MSHLFLAGS - OLE Programmer's Reference

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MSHLFLAGS

The MSHLFLAGS enumeration constants determine why the marshaling is to be done. These flags are used in the IMarshal interface and the CoMarshalInterface and CoGetStandardMarshal API functions.

MSHFLAGS is defined in WTYPES.IDL.

typedef enum tagMSHLFLAGS
{
MSHLFLAGS_NORMAL = 0,
MSHLFLAGS_TABLESTRONG = 1,
MSHLFLAGS_TABLEWEAK = 2
} MSHLFLAGS;

Elements
MSHLFLAGS_NORMAL

The marshaling is occurring because an interface pointer is being passed from one process to another. This is the normal case. The data packet produced by the marshaling process will be unmarshaled in the destination process. The marshaled data packet can be unmarshaled just once, or not at all. If the receiver unmarshals the data packet successfully, the CoReleaseMarshalData API function is automatically called on the data packet as part of the unmarshaling process. If the receiver does not or cannot unmarshal the data packet, the sender must call the CoReleaseMarshalData API function on the data packet.

MSHLFLAGS_TABLESTRONG

The marshaling is occurring because the data packet is to be stored in a globally-accessible table from which it can be unmarshaled one or more times, or not at all. The presence of the data packet in the table counts as a strong reference to the interface being marshaled, meaning that it is sufficient to keep the object alive. When the data packet is removed from the table, the table implementor must call the CoReleaseMarshalData API function on the data packet.

MSHLFLAGS_TABLESTRONG is used by the RegisterDragDrop API function when registering a window as a drop target. This keeps the window registered as a drop target no matter how many times the end-user drags across the window. The RevokeDragDrop API function calls CoReleaseMarshalData.

MSHLFLAGS_TABLEWEAK

The marshaling is occurring because the data packet is to be stored in a globally-accessible table from which it can be unmarshaled one or more times, or not at all. However, the presence of the data packet in the table acts as a weak reference to the interface being marshaled, meaning that it is not sufficient to keep the object alive. When the data packet is removed from the table, the table implementor must call the CoReleaseMarshalData API function on the data packet.

MSHLFLAGS_TABLEWEAK is typically used when registering an object in the Running Object Table (ROT). This prevents the object's entry in the ROT from keeping the object alive in the absence of any other connections. See IRunningObjectTable::Register for more information.

See Also
CoGetStandardMarshal, CoMarshalInterface, IMarshal

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