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      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.
     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 
     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 
     41 SkThreadPool::~SkThreadPool() {
     42     if (kRunning_State == fState) {
     43         this->wait();
     44     }
     45 }
     46 
     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 
     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 
    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