b) making a foreign call. The InCall will be on the
70 suspended_ccalls list.
71
72 We re-establish ownership in each case by respectively
73
74 (a) the task is currently blocked in yieldCapability().
75 This call will return when we have ownership of the Task and
76 a Capability. The Capability we get might not be the same
77 as the one we had when we called yieldCapability().
78
79 (b) we must call resumeThread(task), which will safely establish
80 ownership of the Task and a Capability.
81 */
82
83 // The InCall structure represents either a single in-call from C to
84 // Haskell, or a worker thread.
85 typedef struct InCall_ {
86 StgTSO * tso; // the bound TSO (or NULL for a worker)
87
88 StgTSO * suspended_tso; // the TSO is stashed here when we
89 // make a foreign call (NULL otherwise);
90
91 Capability *suspended_cap; // The capability that the
92 // suspended_tso is on, because
93 // we can't read this from the TSO
94 // without owning a Capability in the
95 // first place.
96
97 SchedulerStatus rstat; // return status
98 StgClosure ** ret; // return value
99
100 struct Task_ *task;
101
102 // When a Haskell thread makes a foreign call that re-enters
103 // Haskell, we end up with another Task associated with the
104 // current thread. We have to remember the whole stack of InCalls
105 // associated with the current Task so that we can correctly
106 // save & restore the InCall on entry to and exit from Haskell.
107 struct InCall_ *prev_stack;
108
109 // Links InCalls onto suspended_ccalls, spare_incalls
110 struct InCall_ *prev;
111 struct InCall_ *next;
112 } InCall;
113
114 typedef struct Task_ {
115 #if defined(THREADED_RTS)
116 OSThreadId id; // The OS Thread ID of this task
117
118 // The NUMA node this Task belongs to. If this is a worker thread, then the
119 // OS thread will be bound to this node (see workerStart()). If this is an
120 // external thread calling into Haskell, it can be bound to a node using
121 // rts_setInCallCapability().
122 uint32_t node;
123
124 Condition cond; // used for sleeping & waking up this task
125 Mutex lock; // lock for the condition variable
126
127 // this flag tells the task whether it should wait on task->cond
128 // or just continue immediately. It's a workaround for the fact
129 // that signalling a condition variable doesn't do anything if the
130 // thread is already running, but we want it to be sticky.
131 rtsBool wakeup;
132 #endif
133
134 // If the task owns a Capability, task->cap points to it. (occasionally a
135 // task may own multiple capabilities, in which case task->cap may point to
136 // any of them. We must be careful to set task->cap to the appropriate one
137 // when using Capability APIs.)
138 //
139 // If the task is a worker, task->cap points to the Capability on which it
140 // is queued.
141 //
142 // If the task is in an unsafe foreign call, then task->cap can be used to
143 // retrieve the capability (see rts_unsafeGetMyCapability()).
144 struct Capability_ *cap;
145
146 // The current top-of-stack InCall
147 struct InCall_ *incall;
148
149 uint32_t n_spare_incalls;
150 struct InCall_ *spare_incalls;
151
152 rtsBool worker; // == rtsTrue if this is a worker Task
153 rtsBool stopped; // this task has stopped or exited Haskell
154
155 // So that we can detect when a finalizer illegally calls back into Haskell
156 rtsBool running_finalizers;
157
158 // if >= 0, this Capability will be used for in-calls
159 int preferred_capability;
160
161 // Links tasks on the returning_tasks queue of a Capability, and
162 // on spare_workers.
163 struct Task_ *next;
164
165 // Links tasks on the all_tasks list; need ACQUIRE_LOCK(&all_tasks_mutex)
166 struct Task_ *all_next;
167 struct Task_ *all_prev;
168
169 } Task;
170
171 INLINE_HEADER rtsBool
172 isBoundTask (Task *task)
173 {
174 return (task->incall->tso != NULL);
175 }
176
177 // A Task is currently a worker if
178 // (a) it was created as a worker (task->worker), and
179 // (b) it has not left and re-entered Haskell, in which case
180 // task->incall->prev_stack would be non-NULL.
181 //
182 INLINE_HEADER rtsBool
183 isWorker (Task *task)
184 {
185 return (task->worker && task->incall->prev_stack == NULL);
186 }
187
188 // Linked list of all tasks.
189 //
190 extern Task *all_tasks;
191
192 // The all_tasks list is protected by the all_tasks_mutex
193 #if defined(THREADED_RTS)
194 extern Mutex all_tasks_mutex;
195 #endif
196
197 // Start and stop the task manager.
198 // Requires: sched_mutex.
199 //
200 void initTaskManager (void);
201 uint32_t freeTaskManager (void);
202
203 // Create a new Task for a bound thread. This Task must be released
204 // by calling boundTaskExiting. The Task is cached in
205 // thread-local storage and will remain even after boundTaskExiting()
206 // has been called; to free the memory, see freeMyTask().
