src/ipc/ReadWriteLock.cc

   1 /*
   2  * DEBUG: section 54    Interprocess Communication
   3  */
   4
   5 #include "squid.h"
   6 #include "ipc/ReadWriteLock.h"
   7 #include "Store.h"
   8
   9 bool
  10 Ipc::ReadWriteLock::lockShared()
  11 {
  12     ++readLevel; // this locks "new" writers out
  13     if (!writeLevel || appending) { // nobody is writing, or sharing is OK
  14         ++readers;
  15         return true;
  16     }
  17     --readLevel;
  18     return false;
  19 }
  20
  21 bool
  22 Ipc::ReadWriteLock::lockExclusive()
  23 {
  24     if (!writeLevel++) { // we are the first writer + lock "new" readers out
  25         if (!readLevel) { // no old readers and nobody is becoming one
  26             writing = true;
  27             return true;
  28         }
  29     }
  30     --writeLevel;
  31     return false;
  32 }
  33
  34 void
  35 Ipc::ReadWriteLock::unlockShared()
  36 {
  37     assert(readers > 0);
  38     --readers;
  39     --readLevel;
  40 }
  41
  42 void
  43 Ipc::ReadWriteLock::unlockExclusive()
  44 {
  45     assert(writing);
  46     appending = false;
  47     writing = false;
  48     --writeLevel;
  49 }
  50
  51 void
  52 Ipc::ReadWriteLock::switchExclusiveToShared()
  53 {
  54     assert(writing);
  55     ++readLevel; // must be done before we release exclusive control
  56     ++readers;
  57     unlockExclusive();
  58 }
  59
  60 void
  61 Ipc::ReadWriteLock::startAppending()
  62 {
  63     assert(writing);
  64     appending = true;
  65 }
  66
  67 void
  68 Ipc::ReadWriteLock::updateStats(ReadWriteLockStats &stats) const
  69 {
  70     if (readers) {
  71         ++stats.readable;
  72         stats.readers += readers;
  73     } else if (writing) {
  74         ++stats.writeable;
  75         ++stats.writers;
  76         stats.appenders += appending;
  77     } else {
  78         ++stats.idle;
  79     }
  80     ++stats.count;
  81 }
  82
  83 /* Ipc::ReadWriteLockStats */
  84
  85 Ipc::ReadWriteLockStats::ReadWriteLockStats()
  86 {
  87     memset(this, 0, sizeof(*this));
  88 }
  89
  90 void
  91 Ipc::ReadWriteLockStats::dump(StoreEntry &e) const
  92 {
  93     storeAppendPrintf(&e, "Available locks: %9d\n", count);
  94
  95     if (!count)
  96         return;
  97
  98     storeAppendPrintf(&e, "Reading: %9d %6.2f%%\n",
  99                       readable, (100.0 * readable / count));
 100     storeAppendPrintf(&e, "Writing: %9d %6.2f%%\n",
 101                       writeable, (100.0 * writeable / count));
 102     storeAppendPrintf(&e, "Idle:    %9d %6.2f%%\n",
 103                       idle, (100.0 * idle / count));
 104
 105     if (readers || writers) {
 106         const int locked = readers + writers;
 107         storeAppendPrintf(&e, "Readers:         %9d %6.2f%%\n",
 108                           readers, (100.0 * readers / locked));
 109         const double appPerc = writers ? (100.0 * appenders / writers) : 0.0;
 110         storeAppendPrintf(&e, "Writers:         %9d %6.2f%% including Appenders: %9d %6.2f%%\n",
 111                           writers, (100.0 * writers / locked),
 112                           appenders, appPerc);
 113     }
 114 }