src/ipc/ReadWriteLock.cc

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