[Mono-dev] Soft Debugger issues (can't suspend threads in wait_for_suspend)

[Virgile Bello]

I am having trouble with mono soft debugger.
- I embed Mono runtime in my program, and I got MonoDevelop to act as
SoftDebugger client
- Mono soft debugger is loading properly (first breakpoint usually works --
if already set beforehand -- I can see callstacks, etc...)
- As soon as I press F5 -- to execute until this breakpoint is reached again
next iteration -- or if I disable/reenable this breakpoint, program hang
(see log)
- Main loop is in C and Mono functions are called regularly.

I traced down the problem to thread(s) not suspending (cf log).
Usually, it seems it is the Finalizer thread (in this case 00002054) that
doesn't get suspended.

In mono sources, I tried to call mono_gc_collect/mono_gc_invoke_finalizers
in the suspend_thread loop. In that case, I can manage to have F5 working
(breakpoint trigger every step inside the loop).
However it doesn't work as soon as I do anything else (such as removing &
adding again the breakpoint).

I remember seeing this problem on more than 1 thread when I had other
threads active (i.e. Waiting for 3(4) threads to suspend...)

Does anyone have an idea? Maybe there is something special to do if Mono
doesn't keep hand (often back to full unmanaged world since main loop is in
C)

Debugger log:
[00000410] Thread started, obj=04702F20, tls=004CDA60.
[00000410] Suspended.
[00000410] Resumed.
[00000410] Suspending vm...
[00000410] Sent event VM_START, suspend=2.
[00000410] Suspended.
[dbg] Agent thread started, pid=00001260
[00002054] Thread started, obj=04702E70, tls=004EC1D8. < Finalizer thread
[00002054] Suspended.
[dbg] Received command VM(VERSION), id=1.
[dbg] Received command VM(SET_PROTOCOL_VERSION), id=2.
[dbg] Protocol version 2.2, client protocol version 2.2.
[dbg] Received command APPDOMAIN(1), id=3.
...............
[00000410] Suspended.
[dbg] Received command TYPE(1), id=1785.
[dbg] Received command TYPE(6), id=1786.
[00002054] Received single step event for suspending.
[00002054] Suspended.
[dbg] Received command VM(RESUME), id=1787.
[00001260] Resuming vm...
[00002054] Resumed.
[00000410] Resumed.
[00000410] Suspending vm...
[00000410] Interrupting 00002054...
[00000410] Sent event TYPE_LOAD, suspend=2.
[00000410] Suspended.
[dbg] Received command TYPE(1), id=1788.
[dbg] Received command TYPE(6), id=1789.
[00002054] Received single step event for suspending.
[00002054] Suspended.
[dbg] Received command VM(RESUME), id=1790.
[00001260] Resuming vm...
[00002054] Resumed.
[00000410] Resumed.
[00000410] Suspending vm...
[00000410] Interrupting 00002054...
[00000410] Sent event TYPE_LOAD, suspend=2.
[00000410] Suspended.
[dbg] Received command TYPE(1), id=1791.
[dbg] Received command TYPE(6), id=1792.
[dbg] Received command VM(RESUME), id=1793.
[00002054] Received single step event for suspending.
[00002054] Suspended.
[00001260] Resuming vm...
[00000410] Resumed.
[00002054] Resumed.
[00000410] Suspending vm...
[00000410] Interrupting 00002054...
[00000410] Sent event TYPE_LOAD, suspend=2.
[00000410] Suspended.
[dbg] Received command TYPE(1), id=1794.
[dbg] Received command TYPE(6), id=1795.
[dbg] Received command VM(RESUME), id=1796.
[00001260] Resuming vm...
[00000410] Resumed.
[00000410] Breakpoint hit, method=Step, offset=0x1e.
[00000410] Suspending vm...
[00000410] Interrupting 00002054...
[00000410] Sent event BREAKPOINT, suspend=2.
[00000410] Suspended.
[dbg] Received command VM(ALL_THREADS), id=1797.
[dbg] Received command THREAD(1), id=1798.
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
Waiting for 1(2) threads to suspend...
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