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 // One Debugger's onPop handler can remove another Debugger's onPop handler.

 var g = newGlobal();

 var dbg1 = new Debugger(g);

 var dbg2 = new Debugger(g);

 var log;

 var frames = [];

 var firstPop = true;

 function handleEnter(frame) {

     log += '(';

     frames.push(frame);

     frame.onPop = function handlePop(completion) {

         log += ')';

         assertEq(completion.return, 42);

         if (firstPop) {

             // We can't say which frame's onPop handler will get called first.

             if (this == frames[0])

                 frames[1].onPop = undefined;

             else

                 frames[0].onPop = undefined;

             gc();

         } else {

             assertEq("second pop handler was called",

                      "second pop handler should not be called");

         }

         firstPop = false;

     };

 };

 dbg1.onEnterFrame = handleEnter;

 dbg2.onEnterFrame = handleEnter;

 log = '';

 assertEq(g.eval('40 + 2'), 42);

 assertEq(log, '(()');