src/ipc/ReadWriteLock.cc

   1 /*
   2  * Copyright (C) 1996-2014 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 /* DEBUG: section 54    Interprocess Communication */
  10
  11 #include "squid.h"
  12 #include "ipc/ReadWriteLock.h"
  13 #include "Store.h"
  14
  15 bool
  16 Ipc::ReadWriteLock::lockShared()
  17 {
  18     ++readLevel; // this locks "new" writers out
  19     if (!writeLevel || appending) { // nobody is writing, or sharing is OK
  20         ++readers;
  21         return true;
  22     }
  23     --readLevel;
  24     return false;
  25 }
  26
  27 bool
  28 Ipc::ReadWriteLock::lockExclusive()
  29 {
  30     if (!writeLevel++) { // we are the first writer + lock "new" readers out
  31         if (!readLevel) { // no old readers and nobody is becoming one
  32             writing = true;
  33             return true;
  34         }
  35     }
  36     --writeLevel;
  37     return false;
  38 }
  39
  40 void
  41 Ipc::ReadWriteLock::unlockShared()
  42 {
  43     assert(readers > 0);
  44     --readers;
  45     --readLevel;
  46 }
  47
  48 void
  49 Ipc::ReadWriteLock::unlockExclusive()
  50 {
  51     assert(writing);
  52     appending = false;
  53     writing = false;
  54     --writeLevel;
  55 }
  56
  57 void
  58 Ipc::ReadWriteLock::switchExclusiveToShared()
  59 {
  60     assert(writing);
  61     ++readLevel; // must be done before we release exclusive control
  62     ++readers;
  63     unlockExclusive();
  64 }
  65
  66 void
  67 Ipc::ReadWriteLock::startAppending()
  68 {
  69     assert(writing);
  70     appending = true;
  71 }
  72
  73 void
  74 Ipc::ReadWriteLock::updateStats(ReadWriteLockStats &stats) const
  75 {
  76     if (readers) {
  77         ++stats.readable;
  78         stats.readers += readers;
  79     } else if (writing) {
  80         ++stats.writeable;
  81         ++stats.writers;
  82         stats.appenders += appending;
  83     } else {
  84         ++stats.idle;
  85     }
  86     ++stats.count;
  87 }
  88
  89 /* Ipc::ReadWriteLockStats */
  90
  91 Ipc::ReadWriteLockStats::ReadWriteLockStats()
  92 {
  93     memset(this, 0, sizeof(*this));
  94 }
  95
  96 void
  97 Ipc::ReadWriteLockStats::dump(StoreEntry &e) const
  98 {
  99     storeAppendPrintf(&e, "Available locks: %9d\n", count);
 100
 101     if (!count)
 102         return;
 103
 104     storeAppendPrintf(&e, "Reading: %9d %6.2f%%\n",
 105                       readable, (100.0 * readable / count));
 106     storeAppendPrintf(&e, "Writing: %9d %6.2f%%\n",
 107                       writeable, (100.0 * writeable / count));
 108     storeAppendPrintf(&e, "Idle:    %9d %6.2f%%\n",
 109                       idle, (100.0 * idle / count));
 110
 111     if (readers || writers) {
 112         const int locked = readers + writers;
 113         storeAppendPrintf(&e, "Readers:         %9d %6.2f%%\n",
 114                           readers, (100.0 * readers / locked));
 115         const double appPerc = writers ? (100.0 * appenders / writers) : 0.0;
 116         storeAppendPrintf(&e, "Writers:         %9d %6.2f%% including Appenders: %9d %6.2f%%\n",
 117                           writers, (100.0 * writers / locked),
 118                           appenders, appPerc);
 119     }
 120 }