Status: New
Owner: ----
New issue 3960 by [email protected]: Problems with Debug.setBreakPoint on
node.js/io.js
https://code.google.com/p/v8/issues/detail?id=3960
Version: 4.1.0.14, 4.1.0.21, 3.28.73, others
OS: OS X 10.10.2
Architecture: x64
I am using the V8 Debug API from node.js/io.js. Until now, I had been using
Debug.setBreakPointByScriptIdAndPosition, and that was working well enough.
However, I recently started playing with Debug.setBreakPoint and
Debug.setScriptBreakPoint. I believe I have uncovered some interesting
behavior.
Here's a testcase that I adapted from test/mjsunit/debug-breakpoints.js:
test.js:
Debug = require('vm').runInDebugContext('Debug');
Debug.setListener(function(){console.log('Break event');});
function f() {a=1;b=2}
Debug.setBreakPoint(f, 0, 0);
console.log(Debug.showBreakPoints(f));
f();
You should expect the breakpoint to be hit when f is called. The expected
output is:
() {[B0]a=1;b=2}
Break event
However, this is what I get instead:
$ iojs test.js
() {a=1;b=2}
Now if you change 'setBreakPoint(f,0,0)' to 'setBreakPoint(f,2,0)', this is
the output:
$ iojs test2.js
Break event
() {a=1;b=2}
i.e. we hit *some* breakpoint – so some parts of the Debug API are clearly
working. It seems that we managed to set the breakpoint at the
console.log(...) line (2 lines after f – makes sense). But why can't we set
a breakpoint in f itself?
The plot thickens. If you run the original testcase with the
--expose-debug-as option:
$ iojs --expose-debug-as=PrincessButtercup test.js
() {[B0]a=1;b=2}
Break event
So whatever the issue is, adding --expose-debug-as to the command line ends
up working around it.
Since all our Debug API mjsunit testcases run with the --expose-debug-as
option, all those test cases pass.
I suspect this is an issue in the V8 Debug API rather than in node.js/io.js
– the debug API should either uniformly work or uniformly not work.
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