While integrating debugger support into our v8 embedding application it was
discovered that debugger state is not saved/restored when threads are
switched - thus once we step over any such C++ call that temporary unlocks
v8 engine, debugger is not able to stop on next statement and script just
runs without stops.
v8 version 5.8.283.32
* Are there any workarounds to save debug context without modifying v8
souces?
* Why Debug::ArchiveDebug does "Simply reset state. Don't archive anything."
in this case?
Details:
Corresponding source fragment
>
> char* Debug::ArchiveDebug(char* storage) {
> // Simply reset state. Don't archive anything.
> ThreadInit();
> return storage + ArchiveSpacePerThread();
> }
> char* Debug::RestoreDebug(char* storage) {
> // Simply reset state. Don't restore anything.
> ThreadInit();
> return storage + ArchiveSpacePerThread();
> }
> int Debug::ArchiveSpacePerThread() { return 0; }
>
>
Call stack:
<https://lh3.googleusercontent.com/-L_dbS0DO1k8/WRrFuqm3o2I/AAAAAAAAAMw/V8n33pl9l3Qxq37nMAwuTfHGuykepf7kACLcB/s1600/call_stack.bmp>
Actual sequence:
1. While step by step debugging stop on API exported from C++ that does
following
2.a. Unlock v8 via v8::Unlocker
2.b. Set native event
2.c. Meanwhile other C++ thread will wake, lock v8 via v8::Locker, issue JS
callback, unlock v8
2.d. Wait for confirmation from that other C++ thread
2.e. Lock v8 again in destuctor of v8::Unlocker
3. After return from that API debugger does not stop any more because
inside of Debug::Break(JavaScriptFrame* frame)
call to last_step_action(); now returns StepNone instead of
StepNext and JS continues to run instead of stopping on next JS statement.
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