Make catching of exceptions from Fibers optional

This commit allows exceptions from Fibers to be completely uncaught thus
causing a termination of the program and, depending on the configuration,
creation of a core dump.

An attached debugger can then be used to properly investigate the status of the
program at the time of the failure.

Author: Marenz

src/core/thread.d

@@ -3445,14 +3445,16 @@ private
         obj.m_ctxt.tstack = obj.m_ctxt.bstack;
         obj.m_state = Fiber.State.EXEC;
 
-        try
+        if( obj.catch_exceptions ) try
         {
             obj.run();
         }
         catch( Throwable t )
         {
             obj.m_unhandled = t;
         }
+        else
+            obj.run();
 
         static if( __traits( compiles, ucontext_t ) )
           obj.m_ucur = &obj.m_utxt;
@@ -3864,18 +3866,20 @@ class Fiber
      * Params:
      *  fn = The fiber function.
      *  sz = The stack size for this fiber.
+     *  ce = If true, exceptions will be caught and assigned to m_unhandled
      *
      * In:
      *  fn must not be null.
      */
-    this( void function() fn, size_t sz = PAGESIZE*4 ) nothrow
+    this( void function() fn, size_t sz = PAGESIZE*4, bool ce = true ) nothrow
     in
     {
         assert( fn );
     }
     body
     {
         allocStack( sz );
+        catch_exceptions = ce;
         reset( fn );
     }
 
@@ -3887,18 +3891,20 @@ class Fiber
      * Params:
      *  dg = The fiber function.
      *  sz = The stack size for this fiber.
+     *  ce = If true, exceptions will be caught and assigned to m_unhandled
      *
      * In:
      *  dg must not be null.
      */
-    this( void delegate() dg, size_t sz = PAGESIZE*4 ) nothrow
+    this( void delegate() dg, size_t sz = PAGESIZE*4, bool ce = true ) nothrow
     in
     {
         assert( dg );
     }
     body
     {
         allocStack( sz );
+        catch_exceptions = ce;
         reset( dg );
     }
 
@@ -4017,7 +4023,7 @@ class Fiber
      * fibers that have terminated, as doing otherwise could result in
      * scope-dependent functionality that is not executed.
      * Stack-based classes, for example, may not be cleaned up
-     * properly if a fiber is reset before it has terminated. 
+     * properly if a fiber is reset before it has terminated.
      *
      * In:
      *  This fiber must be in state TERM or HOLD.
@@ -4173,6 +4179,13 @@ class Fiber
         }
     }
 
+    //
+    // If true, exceptions thrown inside the fiber will be caught and assigned
+    // to m_unhandled, otherwise exceptions will cause a termination of the
+    // program
+    //
+    bool catch_exceptions;
+
 private:
     //
     // Initializes a fiber object which has no associated executable function.