Split synchronization mechanisms from util.{h,cpp}

1 files changed, 119 insertions, 0 deletions

diff --git a/src/sync.cpp b/src/sync.cpp
new file mode 100644
index 0000000000..fd9bcb62bc
--- /dev/null
+++ b/src/sync.cpp
@@ -0,0 +1,119 @@
+// Copyright (c) 2011-2012 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#include "sync.h"
+
+
+
+#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 trys to lock in a different order.
+//
+
+struct CLockLocation
+{
+    CLockLocation(const char* pszName, const char* pszFile, int nLine)
+    {
+        mutexName = pszName;
+        sourceFile = pszFile;
+        sourceLine = nLine;
+    }
+
+    std::string ToString() const
+    {
+        return mutexName+"  "+sourceFile+":"+itostr(sourceLine);
+    }
+
+private:
+    std::string mutexName;
+    std::string sourceFile;
+    int sourceLine;
+};
+
+typedef std::vector< std::pair<void*, CLockLocation> > LockStack;
+
+static boost::interprocess::interprocess_mutex dd_mutex;
+static std::map<std::pair<void*, void*>, LockStack> lockorders;
+static boost::thread_specific_ptr<LockStack> lockstack;
+
+
+static void potential_deadlock_detected(const std::pair<void*, void*>& mismatch, const LockStack& s1, const LockStack& s2)
+{
+    printf("POTENTIAL DEADLOCK DETECTED\n");
+    printf("Previous lock order was:\n");
+    BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, s2)
+    {
+        if (i.first == mismatch.first) printf(" (1)");
+        if (i.first == mismatch.second) printf(" (2)");
+        printf(" %s\n", i.second.ToString().c_str());
+    }
+    printf("Current lock order is:\n");
+    BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, s1)
+    {
+        if (i.first == mismatch.first) printf(" (1)");
+        if (i.first == mismatch.second) printf(" (2)");
+        printf(" %s\n", i.second.ToString().c_str());
+    }
+}
+
+static void push_lock(void* c, const CLockLocation& locklocation, bool fTry)
+{
+    bool fOrderOK = true;
+    if (lockstack.get() == NULL)
+        lockstack.reset(new LockStack);
+
+    if (fDebug) printf("Locking: %s\n", locklocation.ToString().c_str());
+    dd_mutex.lock();
+
+    (*lockstack).push_back(std::make_pair(c, locklocation));
+
+    if (!fTry) BOOST_FOREACH(const PAIRTYPE(void*, CLockLocation)& i, (*lockstack))
+    {
+        if (i.first == c) break;
+
+        std::pair<void*, void*> p1 = std::make_pair(i.first, c);
+        if (lockorders.count(p1))
+            continue;
+        lockorders[p1] = (*lockstack);
+
+        std::pair<void*, void*> p2 = std::make_pair(c, i.first);
+        if (lockorders.count(p2))
+        {
+            potential_deadlock_detected(p1, lockorders[p2], lockorders[p1]);
+            break;
+        }
+    }
+    dd_mutex.unlock();
+}
+
+static void pop_lock()
+{
+    if (fDebug) 
+    {
+        const CLockLocation& locklocation = (*lockstack).rbegin()->second;
+        printf("Unlocked: %s\n", locklocation.ToString().c_str());
+    }
+    dd_mutex.lock();
+    (*lockstack).pop_back();
+    dd_mutex.unlock();
+}
+
+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();
+}
+
+#endif /* DEBUG_LOCKORDER */