How Does the C# `lock` Statement Work Under the Hood?

Dive into the inner workings of the lock statement

Developers often use the lock statement to protect code execution when dealing with non-thread-safe objects. But what exactly happens under the hood when multiple threads interact with this protected code?

Deep Dive: Tracking the Execution of lock Statements

In C# 3.0, the lock statement translates to the following code:

var temp = obj;
Monitor.Enter(temp);
try
{
    // 非线程安全代码
}
finally
{
    Monitor.Exit(temp);
}

In C# 4.0, this process has been modified and the generated code is as follows:

bool lockWasTaken = false;
var temp = obj;
try
{
    Monitor.Enter(temp, ref lockWasTaken);
    // 非线程安全代码
}
finally
{
    if (lockWasTaken)
    {
        Monitor.Exit(temp); 
    }
}

Monitor.Enter Function

Monitor.Enter plays a vital role in the functionality of the lock statement. MSDN describes its operation as follows:

" Use Enter to get the Monitor of the object passed as argument. If another thread has already executed a Enter for the object but has not yet executed the corresponding Exit, the current thread will block until another The thread releases the object ”

Essentially, Monitor.Enter guarantees exclusive access to the object. If another thread tries to acquire the same lock, it will be suspended until the lock is released. Multiple calls to Enter from the same thread will not cause blocking, but require the same number of Exit calls to unlock the object and allow the waiting thread to resume execution.

Infinite waiting time

It is worth noting that Monitor.Enter will wait indefinitely for the lock to become available. Unlike some locking mechanisms, it does not enforce a timeout.

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