Change handling of debugger unloading

Change handling of debugger unloading.

Add a semaphore for accessing debugger varaibles which can be changed from a different thread. This is mainly the debug message handler which can be set to NULL to disconnect the debugger.

Control the unloading of the debugger from the V8 thread. Before the debugger unload was called from the thread setting the debug message handler to NULL. This was not safe as this involves calling into V8. This change handles the unloading of the debugger either when entering a debugger event and the debugger was disconnected while the debugger was not active or when leaving the debugger and the debugger was disconnected while the debugger was active.

Add a flag to avoid unloading the debugger if debugger code is used by the application for other purposes than debugging.

Added tests for clearing the debug message handler.

Committed: http://code.google.com/p/v8/source/detail?r=1648

[Mads Ager (chromium), 2009-03-31 11:08:06]

LGTM

http://codereview.chromium.org/56102/diff/6/1006
File src/debug.h (right):

http://codereview.chromium.org/56102/diff/6/1006#newcode508
Line 508: // No debugger currently active unload the debugger if possible.
Hard to read.  How about:

Unload the debugger if possible. Only called when no debugger is currently
active.

http://codereview.chromium.org/56102/diff/6/1005
File test/cctest/test-debug.cc (right):

http://codereview.chromium.org/56102/diff/6/1005#newcode3774
Line 3774: // Debugger message handler which counts then number of times it is
called.
then -> the

[Søren Thygesen Gjesse, 2009-03-31 11:17:06]

http://codereview.chromium.org/56102/diff/6/1006
File src/debug.h (right):

http://codereview.chromium.org/56102/diff/6/1006#newcode508
Line 508: // No debugger currently active unload the debugger if possible.
On 2009/03/31 11:08:06, Mads Ager wrote:
> Hard to read.  How about:
> 
> Unload the debugger if possible. Only called when no debugger is currently
> active.

Done.

http://codereview.chromium.org/56102/diff/6/1005
File test/cctest/test-debug.cc (right):

http://codereview.chromium.org/56102/diff/6/1005#newcode3774
Line 3774: // Debugger message handler which counts then number of times it is
called.
On 2009/03/31 11:08:06, Mads Ager wrote:
> then -> the

Done.