207 //
208 Task *newBoundTask (void);
209
210 // The current task is a bound task that is exiting.
211 //
212 void boundTaskExiting (Task *task);
213
214 // Free a Task if one was previously allocated by newBoundTask().
215 // This is not necessary unless the thread that called newBoundTask()
216 // will be exiting, or if this thread has finished calling Haskell
217 // functions.
218 //
219 void freeMyTask(void);
220
221 // Notify the task manager that a task has stopped. This is used
222 // mainly for stats-gathering purposes.
223 // Requires: sched_mutex.
224 //
225 #if defined(THREADED_RTS)
226 // In the non-threaded RTS, tasks never stop.
227 void workerTaskStop (Task *task);
228 #endif
229
230 // Put the task back on the free list, mark it stopped. Used by
231 // forkProcess().
232 //
233 void discardTasksExcept (Task *keep);
234
235 // Get the Task associated with the current OS thread (or NULL if none).
236 //
237 INLINE_HEADER Task *myTask (void);
238
239 #if defined(THREADED_RTS)
240
241 // Workers are attached to the supplied Capability. This Capability
242 // should not currently have a running_task, because the new task
243 // will become the running_task for that Capability.
244 // Requires: sched_mutex.
245 //
246 void startWorkerTask (Capability *cap);
247
248 // Interrupts a worker task that is performing an FFI call. The thread
249 // should not be destroyed.
250 //
251 void interruptWorkerTask (Task *task);
252
253 #endif /* THREADED_RTS */
254
255 // For stats
256 extern uint32_t taskCount;
257 extern uint32_t workerCount;
258 extern uint32_t peakWorkerCount;
259
260 // -----------------------------------------------------------------------------
261 // INLINE functions... private from here on down:
262
263 // A thread-local-storage key that we can use to get access to the
264 // current thread's Task structure.
265 #if defined(THREADED_RTS)
266 #if ((defined(linux_HOST_OS) && \
267 (defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH))) || \
268 (defined(mingw32_HOST_OS) && __GNUC__ >= 4 && __GNUC_MINOR__ >= 4)) && \
269 (!defined(llvm_CC_FLAVOR))
270 #define MYTASK_USE_TLV
271 extern __thread Task *my_task;
272 #else
273 extern ThreadLocalKey currentTaskKey;
274 #endif
275 #else
276 extern Task *my_task;
277 #endif
278
279 //
280 // myTask() uses thread-local storage to find the Task associated with
281 // the current OS thread. If the current OS thread has multiple
282 // Tasks, because it has re-entered the RTS, then the task->prev_stack
283 // field is used to store the previous Task.
284 //
285 INLINE_HEADER Task *
286 myTask (void)
287 {
288 #if defined(THREADED_RTS) && !defined(MYTASK_USE_TLV)
289 return getThreadLocalVar(&currentTaskKey);
290 #else
291 return my_task;
292 #endif
293 }
294
295 INLINE_HEADER void
296 setMyTask (Task *task)
297 {
298 #if defined(THREADED_RTS) && !defined(MYTASK_USE_TLV)
299 setThreadLocalVar(&currentTaskKey,task);
300 #else
301 my_task = task;
302 #endif
303 }
304
305 // Tasks are identified by their OS thread ID, which can be serialised
306 // to StgWord64, as defined below.
307 typedef StgWord64 TaskId;
308
309 // Get a unique serialisable representation for a task id.
310 //
311 // It's only unique within the process. For example if they are emitted in a
312 // log file then it is suitable to work out which log entries are releated.
313 //
314 // This is needed because OSThreadId is an opaque type
315 // and in practice on some platforms it is a pointer type.
316 //
317 #if defined(THREADED_RTS)
318 INLINE_HEADER TaskId serialiseTaskId (OSThreadId taskID) {
319 #if defined(freebsd_HOST_OS) || defined(darwin_HOST_OS)
320 // Here OSThreadId is a pthread_t and pthread_t is a pointer, but within
321 // the process we can still use that pointer value as a unique id.
322 return (TaskId) (size_t) taskID;
323 #else
324 // On Windows, Linux and others it's an integral type to start with.
325 return (TaskId) taskID;
326 #endif
327 }
328 #endif
329
330 //
331 // Get a serialisable Id for the Task's OS thread
332 // Needed mainly for logging since the OSThreadId is an opaque type
333 INLINE_HEADER TaskId
334 serialisableTaskId (Task *task)
335 {
336 #if defined(THREADED_RTS)
337 return serialiseTaskId(task->id);
338 #else
339 return (TaskId) (size_t) task;
340 #endif
341 }
342
343 #include "EndPrivate.h"
344
345 #endif /* TASK_H */