netwerk/base/src/nsIOThreadPool.cpp

   1 /* ***** BEGIN LICENSE BLOCK *****
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  14  * The Original Code is Mozilla.
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  16  * The Initial Developer of the Original Code is IBM Corporation.
  17  * Portions created by IBM Corporation are Copyright (C) 2003
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  36
  37 #include "nsIEventTarget.h"
  38 #include "nsIServiceManager.h"
  39 #include "nsIObserverService.h"
  40 #include "nsIObserver.h"
  41 #include "nsAutoLock.h"
  42 #include "nsCOMPtr.h"
  43 #include "prclist.h"
  44 #include "prlog.h"
  45
  46 #if defined(PR_LOGGING)
  47 //
  48 // NSPR_LOG_MODULES=nsIOThreadPool:5
  49 //
  50 static PRLogModuleInfo *gIOThreadPoolLog = nsnull;
  51 #endif
  52 #define LOG(args) PR_LOG(gIOThreadPoolLog, PR_LOG_DEBUG, args)
  53
  54 // this number specifies the maximum number of threads.
  55 #define MAX_THREADS 4
  56
  57 // this number specifies how long to wait before killing an idle thread.  it's
  58 // important to pick a large enough value here to minimize thread churn.
  59 #define IDLE_TIMEOUT PR_SecondsToInterval(60)
  60
  61 #define PLEVENT_FROM_LINK(_link) \
  62     ((PLEvent*) ((char*) (_link) - offsetof(PLEvent, link)))
  63
  64 //-----------------------------------------------------------------------------
  65 // pool of joinable threads used for general purpose i/o tasks
  66 //
  67 // the main entry point to this class is nsIEventTarget.  events posted to
  68 // the thread pool are dispatched on one of the threads.  a variable number
  69 // of threads are maintained.  the threads die off if they remain idle for
  70 // more than THREAD_IDLE_TIMEOUT.  the thread pool shuts down when it receives
  71 // the "xpcom-shutdown-threads" event.
  72 //-----------------------------------------------------------------------------
  73
  74 class nsIOThreadPool : public nsIEventTarget
  75                      , public nsIObserver
  76 {
  77 public:
  78     NS_DECL_ISUPPORTS
  79     NS_DECL_NSIEVENTTARGET
  80     NS_DECL_NSIOBSERVER
  81
  82     nsresult Init();
  83     void     Shutdown();
  84
  85 private:
  86     virtual ~nsIOThreadPool();
  87
  88     static void ThreadFunc(void *);
  89
  90     // mLock protects all (exceptions during Init and Shutdown)
  91     PRLock    *mLock;
  92     PRCondVar *mIdleThreadCV;   // notified to wake up an idle thread
  93     PRCondVar *mExitThreadCV;   // notified when a thread exits
  94     PRUint32   mNumThreads;     // number of active + idle threads
  95     PRUint32   mNumIdleThreads; // number of idle threads
  96     PRCList    mEventQ;         // queue of PLEvent structs
  97     PRBool     mShutdown;       // set to true if shutting down
  98 };
  99
 100 NS_IMPL_THREADSAFE_ISUPPORTS2(nsIOThreadPool, nsIEventTarget, nsIObserver)
 101
 102 nsresult
 103 nsIOThreadPool::Init()
 104 {
 105 #if defined(PR_LOGGING)
 106     if (!gIOThreadPoolLog)
 107         gIOThreadPoolLog = PR_NewLogModule("nsIOThreadPool");
 108 #endif
 109
 110     mNumThreads = 0;
 111     mNumIdleThreads = 0;
 112     mShutdown = PR_FALSE;
 113
 114     mLock = PR_NewLock();
 115     if (!mLock)
 116         return NS_ERROR_OUT_OF_MEMORY;
 117
 118     mIdleThreadCV = PR_NewCondVar(mLock);
 119     if (!mIdleThreadCV)
 120         return NS_ERROR_OUT_OF_MEMORY;
 121
 122     mExitThreadCV = PR_NewCondVar(mLock);
 123     if (!mExitThreadCV)
 124         return NS_ERROR_OUT_OF_MEMORY;
 125
 126     PR_INIT_CLIST(&mEventQ);
 127
 128     // We want to shutdown the i/o thread pool at xpcom-shutdown-threads time.
 129     nsCOMPtr<nsIObserverService> os = do_GetService("@mozilla.org/observer-service;1");
 130     if (os)
 131         os->AddObserver(this, "xpcom-shutdown-threads", PR_FALSE);
 132     return NS_OK;
 133 }
 134
 135 nsIOThreadPool::~nsIOThreadPool()
 136 {
 137     LOG(("Destroying nsIOThreadPool @%p\n", this));
 138
 139 #ifdef DEBUG
 140     NS_ASSERTION(PR_CLIST_IS_EMPTY(&mEventQ), "leaking events");
 141     NS_ASSERTION(mNumThreads == 0, "leaking thread(s)");
 142 #endif
 143
 144     if (mIdleThreadCV)
 145         PR_DestroyCondVar(mIdleThreadCV);
 146     if (mExitThreadCV)
 147         PR_DestroyCondVar(mExitThreadCV);
 148     if (mLock)
 149         PR_DestroyLock(mLock);
 150 }
 151
 152 void
 153 nsIOThreadPool::Shutdown()
 154 {
 155     LOG(("nsIOThreadPool::Shutdown\n"));
 156
 157     // synchronize with background threads...
