You receive a "Break command failed" error message when you break into a running application by using the Visual C++ debugger (278452)

SYMPTOMS

When you attempt to break into a running application by using the Visual C++ debugger, you may receive the following error message in the output window:

DBG: Break command failed within 3 seconds.
DBG: Potential deadlock. Soft broken.

Any further attempts to step through code are unsuccessful; only Go works to resume the process.

CAUSE

There are two possible causes:

The current thread is suspended. The thread is probably waiting for a synchronization object to become available. Unfortunately, the time-out value in Visual C++ 5.0 and 6.0 is 3 seconds. There is no way to change this time-out value.
The application is performing some CPU-intensive operation. In this case, the debugger has problems breaking into the running process before the time out occurs. This problem seems to happen more frequently on Microsoft Windows 2000.

RESOLUTION

The easiest way to work around this problem is to set breakpoints rather than to perform a hard break at run time. However, there are times when this is not possible.

If you suspect that true deadlock is occurring in your application, you will have to determine its cause. See Detecting Deadlocks in Multithreaded Win32 Applications by Ruediger R. Asche in the Microsoft Developer Library (MSDN) at:

http://msdn.microsoft.com/library/techart/msdn_deadlock.htm

If you suspect that your process just needs more than 3 seconds to wait for the synchronization object, consider setting a breakpoint immediately after the WaitForSingleObject or WaitForMultipleObjects call.

If your application is performing CPU-intensive activity when you need to break, one way to allow for easier debugging is to call the Sleep function. By placing strategic calls to Sleep, you allow the debugger to more successfully break into the running process. For example, you can use a macro that only evaluates to a Sleep call when you are debugging:

#ifdef _DEBUG
#define DEBUGSLEEP Sleep(50)
#else
#define DEBUGSLEEP
#endif

If you continue to have problems when you use the DEBUGSLEEP macro, try increasing the time that you sleep by 50 after each test.

MORE INFORMATION

Steps to Reproduce Behavior

The following two code fragments demonstrate the two possible situations. Notice that the second code fragment may not reproduce the behavior on all computers (it depends on the speed of the computer and the operating system).

Deadlock Example

// Simple deadlock example:
WaitForSingleObject(GetCurrentProcess(), INFINITE);

CPU-Intensive Code

// Infinite loop.
int i = 0;
while (true)
   i++;

In the second example, you may be able to successfully break in by changing the code to use the DEBUGSLEEP macro:

   // Infinite loop.
   int i = 0;
   while (true)
   {
      DEBUGSLEEP;
      i++;
   }