diff --git a/src/sync.cpp b/src/sync.cpp
index 3b5db85b7..1a432bfda 100644
--- a/src/sync.cpp
+++ b/src/sync.cpp
@@ -1,185 +1,197 @@
 // 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 "util.h"
 #include "utilstrencodings.h"
 
 #include <cstdio>
 #include <set>
 
 #ifdef DEBUG_LOCKCONTENTION
 #if !defined(HAVE_THREAD_LOCAL)
 static_assert(false, "thread_local is not supported");
 #endif
 
 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) {
         mutexName = pszName;
         sourceFile = pszFile;
         sourceLine = nLine;
         fTry = fTryIn;
     }
 
     std::string ToString() const {
         return mutexName + "  " + sourceFile + ":" + itostr(sourceLine) +
                (fTry ? " (TRY)" : "");
     }
 
 private:
     bool fTry;
     std::string mutexName;
     std::string sourceFile;
     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;
 } static lockdata;
 
 static thread_local std::unique_ptr<LockStack> 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) {
             LogPrintf(" (1)");
         }
         if (i.first == mismatch.second) {
             LogPrintf(" (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) {
             LogPrintf(" (1)");
         }
         if (i.first == mismatch.second) {
             LogPrintf(" (2)");
         }
         LogPrintf(" %s\n", i.second.ToString());
     }
     assert(false);
 }
 
 static void push_lock(void *c, const CLockLocation &locklocation) {
     if (!lockstack) {
         lockstack.reset(new LockStack);
     }
 
     std::lock_guard<std::mutex> lock(lockdata.dd_mutex);
 
     lockstack->push_back(std::make_pair(c, locklocation));
 
     for (const std::pair<void *, CLockLocation> &i : (*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[p1] = (*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() {
     (*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));
 }
 
 void LeaveCritical() {
     pop_lock();
 }
 
 std::string LocksHeld() {
     std::string result;
     for (const std::pair<void *, CLockLocation> &i : *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 : *lockstack) {
         if (i.first == cs) return;
     }
     fprintf(stderr,
             "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 : *lockstack) {
+        if (i.first == cs) {
+            fprintf(stderr,
+                    "Assertion failed: lock %s held in %s:%i; locks held:\n%s",
+                    pszName, pszFile, nLine, LocksHeld().c_str());
+            abort();
+        }
+    }
+}
+
 void DeleteLock(void *cs) {
     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++);
     }
 }
 
 #endif /* DEBUG_LOCKORDER */
diff --git a/src/sync.h b/src/sync.h
index cd0df5cc6..a18ffab5d 100644
--- a/src/sync.h
+++ b/src/sync.h
@@ -1,265 +1,272 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
 // Copyright (c) 2009-2016 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #ifndef BITCOIN_SYNC_H
 #define BITCOIN_SYNC_H
 
 #include "threadsafety.h"
 
 #include <condition_variable>
 #include <mutex>
 #include <thread>
 
 /////////////////////////////////////////////////
 //                                             //
 // THE SIMPLE DEFINITION, EXCLUDING DEBUG CODE //
 //                                             //
 /////////////////////////////////////////////////
 
 /*
 CCriticalSection mutex;
     std::recursive_mutex mutex;
 
 LOCK(mutex);
     std::unique_lock<std::recursive_mutex> criticalblock(mutex);
 
 LOCK2(mutex1, mutex2);
     std::unique_lock<std::recursive_mutex> criticalblock1(mutex1);
     std::unique_lock<std::recursive_mutex> criticalblock2(mutex2);
 
 TRY_LOCK(mutex, name);
     std::unique_lock<std::recursive_mutex> name(mutex, std::try_to_lock_t);
 
 ENTER_CRITICAL_SECTION(mutex); // no RAII
     mutex.lock();
 
 LEAVE_CRITICAL_SECTION(mutex); // no RAII
     mutex.unlock();
  */
 
 ///////////////////////////////
 //                           //
 // THE ACTUAL IMPLEMENTATION //
 //                           //
 ///////////////////////////////
 
