Service Function 0005h Unhook Notification Chain

les di, CBInfo ;es:di points to SWCALLBACKINFO structure

mov ax, 0005h ;Unhook Notification Chain

call [Service] ;service-function handler

jc error_handler ;carry set on error

Unhook Notification Chain (Service Function 0005h) directs the task switcher to remove the specified SWCALLBACKINFO structure from its notification chain. Client programs that are on the notification chain must call this function when they terminate.

Parameter

CBInfo

Points to the client program's SWCALLBACKINFO structure. The SWCALLBACKINFO structure has the following form:

SWCALLBACKINFO STRUC

scbiNext dd ? ;address of next structure in chain

scbiEntryPoint dd ? ;address of notification-function handler

scbiReserved dd ? ;reserved

scbiAPI dd ? ;address of list of SWAPIINFO structures

SWCALLBACKINFO ENDS

For a full description of the SWCALLBACKINFO and SWAPIINFO structures, see Section 7.11, “Structures.”

Return Value

If the function is successful, the carry flag is clear and the AX register contains 0000h. If the task switcher does not support this function, the carry flag is set.

Comments

Whether a client program has used Build Notification Chain (Interrupt 2Fh Function 4B01h) or Hook Notification Chain (Service Function 0004h), it must call Unhook Notification Chain to remove itself from the notification chain of every task switcher to which it belongs.

A task switcher that rebuilds its notification chain at every session switch can return from Unhook Notification Chain with no other action.

A task switcher processing Unhook Notification Chain can enable interrupts and call any MS-DOS system function. Although the task switcher modifies the AX register, it must preserve all other registers.