GC Handles
Synopsys
	
	
	GC handles are wrappers that are used to keep references to
	managed objects in the unmanaged space and preventing the
	object from being disposed.
	
	
These are the C equivalents of the 
System.GCHandle
	structure.
	
There are two kinds of GCHandles that can be created:
	
	To retrieve the target address of an object pointed to by a
	
GCHandle you should use
	
mono_gchandle_get_target.
	
For example, consider the following C code:
static MonoObject* o = NULL;
	The object in `o' will *NOT* be scanned.
	
If you need to store an object in a C variable and prevent
	it from being collected, you need to acquire a GC handle for
	it.
guint32 handle = mono_gchandle_new (my_object, TRUE);
	TRUE means the object will be pinned, so it won't move in
	memory when we'll use a moving GC. You can access the
	MonoObject* referenced by a handle with:
MonoObject* obj = mono_gchandle_get_target (handle);
	When you don't need the handle anymore you need to call:
mono_gchandle_free (handle);
	Note that if you assign a new object to the C var, you need
	to get a new handle, it's not enough to store a new object in
	the C var.
	
So code that looked like this:
static MonoObject* obj = NULL;
...
obj = mono_object_new (...);
// use obj
...
// when done to allow the GC to collect obj
obj = NULL;
	should now be changed to:
static guint32 o_handle;
...
MonoObject *obj = mono_object_new (...);
o_handle = mono_gchandle_new (obj, TRUE);
// use o or mono_gchandle_get_target (o_handle) 
...
// when done to allow the GC to collect obj
mono_gchandle_free (o_handle);
		
    mono_gchandle_new
    
        
        
            
            Syntax
            guint32
mono_gchandle_new (MonoObject *obj, gboolean pinned)
            
            Parameters
            | obj | managed object to get a handle for | 
| pinned | whether the object should be pinned | 
             Return value
             	 a handle that can be used to access the object from unmanaged code.
             Description
             
 This returns a handle that wraps the object, this is used to keep a
 reference to a managed object from the unmanaged world and preventing the
 object from being disposed.
 If 
pinned is false the address of the object can not be obtained, if it is
 true the address of the object can be obtained.  This will also pin the
 object so it will not be possible by a moving garbage collector to move the
 object. 
 
     
  
    mono_gchandle_new_weakref
    
        
        
            
            Syntax
            guint32
mono_gchandle_new_weakref (GCObject *obj, gboolean track_resurrection)
            
            Parameters
            | obj | managed object to get a handle for | 
| track_resurrection | Determines how long to track the object, if this is set to TRUE, the object is tracked after finalization, ifFALSE, the object is only tracked up until the point of finalization. | 
             Return value
             	 a handle that can be used to access the object from
	 unmanaged code.
             Description
             
 This returns a weak handle that wraps the object, this is used to
 keep a reference to a managed object from the unmanaged world.
 Unlike the 
mono_gchandle_new the object can be reclaimed by the
 garbage collector.  In this case the value of the GCHandle will be
 set to zero.
 If 
track_resurrection is 
TRUE the object will be tracked through
 finalization and if the object is resurrected during the execution
 of the finalizer, then the returned weakref will continue to hold
 a reference to the object.   If 
track_resurrection is 
FALSE, then
 the weak reference's target will become 
NULL as soon as the object
 is passed on to the finalizer.
 
         
     
  
    mono_gchandle_get_target
    
        
        
            
            Syntax
            MonoObject*
mono_gchandle_get_target (guint32 gchandle)
            
            Parameters
            | gchandle | a GCHandle's handle. | 
             Return value
             	 a pointer to the MonoObject* represented by the handle or
	 NULL for a collected object if using a weakref handle.
             Description
             
 The handle was previously created by calling 
mono_gchandle_new or
 
mono_gchandle_new_weakref.