 /**
  * Template mixin that adds -Wthread-safety locking
  * annotations to a subset of the mutex API.
  */
 template <typename PARENT> class LOCKABLE AnnotatedMixin : public PARENT {
 public:
     void lock() EXCLUSIVE_LOCK_FUNCTION() { PARENT::lock(); }
 
     void unlock() UNLOCK_FUNCTION() { PARENT::unlock(); }
 
     bool try_lock() EXCLUSIVE_TRYLOCK_FUNCTION(true) {
         return PARENT::try_lock();
     }
 };
 
 #ifdef DEBUG_LOCKORDER
 void EnterCritical(const char *pszName, const char *pszFile, int nLine,
                    void *cs, bool fTry = false);
 void LeaveCritical();
 std::string LocksHeld();
 void AssertLockHeldInternal(const char *pszName, const char *pszFile, int nLine,
                             void *cs);
+void AssertLockNotHeldInternal(const char *pszName, const char *pszFile,
+                               int nLine, void *cs);
 void DeleteLock(void *cs);
 #else
 static inline void EnterCritical(const char *pszName, const char *pszFile,
                                  int nLine, void *cs, bool fTry = false) {}
 static inline void LeaveCritical() {}
 static inline void AssertLockHeldInternal(const char *pszName,
                                           const char *pszFile, int nLine,
                                           void *cs) {}
+static inline void AssertLockNotHeldInternal(const char *pszName,
+                                             const char *pszFile, int nLine,
+                                             void *cs) {}
 static inline void DeleteLock(void *cs) {}
 #endif
 #define AssertLockHeld(cs) AssertLockHeldInternal(#cs, __FILE__, __LINE__, &cs)
+#define AssertLockNotHeld(cs)                                                  \
+    AssertLockNotHeldInternal(#cs, __FILE__, __LINE__, &cs)
 
 /**
  * Wrapped mutex: supports recursive locking, but no waiting
  * TODO: We should move away from using the recursive lock by default.
  */
 class CCriticalSection : public AnnotatedMixin<std::recursive_mutex> {
 public:
     ~CCriticalSection() { DeleteLock((void *)this); }
 };
 
 /** Wrapped mutex: supports waiting but not recursive locking */
 typedef AnnotatedMixin<std::mutex> CWaitableCriticalSection;
 
 /**
  * Just a typedef for std::condition_variable, can be wrapped later if desired.
  */
 typedef std::condition_variable CConditionVariable;
 
 /**
  * Just a typedef for std::unique_lock, can be wrapped later if desired.
  */
 typedef std::unique_lock<std::mutex> WaitableLock;
 
 #ifdef DEBUG_LOCKCONTENTION
 void PrintLockContention(const char *pszName, const char *pszFile, int nLine);
 #endif
 
 /** Wrapper around std::unique_lock<CCriticalSection> */
 class SCOPED_LOCKABLE CCriticalBlock {
 private:
     std::unique_lock<CCriticalSection> lock;
 
     void Enter(const char *pszName, const char *pszFile, int nLine) {
         EnterCritical(pszName, pszFile, nLine, (void *)(lock.mutex()));
 #ifdef DEBUG_LOCKCONTENTION
         if (!lock.try_lock()) {
             PrintLockContention(pszName, pszFile, nLine);
 #endif
             lock.lock();
 #ifdef DEBUG_LOCKCONTENTION
         }
 #endif
     }
 
     bool TryEnter(const char *pszName, const char *pszFile, int nLine) {
         EnterCritical(pszName, pszFile, nLine, (void *)(lock.mutex()), true);
         lock.try_lock();
         if (!lock.owns_lock()) LeaveCritical();
         return lock.owns_lock();
     }
 
 public:
     CCriticalBlock(CCriticalSection &mutexIn, const char *pszName,
                    const char *pszFile, int nLine, bool fTry = false)
         EXCLUSIVE_LOCK_FUNCTION(mutexIn)
         : lock(mutexIn, std::defer_lock) {
         if (fTry)
             TryEnter(pszName, pszFile, nLine);
         else
             Enter(pszName, pszFile, nLine);
     }
 
