--- a/MessageTracer.st	Sun Sep 08 16:43:18 2019 +0200
+++ b/MessageTracer.st	Sun Sep 15 11:13:23 2019 +0200
@@ -1,3 +1,5 @@
+"{ Encoding: utf8 }"
+
 "
  COPYRIGHT (c) 1994 by Claus Gittinger
 	      All Rights Reserved
@@ -790,6 +792,39 @@
     "Modified: 22.10.1996 / 17:40:06 / cg"
 !
 
+trapMethod:aMethod inProcess:aProcess withChildProcesses:withChildProcessesBoolean
+    "arrange for the debugger to be entered when aMethod is about to be executed,
+     but only, if executed by aProcess or one of aProcess's offspring.
+     This allows for breakpoints to be set on system-critical code.
+     The trap will only fire for selected processes (making browsers etc. still usable).
+     Use unwrapMethod or untrapClass to remove this trap.
+     Be careful, to not place a trap on code needed in the debugger (i.e. on scrollBars etc.);
+     if there is a need to trap those, use the low-level wrap-methods, and put a check into the
+     entry/leave blocks."
+
+    |pid|
+
+    pid := aProcess id. "/ fetch here, so the child detection works even when aProcess has died
+    ^ self wrapMethod:aMethod
+              onEntry:[:con |
+                        |active shouldBreak|
+
+                        active := Processor activeProcess.
+                        withChildProcessesBoolean ifTrue:[
+                            shouldBreak := (active processGroupId = pid) or:[ active creatorId = pid]    
+                        ] ifFalse:[
+                            shouldBreak := active processGroupId = pid.
+                        ].
+                        shouldBreak ifTrue:[
+                            BreakpointSignal raiseRequestWith:nil errorString:nil in:con
+                        ]
+                      ]
+               onExit:LeaveBreakBlock.
+
+    "Created: 14.10.1996 / 15:38:46 / cg"
+    "Modified: 22.10.1996 / 17:40:06 / cg"
+!
+
 trapMethod:aMethod onReturnIf:conditionBlock
     "arrange for the debugger to be entered when aMethod returns
      and conditionBlock evaluates to true.