Allow opting out of catching unhandled C++ exceptions

Add a system option to control whether the main loop and threads are run
from within a try-catch block, or outside of it.

Traditionally, wxWidgets has caught all unhandled C++ exceptions
that are about to cause the program to be aborted.

For many situations this is probably a good thing, but the downside
is that it severely complicates debugging the source of such exceptions.
The backtrace will only show the stack since wx's exception handler,
but not where the exception occurred in the first place.

Any crashdumps created by the OS also suffer from the same issue;
backtraces are mostly useless in these cases.

The following classes with try-catch blocks do not obey the new system
option for now: wxDataViewRendererBase, wxDocTemplate, wxIDropTarget

Author: lanurmi

interface/wx/sysopt.h

@@ -37,6 +37,15 @@
         this option allows changing it without modifying the program code and
         also applies to asserts which may happen before the wxApp object
         creation or after its destruction.
+    @flag{catch-unhandled-exceptions}
+        If set to zero, wxWidgets will not catch unhandled exceptions, but
+        rather lets the default behavior of aborting the program take place.
+        Not catching unhandled exceptions makes debugging easier, as the
+        backtrace is more likely to show what actually happened, and where.
+        The same applies to any crash dumps generated due to unhandled exceptions.
+        By default unhandled exceptions are eventually caught by wxWidgets.
+        This flag should be set very early during program startup, within
+        the constructor of the wxApp derivative.
     @endFlagTable
 
     @section sysopt_win Windows

src/common/event.cpp

@@ -22,6 +22,7 @@
 #include "wx/event.h"
 #include "wx/eventfilter.h"
 #include "wx/evtloop.h"
+#include "wx/sysopt.h"
 
 #ifndef WX_PRECOMP
     #include "wx/list.h"
@@ -1666,6 +1667,10 @@ bool wxEvtHandler::TryHereOnly(wxEvent& event)
 
 bool wxEvtHandler::SafelyProcessEvent(wxEvent& event)
 {
+    if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+    {
+        return ProcessEvent(event);
+    }
 #if wxUSE_EXCEPTIONS
     try
     {

src/common/evtloopcmn.cpp

@@ -20,6 +20,7 @@
 
 #include "wx/scopeguard.h"
 #include "wx/apptrait.h"
+#include "wx/sysopt.h"
 #include "wx/private/eventloopsourcesmanager.h"
 
 // Counts currently existing event loops.
@@ -342,6 +343,11 @@ int wxEventLoopManual::DoRun()
     // wxModalEventLoop depends on this (so we can't just use ON_BLOCK_EXIT or
     // something similar here)
 #if wxUSE_EXCEPTIONS
+    if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+    {
+        Loop();
+        return m_exitcode;
+    }
     for ( ;; )
     {
         try

src/common/init.cpp

@@ -29,6 +29,7 @@
 #include "wx/atomic.h"
 
 #include "wx/except.h"
+#include "wx/sysopt.h"
 
 #if defined(__WINDOWS__)
     #include "wx/msw/private.h"
@@ -575,6 +576,10 @@ int wxEntryReal(int& argc, wxChar **argv)
         return wxApp::GetFatalErrorExitCode();
     }
 
+    if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+    {
+        return DoEntryReal();
+    }
     wxTRY
     {
         return DoEntryReal();

src/msw/thread.cpp

@@ -38,6 +38,7 @@
 
 #include "wx/except.h"
 #include "wx/dynlib.h"
+#include "wx/sysopt.h"
 
 // must have this symbol defined to get _beginthread/_endthread declarations
 #ifndef _MT
@@ -503,9 +504,13 @@ class wxThreadKeepAlive
 /* static */
 void wxThreadInternal::DoThreadOnExit(wxThread *thread)
 {
+    if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+    {
+        return thread->OnExit();
+    }
     wxTRY
     {
-        thread->OnExit();
+        return thread->OnExit();
     }
     wxCATCH_ALL( wxTheApp->OnUnhandledException(); )
 }
@@ -532,15 +537,17 @@ THREAD_RETVAL wxThreadInternal::DoThreadStart(wxThread *thread)
 {
     wxON_BLOCK_EXIT1(DoThreadOnExit, thread);
 
-    THREAD_RETVAL rc = THREAD_ERROR_EXIT;
-
+    if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+    {
+        return DoThreadStartWithoutExceptionHandling(thread);
+    }
     wxTRY
     {
-        rc = DoThreadStartWithoutExceptionHandling(thread);
+        return DoThreadStartWithoutExceptionHandling(thread);
     }
     wxCATCH_ALL( wxTheApp->OnUnhandledException(); )
 
-    return rc;
+    return THREAD_ERROR_EXIT;
 }
 
 /* static */

src/unix/threadpsx.cpp

@@ -27,6 +27,7 @@
 
 #include "wx/thread.h"
 #include "wx/except.h"
+#include "wx/sysopt.h"
 
 #ifndef WX_PRECOMP
     #include "wx/app.h"
@@ -889,6 +890,11 @@ void *wxThreadInternal::PthreadStart(wxThread *thread)
                    wxT("Thread %p about to enter its Entry()."),
                    THR_ID(pthread));
 
+        if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+        {
+            CallThreadEntryWithoutExceptionHandling(pthread, thread);
+        }
+        else
         wxTRY
         {
             CallThreadEntryWithoutExceptionHandling(pthread, thread);
@@ -1740,6 +1746,11 @@ void wxThread::Exit(ExitCode status)
     // might deadlock if, for example, it signals a condition in OnExit() (a
     // common case) while the main thread calls any of functions entering
     // m_critsect on us (almost all of them do)
+    if ( wxSystemOptions::IsFalse("catch-unhandled-exceptions") )
+    {
+        OnExit();
+    }
+    else
     wxTRY
     {
         OnExit();