     CCriticalBlock(CCriticalSection *pmutexIn, const char *pszName,
                    const char *pszFile, int nLine, bool fTry = false)
         EXCLUSIVE_LOCK_FUNCTION(pmutexIn) {
         if (!pmutexIn) return;
 
         lock = std::unique_lock<CCriticalSection>(*pmutexIn, std::defer_lock);
         if (fTry)
             TryEnter(pszName, pszFile, nLine);
         else
             Enter(pszName, pszFile, nLine);
     }
 
     ~CCriticalBlock() UNLOCK_FUNCTION() {
         if (lock.owns_lock()) LeaveCritical();
     }
 
     operator bool() { return lock.owns_lock(); }
 };
 
 #define PASTE(x, y) x##y
 #define PASTE2(x, y) PASTE(x, y)
 
 #define LOCK(cs)                                                               \
     CCriticalBlock PASTE2(criticalblock, __COUNTER__)(cs, #cs, __FILE__,       \
                                                       __LINE__)
 #define LOCK2(cs1, cs2)                                                        \
     CCriticalBlock criticalblock1(cs1, #cs1, __FILE__, __LINE__),              \
         criticalblock2(cs2, #cs2, __FILE__, __LINE__)
 #define TRY_LOCK(cs, name)                                                     \
     CCriticalBlock name(cs, #cs, __FILE__, __LINE__, true)
 
 #define ENTER_CRITICAL_SECTION(cs)                                             \
     {                                                                          \
         EnterCritical(#cs, __FILE__, __LINE__, (void *)(&cs));                 \
         (cs).lock();                                                           \
     }
 
 #define LEAVE_CRITICAL_SECTION(cs)                                             \
     {                                                                          \
         (cs).unlock();                                                         \
         LeaveCritical();                                                       \
     }
 
 class CSemaphore {
 private:
     std::condition_variable condition;
     std::mutex mutex;
     int value;
 
 public:
     CSemaphore(int init) : value(init) {}
 
     void wait() {
         std::unique_lock<std::mutex> lock(mutex);
         condition.wait(lock, [&]() { return value >= 1; });
         value--;
     }
 
     bool try_wait() {
         std::lock_guard<std::mutex> lock(mutex);
         if (value < 1) {
             return false;
         }
         value--;
         return true;
     }
 
     void post() {
         {
             std::lock_guard<std::mutex> lock(mutex);
             value++;
         }
         condition.notify_one();
     }
 };
 
 /** RAII-style semaphore lock */
 class CSemaphoreGrant {
 private:
     CSemaphore *sem;
     bool fHaveGrant;
 
 public:
     void Acquire() {
         if (fHaveGrant) return;
         sem->wait();
         fHaveGrant = true;
     }
 
     void Release() {
         if (!fHaveGrant) return;
         sem->post();
         fHaveGrant = false;
     }
 
     bool TryAcquire() {
         if (!fHaveGrant && sem->try_wait()) fHaveGrant = true;
         return fHaveGrant;
     }
 
     void MoveTo(CSemaphoreGrant &grant) {
         grant.Release();
         grant.sem = sem;
         grant.fHaveGrant = fHaveGrant;
         fHaveGrant = false;
     }
 
     CSemaphoreGrant() : sem(nullptr), fHaveGrant(false) {}
 
     CSemaphoreGrant(CSemaphore &sema, bool fTry = false)
         : sem(&sema), fHaveGrant(false) {
         if (fTry)
             TryAcquire();
         else
             Acquire();
     }
 
     ~CSemaphoreGrant() { Release(); }
 
     operator bool() { return fHaveGrant; }
 };
 
 #endif // BITCOIN_SYNC_H