src/sync.cpp

   1 // Copyright (c) 2011-2015 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #include "sync.h"
   6
   7 #include "util.h"
   8 #include "utilstrencodings.h"
   9
  10 #include <stdio.h>
  11
  12 #include <boost/foreach.hpp>
  13 #include <boost/thread.hpp>
  14
  15 #ifdef DEBUG_LOCKCONTENTION
  16 void PrintLockContention(const char* pszName, const char* pszFile, int nLine)
  17 {
  18     LogPrintf("LOCKCONTENTION: %s\n", pszName);
  19     LogPrintf("Locker: %s:%d\n", pszFile, nLine);
  20 }
  21 #endif /* DEBUG_LOCKCONTENTION */
  22
  23 #ifdef DEBUG_LOCKORDER
  24 //
  25 // Early deadlock detection.
  26 // Problem being solved:
  27 //    Thread 1 locks  A, then B, then C
  28 //    Thread 2 locks  D, then C, then A
  29 //     --> may result in deadlock between the two threads, depending on when they run.
  30 // Solution implemented here:
  31 // Keep track of pairs of locks: (A before B), (A before C), etc.
  32 // Complain if any thread tries to lock in a different order.
  33 //
  34
  35 struct CLockLocation {
  36     CLockLocation(const char* pszName, const char* pszFile, int nLine, bool fTryIn)
  37     {
  38         mutexName = pszName;
  39         sourceFile = pszFile;
  40         sourceLine = nLine;
  41         fTry = fTryIn;
  42     }
  43
  44     std::string ToString() const
  45     {
  46         return mutexName + "  " + sourceFile + ":" + itostr(sourceLine) + (fTry ? " (TRY)" : "");
  47     }
  48
  49     std::string MutexName() const { return mutexName; }
  50
  51     bool fTry;
  52 private:
  53     std::string mutexName;
  54     std::string sourceFile;
  55     int sourceLine;
  56 };
  57
  58 typedef std::vector<std::pair<void*, CLockLocation> > LockStack;
  59 typedef std::map<std::pair<void*, void*>, LockStack> LockOrders;
  60 typedef std::set<std::pair<void*, void*> > InvLockOrders;
  61
  62 struct LockData {
  63     // Very ugly hack: as the global constructs and destructors run single
  64     // threaded, we use this boolean to know whether LockData still exists,
  65     // as DeleteLock can get called by global CCriticalSection destructors
  66     // after LockData disappears.
  67     bool available;
  68     LockData() : available(true) {}
  69     ~LockData() { available = false; }
  70
  71     LockOrders lockorders;
  72     InvLockOrders invlockorders;
  73     boost::mutex dd_mutex;
  74 } static lockdata;
  75
  76 boost::thread_specific_ptr<LockStack> lockstack;
  77
  78 static void potential_deadlock_detected(const std::pair<void*, void*>& mismatch, const LockStack& s1, const LockStack& s2)
  79 {
  80     // We attempt to not assert on probably-not deadlocks by assuming that
  81     // a try lock will immediately have otherwise bailed if it had
  82     // failed to get the lock
  83     // We do this by, for the locks which triggered the potential deadlock,
  84     // in either lockorder, checking that the second of the two which is locked
  85     // is only a TRY_LOCK, ignoring locks if they are reentrant.