 158     {
 159         nsAutoLock lock(mLock);
 160         mShutdown = PR_TRUE;
 161
 162         PR_NotifyAllCondVar(mIdleThreadCV);
 163
 164         while (mNumThreads != 0)
 165             PR_WaitCondVar(mExitThreadCV, PR_INTERVAL_NO_TIMEOUT);
 166     }
 167 }
 168
 169 NS_IMETHODIMP
 170 nsIOThreadPool::PostEvent(PLEvent *event)
 171 {
 172     LOG(("nsIOThreadPool::PostEvent [event=%p]\n", event));
 173
 174     nsAutoLock lock(mLock);
 175
 176     // if we are shutting down, then prevent additional events from being
 177     // added to the queue...
 178     if (mShutdown)
 179         return NS_ERROR_UNEXPECTED;
 180
 181     nsresult rv = NS_OK;
 182
 183     PR_APPEND_LINK(&event->link, &mEventQ);
 184
 185     // now, look for an available idle thread...
 186     if (mNumIdleThreads)
 187         PR_NotifyCondVar(mIdleThreadCV); // wake up an idle thread
 188
 189     // or, try to create a new thread unless we have reached our maximum...
 190     else if (mNumThreads < MAX_THREADS) {
 191         NS_ADDREF_THIS(); // the thread owns a reference to us
 192         mNumThreads++;
 193         PRThread *thread = PR_CreateThread(PR_USER_THREAD,
 194                                            ThreadFunc,
 195                                            this,
 196                                            PR_PRIORITY_NORMAL,
 197                                            PR_GLOBAL_THREAD,
 198                                            PR_UNJOINABLE_THREAD,
 199                                            0);
 200         if (!thread) {
 201             NS_RELEASE_THIS();
 202             mNumThreads--;
 203             rv = NS_ERROR_OUT_OF_MEMORY;
 204         }
 205     }
 206     // else, we expect one of the active threads to process the event queue.
 207
 208     return rv;
 209 }
 210
 211 NS_IMETHODIMP
 212 nsIOThreadPool::IsOnCurrentThread(PRBool *result)
 213 {
 214     // no one should be calling this method.  if this assertion gets hit,
 215     // then we need to think carefully about what this method should be
 216     // returning.
 217     NS_NOTREACHED("nsIOThreadPool::IsOnCurrentThread");
 218
 219     // fudging this a bit since we actually cover several threads...
 220     *result = PR_FALSE;
 221     return NS_OK;
 222 }
 223
 224 NS_IMETHODIMP
 225 nsIOThreadPool::Observe(nsISupports *, const char *topic, const PRUnichar *)
 226 {
 227     NS_ASSERTION(strcmp(topic, "xpcom-shutdown-threads") == 0, "unexpected topic");
 228     Shutdown();
 229     return NS_OK;
 230 }
 231
 232 void
 233 nsIOThreadPool::ThreadFunc(void *arg)
 234 {
 235     nsIOThreadPool *pool = (nsIOThreadPool *) arg;
 236
 237     LOG(("entering ThreadFunc\n"));
 238
 239     {
 240         nsAutoLock lock(pool->mLock);
 241
 242         for (;;) {
 243             PRIntervalTime start = PR_IntervalNow(), timeout = IDLE_TIMEOUT;
 244             //
 245             // wait for one or more of the following to occur:
 246             //  (1) the event queue has an event to process
 247             //  (2) the shutdown flag has been set
 248             //  (3) the thread has been idle for too long
 249             //
 250             // PR_WaitCondVar will return when any of these conditions is true.
 251             //
 252             while (PR_CLIST_IS_EMPTY(&pool->mEventQ) && !pool->mShutdown) {
 253                 pool->mNumIdleThreads++;
 254                 PR_WaitCondVar(pool->mIdleThreadCV, timeout);
 255                 pool->mNumIdleThreads--;
 256
 257                 PRIntervalTime delta = PR_IntervalNow() - start;
 258                 if (delta >= timeout)
 259                     break;
 260                 timeout -= delta;
 261                 start += delta;
 262             }
 263
 264             // if the queue is still empty, then kill this thread (either we
 265             // are shutting down or the thread exceeded the idle timeout)...
 266             if (PR_CLIST_IS_EMPTY(&pool->mEventQ))
 267                 break;
 268
 269             // handle one event at a time: we don't want this one thread to hog
 270             // all the events while other threads may be able to help out ;-)
 271             do {
 272                 PLEvent *event = PLEVENT_FROM_LINK(PR_LIST_HEAD(&pool->mEventQ));
 273                 PR_REMOVE_AND_INIT_LINK(&event->link);
 274
 275                 LOG(("event:%p\n", event));
 276
 277                 // release lock!
 278                 lock.unlock();
 279                 PL_HandleEvent(event);
 280                 lock.lock();
 281             }
 282             while (!PR_CLIST_IS_EMPTY(&pool->mEventQ));
 283         }
 284
 285         // thread is going away...
 286         pool->mNumThreads--;
 287         PR_NotifyCondVar(pool->mExitThreadCV);
 288     }
 289
 290     // release our reference to the pool
 291     NS_RELEASE(pool);
 292
 293     LOG(("leaving ThreadFunc\n"));
 294 }
 295
 296 //-----------------------------------------------------------------------------
 297
 298 NS_METHOD
 299 net_NewIOThreadPool(nsISupports *outer, REFNSIID iid, void **result)
 300 {
 301     nsIOThreadPool *pool = new nsIOThreadPool();
 302     if (!pool)
 303         return NS_ERROR_OUT_OF_MEMORY;
 304     NS_ADDREF(pool);
 305     nsresult rv = pool->Init();
 306     if (NS_SUCCEEDED(rv))
 307         rv = pool->QueryInterface(iid, result);
 308     NS_RELEASE(pool);
 309     return rv;
 310 }