Merge pull request #66745 from ClickHouse/dbg_shared_mutex

Save writer thread id in shared mutex for debugging

src/Common/SharedMutex.cpp

@@ -1,4 +1,5 @@
 #include <Common/SharedMutex.h>
+#include <base/getThreadId.h>
 
 #ifdef OS_LINUX /// Because of futex
 
@@ -12,6 +13,7 @@ namespace DB
 SharedMutex::SharedMutex()
     : state(0)
     , waiters(0)
+    , writer_thread_id(0)
 {}
 
 void SharedMutex::lock()
@@ -29,6 +31,10 @@ void SharedMutex::lock()
             break;
     }
 
+    /// The first step of acquiring the exclusive ownership is finished.
+    /// Now we just wait until all readers release the shared ownership.
+    writer_thread_id.store(getThreadId());
+
     value |= writers;
     while (value & readers)
         futexWaitLowerFetch(state, value);
@@ -37,11 +43,15 @@ void SharedMutex::lock()
 bool SharedMutex::try_lock()
 {
     UInt64 value = 0;
-    return state.compare_exchange_strong(value, writers);
+    bool success = state.compare_exchange_strong(value, writers);
+    if (success)
+        writer_thread_id.store(getThreadId());
+    return success;
 }
 
 void SharedMutex::unlock()
 {
+    writer_thread_id.store(0);
     state.store(0);
     if (waiters)
         futexWakeUpperAll(state);

src/Common/SharedMutex.h

@@ -19,6 +19,8 @@ public:
     ~SharedMutex() = default;
     SharedMutex(const SharedMutex &) = delete;
     SharedMutex & operator=(const SharedMutex &) = delete;
+    SharedMutex(SharedMutex &&) = delete;
+    SharedMutex & operator=(SharedMutex &&) = delete;
 
     // Exclusive ownership
     void lock() TSA_ACQUIRE();
@@ -36,6 +38,8 @@ private:
 
     alignas(64) std::atomic<UInt64> state;
     std::atomic<UInt32> waiters;
+    /// Is set while the lock is held (or is in the process of being acquired) in exclusive mode only to facilitate debugging
+    std::atomic<UInt64> writer_thread_id;
 };
 
 }