  86     bool firstLocked = false;
  87     bool secondLocked = false;
  88     bool onlyMaybeDeadlock = false;
  89
  90     LogPrintf("POTENTIAL DEADLOCK DETECTED\n");
  91     LogPrintf("Previous lock order was:\n");
  92     BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, s2) {
  93         if (i.first == mismatch.first) {
  94             LogPrintf(" (1)");
  95             if (!firstLocked && secondLocked && i.second.fTry)
  96                 onlyMaybeDeadlock = true;
  97             firstLocked = true;
  98         }
  99         if (i.first == mismatch.second) {
 100             LogPrintf(" (2)");
 101             if (!secondLocked && firstLocked && i.second.fTry)
 102                 onlyMaybeDeadlock = true;
 103             secondLocked = true;
 104         }
 105         LogPrintf(" %s\n", i.second.ToString());
 106     }
 107     firstLocked = false;
 108     secondLocked = false;
 109     LogPrintf("Current lock order is:\n");
 110     BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, s1) {
 111         if (i.first == mismatch.first) {
 112             LogPrintf(" (1)");
 113             if (!firstLocked && secondLocked && i.second.fTry)
 114                 onlyMaybeDeadlock = true;
 115             firstLocked = true;
 116         }
 117         if (i.first == mismatch.second) {
 118             LogPrintf(" (2)");
 119             if (!secondLocked && firstLocked && i.second.fTry)
 120                 onlyMaybeDeadlock = true;
 121             secondLocked = true;
 122         }
 123         LogPrintf(" %s\n", i.second.ToString());
 124     }
 125     assert(onlyMaybeDeadlock);
 126 }
 127
 128 static void push_lock(void* c, const CLockLocation& locklocation, bool fTry)
 129 {
 130     if (lockstack.get() == NULL)
 131         lockstack.reset(new LockStack);
 132
 133     boost::unique_lock<boost::mutex> lock(lockdata.dd_mutex);
 134
 135     (*lockstack).push_back(std::make_pair(c, locklocation));
 136
 137     if (!fTry) {
 138         BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, (*lockstack)) {
 139             if (i.first == c)
 140                 break;
 141
 142             std::pair<void*, void*> p1 = std::make_pair(i.first, c);
 143             if (lockdata.lockorders.count(p1))
 144                 continue;
 145             lockdata.lockorders[p1] = (*lockstack);
 146
 147             std::pair<void*, void*> p2 = std::make_pair(c, i.first);
 148             lockdata.invlockorders.insert(p2);
 149             if (lockdata.lockorders.count(p2))
 150                 potential_deadlock_detected(p1, lockdata.lockorders[p2], lockdata.lockorders[p1]);
 151         }
 152     }
 153 }
 154
 155 static void pop_lock()
 156 {
 157     (*lockstack).pop_back();
 158 }
 159
 160 void EnterCritical(const char* pszName, const char* pszFile, int nLine, void* cs, bool fTry)
 161 {
 162     push_lock(cs, CLockLocation(pszName, pszFile, nLine, fTry), fTry);
 163 }
 164
 165 void LeaveCritical()
 166 {
 167     pop_lock();
 168 }
 169
 170 std::string LocksHeld()
 171 {
 172     std::string result;
 173     BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, *lockstack)
 174         result += i.second.ToString() + std::string("\n");
 175     return result;
 176 }
 177
 178 void AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs)
 179 {
 180     BOOST_FOREACH (const PAIRTYPE(void*, CLockLocation) & i, *lockstack)
 181         if (i.first == cs)
 182             return;
 183     fprintf(stderr, "Assertion failed: lock %s not held in %s:%i; locks held:\n%s", pszName, pszFile, nLine, LocksHeld().c_str());
 184     abort();
 185 }
 186
 187 void DeleteLock(void* cs)
 188 {
 189     if (!lockdata.available) {
 190         // We're already shutting down.
 191         return;
 192     }
 193     boost::unique_lock<boost::mutex> lock(lockdata.dd_mutex);
 194     std::pair<void*, void*> item = std::make_pair(cs, (void*)0);
 195     LockOrders::iterator it = lockdata.lockorders.lower_bound(item);
 196     while (it != lockdata.lockorders.end() && it->first.first == cs) {
 197         std::pair<void*, void*> invitem = std::make_pair(it->first.second, it->first.first);
 198         lockdata.invlockorders.erase(invitem);
 199         lockdata.lockorders.erase(it++);
 200     }
 201     InvLockOrders::iterator invit = lockdata.invlockorders.lower_bound(item);
 202     while (invit != lockdata.invlockorders.end() && invit->first == cs) {
 203         std::pair<void*, void*> invinvitem = std::make_pair(invit->second, invit->first);
 204         lockdata.lockorders.erase(invinvitem);
 205         lockdata.invlockorders.erase(invit++);
 206     }
 207 }
 208
 209 #endif /* DEBUG_LOCKORDER */