1 /*
2 * Copyright 2012 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #include "SkRunnable.h"
9 #include "SkThreadPool.h"
10 #include "SkThreadUtils.h"
11 #include "SkTypes.h"
12
13 #if defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_ANDROID)
14 #include <unistd.h>
15 #endif
16
17 // Returns the number of cores on this machine.
num_cores()18 static int num_cores() {
19 #if defined(SK_BUILD_FOR_WIN32)
20 SYSTEM_INFO sysinfo;
21 GetSystemInfo(&sysinfo);
22 return sysinfo.dwNumberOfProcessors;
23 #elif defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_ANDROID)
24 return sysconf(_SC_NPROCESSORS_ONLN);
25 #else
26 return 1;
27 #endif
28 }
29
SkThreadPool(int count)30 SkThreadPool::SkThreadPool(int count)
31 : fState(kRunning_State), fBusyThreads(0) {
32 if (count < 0) count = num_cores();
33 // Create count threads, all running SkThreadPool::Loop.
34 for (int i = 0; i < count; i++) {
35 SkThread* thread = SkNEW_ARGS(SkThread, (&SkThreadPool::Loop, this));
36 *fThreads.append() = thread;
37 thread->start();
38 }
39 }
40
~SkThreadPool()41 SkThreadPool::~SkThreadPool() {
42 if (kRunning_State == fState) {
43 this->wait();
44 }
45 }
46
wait()47 void SkThreadPool::wait() {
48 fReady.lock();
49 fState = kWaiting_State;
50 fReady.broadcast();
51 fReady.unlock();
52
53 // Wait for all threads to stop.
54 for (int i = 0; i < fThreads.count(); i++) {
55 fThreads[i]->join();
56 SkDELETE(fThreads[i]);
57 }
58 SkASSERT(fQueue.isEmpty());
59 }
60
Loop(void * arg)61 /*static*/ void SkThreadPool::Loop(void* arg) {
62 // The SkThreadPool passes itself as arg to each thread as they're created.
63 SkThreadPool* pool = static_cast<SkThreadPool*>(arg);
64
65 while (true) {
66 // We have to be holding the lock to read the queue and to call wait.
67 pool->fReady.lock();
68 while(pool->fQueue.isEmpty()) {
69 // Does the client want to stop and are all the threads ready to stop?
70 // If so, we move into the halting state, and whack all the threads so they notice.
71 if (kWaiting_State == pool->fState && pool->fBusyThreads == 0) {
72 pool->fState = kHalting_State;
73 pool->fReady.broadcast();
74 }
75 // Any time we find ourselves in the halting state, it's quitting time.
76 if (kHalting_State == pool->fState) {
77 pool->fReady.unlock();
78 return;
79 }
80 // wait yields the lock while waiting, but will have it again when awoken.
81 pool->fReady.wait();
82 }
83 // We've got the lock back here, no matter if we ran wait or not.
84
85 // The queue is not empty, so we have something to run. Claim it.
86 LinkedRunnable* r = pool->fQueue.tail();
87
88 pool->fQueue.remove(r);
89
90 // Having claimed our SkRunnable, we now give up the lock while we run it.
91 // Otherwise, we'd only ever do work on one thread at a time, which rather
92 // defeats the point of this code.
93 pool->fBusyThreads++;
94 pool->fReady.unlock();
95
96 // OK, now really do the work.
97 r->fRunnable->run();
98 SkDELETE(r);
99
100 // Let everyone know we're not busy.
101 pool->fReady.lock();
102 pool->fBusyThreads--;
103 pool->fReady.unlock();
104 }
105
106 SkASSERT(false); // Unreachable. The only exit happens when pool->fState is kHalting_State.
107 }
108
add(SkRunnable * r)109 void SkThreadPool::add(SkRunnable* r) {
110 if (NULL == r) {
111 return;
112 }
113
114 // If we don't have any threads, obligingly just run the thing now.
115 if (fThreads.isEmpty()) {
116 return r->run();
117 }
118
119 // We have some threads. Queue it up!
120 fReady.lock();
121 SkASSERT(fState != kHalting_State); // Shouldn't be able to add work when we're halting.
122 LinkedRunnable* linkedRunnable = SkNEW(LinkedRunnable);
123 linkedRunnable->fRunnable = r;
124 fQueue.addToHead(linkedRunnable);
125 fReady.signal();
126 fReady.unlock();
127 }
128