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[poy <617021@xxxxxxxxxxxxxxxxxx>]

Fixed in DC++ 0.780.

** Changed in: dcplusplus
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/617021

Title:
  Semaphore potentially may underflow and become negative

Status in DC++:
  Fix Released
Status in Linux DC++:
  Confirmed

Bug description:
  As noted in POSIX about pthread_cond_wait, spurious wakeup may occur and predicate should be rechecked after wakeup.
  So the patch.

  diff --git a/client/Semaphore.h b/client/Semaphore.h
  index f89148d..b0c59e5 100644
  --- a/client/Semaphore.h
  +++ b/client/Semaphore.h
  @@ -61,7 +61,7 @@ public:

          bool wait() throw() {
                  Lock l(cs);
  -               if(count == 0) {
  +               while (count == 0) {
                          pthread_cond_wait(&cond, &cs.getMutex());
                  }
                  count--;
  @@ -76,7 +76,10 @@ public:
                          millis+=timev.tv_usec/1000;
                          t.tv_sec = timev.tv_sec + (millis/1000);
                          t.tv_nsec = (millis%1000)*1000*1000;
  -                       int ret = pthread_cond_timedwait(&cond, &cs.getMutex(), &t);
  +                       int ret;
  +                       do {
  +                               ret = pthread_cond_timedwait(&cond, &cs.getMutex(), &t);
  +                       } while (ret==0 && count==0);
                          if(ret != 0) {
                                  return false;
                          }