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 <tinyformat.h>
#include <util/strencodings.h>
#include <util/threadnames.h>
 
#include <tinyformat.h>
 
#include <map>
#include <mutex>
#include <set>
#include <system_error>
#include <thread>
#include <type_traits>
#include <unordered_map>
#include <utility>
#include <vector>
 
#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' in %s:%s%s (in thread '%s')", mutexName,
                         sourceFile, sourceLine, (fTry ? " (TRY)" : ""),
                         m_thread_name);
    }
 
    std::string Name() const { return mutexName; }
 
private:
    bool fTry;
    std::string mutexName;
    std::string sourceFile;
    const std::string &m_thread_name;
    int sourceLine;
};
 
using LockStackItem = std::pair<void *, CLockLocation>;
using LockStack = std::vector<LockStackItem>;
using LockStacks = std::unordered_map<std::thread::id, LockStack>;
 
using LockPair = std::pair<void *, void *>;
using LockOrders = std::map<LockPair, LockStack>;
using InvLockOrders = std::set<LockPair>;
 
struct LockData {
    LockStacks m_lock_stacks;
    LockOrders lockorders;
    InvLockOrders invlockorders;
    std::mutex dd_mutex;
};
 
LockData &GetLockData() {
    // This approach guarantees that the object is not destroyed until after its
    // last use. The operating system automatically reclaims all the memory in a
    // program's heap when that program exits.
    // Since the ~LockData() destructor is never called, the LockData class and
    // all its subclasses must have implicitly-defined destructors.
    static LockData &lock_data = *new LockData();
    return lock_data;
}
 
static void potential_deadlock_detected(const LockPair &mismatch,
                                        const LockStack &s1,
                                        const LockStack &s2) {
    LogPrintf("POTENTIAL DEADLOCK DETECTED\n");
    LogPrintf("Previous lock order was:\n");
    for (const LockStackItem &i : s1) {
        if (i.first == mismatch.first) {
            LogPrintfToBeContinued(" (1)");
        }
        if (i.first == mismatch.second) {
            LogPrintfToBeContinued(" (2)");
        }
        LogPrintf(" %s\n", i.second.ToString());
    }
 
    std::string mutex_a, mutex_b;
    LogPrintf("Current lock order is:\n");
    for (const LockStackItem &i : s2) {
        if (i.first == mismatch.first) {
            LogPrintfToBeContinued(" (1)");
            mutex_a = i.second.Name();
        }
        if (i.first == mismatch.second) {
            LogPrintfToBeContinued(" (2)");
            mutex_b = i.second.Name();
        }
        LogPrintf(" %s\n", i.second.ToString());
    }
    if (g_debug_lockorder_abort) {
        tfm::format(
            std::cerr,
            "Assertion failed: detected inconsistent lock order for %s, "
            "details in debug log.\n",
            s2.back().second.ToString());
        abort();
    }
    throw std::logic_error(
        strprintf("potential deadlock detected: %s -> %s -> %s", mutex_b,
                  mutex_a, mutex_b));
}
 
static void double_lock_detected(const void *mutex,
                                 const LockStack &lock_stack) {
    LogPrintf("DOUBLE LOCK DETECTED\n");
    LogPrintf("Lock order:\n");
    for (const LockStackItem &i : lock_stack) {
        if (i.first == mutex) {
            LogPrintfToBeContinued(" (*)");
        }
        LogPrintf(" %s\n", i.second.ToString());
    }
    if (g_debug_lockorder_abort) {
        tfm::format(std::cerr,
                    "Assertion failed: detected double lock for %s, details in "
                    "debug log.\n",
                    lock_stack.back().second.ToString());
        abort();
    }
    throw std::logic_error("double lock detected");
}
 
template <typename MutexType>
static void push_lock(MutexType *c, const CLockLocation &locklocation) {
    constexpr bool is_recursive_mutex =
        std::is_base_of<RecursiveMutex, MutexType>::value ||
        std::is_base_of<std::recursive_mutex, MutexType>::value;
 
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
    LockStack &lock_stack = lockdata.m_lock_stacks[std::this_thread::get_id()];
    lock_stack.emplace_back(c, locklocation);
    for (size_t j = 0; j < lock_stack.size() - 1; ++j) {
        const LockStackItem &i = lock_stack[j];
        if (i.first == c) {
            if (is_recursive_mutex) {
                break;
            }
            // It is not a recursive mutex and it appears in the stack two
            // times: at position `j` and at the end (which we added just
            // before this loop).
            // Can't allow locking the same (non-recursive) mutex two times
            // from the same thread as that results in an undefined behavior.
            auto lock_stack_copy = lock_stack;
            lock_stack.pop_back();
            double_lock_detected(c, lock_stack_copy);
            // double_lock_detected() does not return.
        }
 
        const LockPair p1 = std::make_pair(i.first, c);
        if (lockdata.lockorders.count(p1)) {
            continue;
        }
 
