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sync.cpp
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sync.cpp
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// Copyright (c) 2011-2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <sync.h>
#include <logging.h>
#include <util/strencodings.h>
#include <util/threadnames.h>
#include <tinyformat.h>
#include <cstdio>
#include <map>
#include <set>
#ifdef DEBUG_LOCKCONTENTION
void PrintLockContention(const char *pszName, const char *pszFile, int nLine) {
LogPrintf("LOCKCONTENTION: %s\n", pszName);
LogPrintf("Locker: %s:%d\n", pszFile, nLine);
}
#endif /* DEBUG_LOCKCONTENTION */
#ifdef DEBUG_LOCKORDER
//
// Early deadlock detection.
// Problem being solved:
// Thread 1 locks A, then B, then C
// Thread 2 locks D, then C, then A
// --> may result in deadlock between the two threads, depending on when
// they run.
// Solution implemented here:
// Keep track of pairs of locks: (A before B), (A before C), etc.
// Complain if any thread tries to lock in a different order.
//
struct CLockLocation {
CLockLocation(const char *pszName, const char *pszFile, int nLine,
bool fTryIn, const std::string &thread_name)
: fTry(fTryIn), mutexName(pszName), sourceFile(pszFile),
m_thread_name(thread_name), sourceLine(nLine) {}
std::string ToString() const {
return strprintf("%s %s:%s%s (in thread %s)", mutexName, sourceFile,
itostr(sourceLine), (fTry ? " (TRY)" : ""),
m_thread_name);
}
private:
bool fTry;
std::string mutexName;
std::string sourceFile;
const std::string &m_thread_name;
int sourceLine;
};
typedef std::vector<std::pair<void *, CLockLocation>> LockStack;
typedef std::map<std::pair<void *, void *>, LockStack> LockOrders;
typedef std::set<std::pair<void *, void *>> InvLockOrders;
struct LockData {
// Very ugly hack: as the global constructs and destructors run single
// threaded, we use this boolean to know whether LockData still exists,
// as DeleteLock can get called by global CCriticalSection destructors
// after LockData disappears.
bool available;
LockData() : available(true) {}
~LockData() { available = false; }
LockOrders lockorders;
InvLockOrders invlockorders;
std::mutex dd_mutex;
};
LockData &GetLockData() {
static LockData lockdata;
return lockdata;
}
static thread_local LockStack g_lockstack;
static void
potential_deadlock_detected(const std::pair<void *, void *> &mismatch,
const LockStack &s1, const LockStack &s2) {
LogPrintf("POTENTIAL DEADLOCK DETECTED\n");
LogPrintf("Previous lock order was:\n");
for (const std::pair<void *, CLockLocation> &i : s2) {
if (i.first == mismatch.first) {
LogPrintfToBeContinued(" (1)");
}
if (i.first == mismatch.second) {
LogPrintfToBeContinued(" (2)");
}
LogPrintf(" %s\n", i.second.ToString());
}
LogPrintf("Current lock order is:\n");
for (const std::pair<void *, CLockLocation> &i : s1) {
if (i.first == mismatch.first) {
LogPrintfToBeContinued(" (1)");
}
if (i.first == mismatch.second) {
LogPrintfToBeContinued(" (2)");
}
LogPrintf(" %s\n", i.second.ToString());
}
if (g_debug_lockorder_abort) {
tfm::format(
std::cerr,
"Assertion failed: detected inconsistent lock order at %s:%i, "
"details in debug log.\n",
__FILE__, __LINE__);
abort();
}
throw std::logic_error("potential deadlock detected");
}
static void push_lock(void *c, const CLockLocation &locklocation) {
LockData &lockdata = GetLockData();
std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
g_lockstack.push_back(std::make_pair(c, locklocation));
for (const std::pair<void *, CLockLocation> &i : g_lockstack) {
if (i.first == c) {
break;
}
std::pair<void *, void *> p1 = std::make_pair(i.first, c);
if (lockdata.lockorders.count(p1)) {
continue;
}
lockdata.lockorders.emplace(p1, g_lockstack);
std::pair<void *, void *> p2 = std::make_pair(c, i.first);
lockdata.invlockorders.insert(p2);
if (lockdata.lockorders.count(p2)) {
potential_deadlock_detected(p1, lockdata.lockorders[p2],
lockdata.lockorders[p1]);
}
}
}
static void pop_lock() {
g_lockstack.pop_back();
}
void EnterCritical(const char *pszName, const char *pszFile, int nLine,
void *cs, bool fTry) {
push_lock(cs, CLockLocation(pszName, pszFile, nLine, fTry,
util::ThreadGetInternalName()));
}
void LeaveCritical() {
pop_lock();
}
std::string LocksHeld() {
std::string result;
for (const std::pair<void *, CLockLocation> &i : g_lockstack) {
result += i.second.ToString() + std::string("\n");
}
return result;
}
void AssertLockHeldInternal(const char *pszName, const char *pszFile, int nLine,
void *cs) {
for (const std::pair<void *, CLockLocation> &i : g_lockstack) {
if (i.first == cs) {
return;
}
}
tfm::format(std::cerr,
"Assertion failed: lock %s not held in %s:%i; locks held:\n%s",
pszName, pszFile, nLine, LocksHeld().c_str());
abort();
}
void AssertLockNotHeldInternal(const char *pszName, const char *pszFile,
int nLine, void *cs) {
for (const std::pair<void *, CLockLocation> &i : g_lockstack) {
if (i.first == cs) {
tfm::format(
std::cerr,
"Assertion failed: lock %s held in %s:%i; locks held:\n%s",
pszName, pszFile, nLine, LocksHeld().c_str());
abort();
}
}
}
void DeleteLock(void *cs) {
LockData &lockdata = GetLockData();
if (!lockdata.available) {
// We're already shutting down.
return;
}
std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
std::pair<void *, void *> item = std::make_pair(cs, nullptr);
LockOrders::iterator it = lockdata.lockorders.lower_bound(item);
while (it != lockdata.lockorders.end() && it->first.first == cs) {
std::pair<void *, void *> invitem =
std::make_pair(it->first.second, it->first.first);
lockdata.invlockorders.erase(invitem);
lockdata.lockorders.erase(it++);
}
InvLockOrders::iterator invit = lockdata.invlockorders.lower_bound(item);
while (invit != lockdata.invlockorders.end() && invit->first == cs) {
std::pair<void *, void *> invinvitem =
std::make_pair(invit->second, invit->first);
lockdata.lockorders.erase(invinvitem);
lockdata.invlockorders.erase(invit++);
}
}
bool g_debug_lockorder_abort = true;
#endif /* DEBUG_LOCKORDER */

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