src/ipc/ReadWriteLock.cc

   1 /*
   2  * $Id$
   3  *
   4  * DEBUG: section 54    Interprocess Communication
   5  */
   6
   7 #include "squid.h"
   8
   9 #include "Store.h"
  10 #include "ipc/ReadWriteLock.h"
  11
  12 bool
  13 Ipc::ReadWriteLock::lockShared()
  14 {
  15     ++readers; // this locks "new" writers out
  16     if (!writers) // there are no old writers
  17         return true;
  18     --readers;
  19     return false;
  20 }
  21
  22 bool
  23 Ipc::ReadWriteLock::lockExclusive()
  24 {
  25     if (!writers++) { // we are the first writer + this locks "new" readers out
  26         if (!readers) // there are no old readers
  27             return true;
  28     }
  29     --writers;
  30     return false;
  31 }
  32
  33 void
  34 Ipc::ReadWriteLock::unlockShared()
  35 {
  36     assert(readers-- > 0);
  37 }
  38
  39 void
  40 Ipc::ReadWriteLock::unlockExclusive()
  41 {
  42     assert(writers-- > 0);
  43 }
  44
  45 void
  46 Ipc::ReadWriteLock::switchExclusiveToShared()
  47 {
  48     ++readers; // must be done before we release exclusive control
  49     unlockExclusive();
  50 }
  51
  52 void
  53 Ipc::ReadWriteLock::updateStats(ReadWriteLockStats &stats) const
  54 {
  55     if (readers) {
  56         ++stats.readable;
  57         stats.readers += readers;
  58     } else if (writers) {
  59         ++stats.writeable;
  60         stats.writers += writers;
  61     } else {
  62         ++stats.idle;
  63     }
  64     ++stats.count;
  65 }
  66
  67
  68 /* Ipc::ReadWriteLockStats */
  69
  70 Ipc::ReadWriteLockStats::ReadWriteLockStats()
  71 {
  72     memset(this, 0, sizeof(*this));
  73 }
  74
  75 void
  76 Ipc::ReadWriteLockStats::dump(StoreEntry &e) const
  77 {
  78     storeAppendPrintf(&e, "Available locks: %9d\n", count);
  79
  80     if (!count)
  81         return;
  82
  83     storeAppendPrintf(&e, "Reading: %9d %6.2f%%\n",
  84                       readable, (100.0 * readable / count));
  85     storeAppendPrintf(&e, "Writing: %9d %6.2f%%\n",
  86                       writeable, (100.0 * writeable / count));
  87     storeAppendPrintf(&e, "Idle:    %9d %6.2f%%\n",
  88                       idle, (100.0 * idle / count));
  89
  90     if (readers || writers) {
  91         const int locked = readers + writers;
  92         storeAppendPrintf(&e, "Readers:         %9d %6.2f%%\n",
  93                           readers, (100.0 * readers / locked));
  94         storeAppendPrintf(&e, "Writers:         %9d %6.2f%%\n",
  95                           writers, (100.0 * writers / locked));
  96     }
  97 }