        const LockPair p2 = std::make_pair(c, i.first);
        if (lockdata.lockorders.count(p2)) {
            auto lock_stack_copy = lock_stack;
            lock_stack.pop_back();
            potential_deadlock_detected(p1, lockdata.lockorders[p2],
                                        lock_stack_copy);
            // potential_deadlock_detected() does not return.
        }
 
        lockdata.lockorders.emplace(p1, lock_stack);
        lockdata.invlockorders.insert(p2);
    }
}
 
static void pop_lock() {
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
    LockStack &lock_stack = lockdata.m_lock_stacks[std::this_thread::get_id()];
    lock_stack.pop_back();
    if (lock_stack.empty()) {
        lockdata.m_lock_stacks.erase(std::this_thread::get_id());
    }
}
 
template <typename MutexType>
void EnterCritical(const char *pszName, const char *pszFile, int nLine,
                   MutexType *cs, bool fTry) {
    push_lock(cs, CLockLocation(pszName, pszFile, nLine, fTry,
                                util::ThreadGetInternalName()));
}
template void EnterCritical(const char *, const char *, int, Mutex *, bool);
template void EnterCritical(const char *, const char *, int, RecursiveMutex *,
                            bool);
template void EnterCritical(const char *, const char *, int, std::mutex *,
                            bool);
template void EnterCritical(const char *, const char *, int,
                            std::recursive_mutex *, bool);
 
void CheckLastCritical(void *cs, std::string &lockname, const char *guardname,
                       const char *file, int line) {
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
    const LockStack &lock_stack =
        lockdata.m_lock_stacks[std::this_thread::get_id()];
    if (!lock_stack.empty()) {
        const auto &lastlock = lock_stack.back();
        if (lastlock.first == cs) {
            lockname = lastlock.second.Name();
            return;
        }
    }
 
    LogPrintf("INCONSISTENT LOCK ORDER DETECTED\n");
    LogPrintf("Current lock order (least recent first) is:\n");
    for (const LockStackItem &i : lock_stack) {
        LogPrintf(" %s\n", i.second.ToString());
    }
    if (g_debug_lockorder_abort) {
        tfm::format(std::cerr,
                    "%s:%s %s was not most recent critical section locked, "
                    "details in debug log.\n",
                    file, line, guardname);
        abort();
    }
    throw std::logic_error(
        strprintf("%s was not most recent critical section locked", guardname));
}
 
void LeaveCritical() {
    pop_lock();
}
 
std::string LocksHeld() {
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
    const LockStack &lock_stack =
        lockdata.m_lock_stacks[std::this_thread::get_id()];
    std::string result;
    for (const LockStackItem &i : lock_stack) {
        result += i.second.ToString() + std::string("\n");
    }
    return result;
}
 
static bool LockHeld(void *mutex) {
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
    const LockStack &lock_stack =
        lockdata.m_lock_stacks[std::this_thread::get_id()];
    for (const LockStackItem &i : lock_stack) {
        if (i.first == mutex) {
            return true;
        }
    }
 
    return false;
}
 
template <typename MutexType>
void AssertLockHeldInternal(const char *pszName, const char *pszFile, int nLine,
                            MutexType *cs) {
    if (LockHeld(cs)) {
        return;
    }
    tfm::format(std::cerr,
                "Assertion failed: lock %s not held in %s:%i; locks held:\n%s",
                pszName, pszFile, nLine, LocksHeld());
    abort();
}
template void AssertLockHeldInternal(const char *, const char *, int, Mutex *);
template void AssertLockHeldInternal(const char *, const char *, int,
                                     RecursiveMutex *);
 
template <typename MutexType>
void AssertLockNotHeldInternal(const char *pszName, const char *pszFile,
                               int nLine, MutexType *cs) {
    if (!LockHeld(cs)) {
        return;
    }
    tfm::format(std::cerr,
                "Assertion failed: lock %s held in %s:%i; locks held:\n%s",
                pszName, pszFile, nLine, LocksHeld());
    abort();
}
template void AssertLockNotHeldInternal(const char *, const char *, int,
                                        Mutex *);
template void AssertLockNotHeldInternal(const char *, const char *, int,
                                        RecursiveMutex *);
 
void DeleteLock(void *cs) {
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
    const LockPair item = std::make_pair(cs, nullptr);
    LockOrders::iterator it = lockdata.lockorders.lower_bound(item);
    while (it != lockdata.lockorders.end() && it->first.first == cs) {
        const LockPair 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) {
        const LockPair invinvitem = std::make_pair(invit->second, invit->first);
        lockdata.lockorders.erase(invinvitem);
        lockdata.invlockorders.erase(invit++);
    }
}
 
bool LockStackEmpty() {
    LockData &lockdata = GetLockData();
    std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
    const auto it = lockdata.m_lock_stacks.find(std::this_thread::get_id());
    if (it == lockdata.m_lock_stacks.end()) {
        return true;
    }
    return it->second.empty();
}
 
bool g_debug_lockorder_abort = true;
 
#endif /* DEBUG_LOCKORDER */