24

Does managed C++ have an equivalent to C#'s lock() and VB's SyncLock? If so, how do I use it?

Jon Cage
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Brian
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4 Answers4

68

C++/CLI does have a lock class. All you need to do is declare a lock variable using stack-based semantics, and it will safely exit the monitor when its destructor is called, e.g.:

#include <msclr\lock.h>
{    
    msclr::lock l(m_lock);

    // Do work

} //destructor of lock is called (exits monitor).

m_lock declaration depends on whether you are synchronising access to an instance or static member.

To protect instance members, use this:

Object^ m_lock = gcnew Object(); // Each class instance has a private lock - 
                                 // protects instance members.

To protect static members, use this:

static Object^ m_lock = gcnew Object(); // Type has a private lock -
                                        // protects static members.
Sereger
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  • Removed 'dangerous stuff' with 'do work' to not distruct people. Thanks for your comments. – Sereger Sep 26 '11 at 13:40
  • I'm not familiar with C++, how do you declare 'x' ? Thanks – Bastiflew Jun 28 '13 at 12:21
  • Rules for 'x' declaration are the same as in C# as described here: http://msdn.microsoft.com/en-us/library/c5kehkcz.aspx. In summary the guideline is: - define it as a private object, if you want to protect an instance variable; - define it as a private static object variable, if you want to protect a static variable (or if the critical section occurs in a static method in the given class). Thanks for your question - I will enhance the answer. – Sereger Jun 29 '13 at 17:41
22

The equivelent to a lock / SyncLock would be to use the Monitor class.

In .NET 1-3.5sp, lock(obj) does:

Monitor.Enter(obj);
try
{
    // Do work
}
finally
{
    Monitor.Exit(obj);
}

As of .NET 4, it will be:

bool taken = false;
try
{
    Monitor.Enter(obj, ref taken);
    // Do work
}
finally
{
    if (taken)
    {
        Monitor.Exit(obj);
    }
}

You could translate this to C++ by doing:

System::Object^ obj = gcnew System::Object();
Monitor::Enter(obj);
try
{
    // Do work
}
finally
{
    Monitor::Exit(obj);
}
Reed Copsey
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    I'd consider http://stackoverflow.com/questions/1369459/cs-lock-in-managed-c/7527111#7527111 superior in that it is both more in C++ nature (RAII) as well as closer to the C# lock keyword – sehe Sep 26 '11 at 08:56
2

There's no equivalent of the lock keyword in C++. You could do this instead:

Monitor::Enter(instanceToLock);
try
{
    // Only one thread could execute this code at a time
}
finally
{
    Monitor::Exit(instanceToLock);
}
Darin Dimitrov
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-2

Try Threading.Monitor. And catch.

ima
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