Int 2F/AX=4B01h

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DOS 5+ TASK SWITCHER - BUILD CALLOUT CHAIN

AX = 4B01h
CX:DX -> task switcher entry point (see #02819)
ES:BX = 0000h:0000h

Return:
ES:BX -> callback info structure (see #02817) or 0000h:0000h

Notes: Called by the task switcher. This function is hooked by clients which require notification of task switcher activities; the call must first be passed on to the prior handler with registers unchanged using a simulated interrupt. On return, the client must build a callback info structure and store the returned ES:BX in the "next" field, then return the address of its own callback info structure.. A client program must add itself to the notification chain if it provides services to other programs; before terminating, it must remove itself from the chain by calling the task switcher's entry point with AX=0005h (see #02819). The task switcher entry point should not be saved, as it is subject to change and will be provided on any notification call. The Windows 3.1 Standard Mode supports this API

See Also: AX=160Bh - AX=4B02h

Format of task switcher callback info structure: Offset Size Description (Table 02817) 00h DWORD pointer to next callback info structure 04h DWORD pointer to notification function (see #02818) 08h DWORD reserved 0Ch DWORD address of zero-terminated list of API info structures (see #02821)

(Table 02818) Values task switcher notification function is called with:. AX = function 0000h switcher initialization

Return:
AX = status 0000h if OK to load nonzero to abort task switcher 0001h query suspend BX = session ID

Return:
AX = status 0000h if OK to switch session 0001h if not 0002h suspend session BX = session ID interrupts disabled

Return:
AX = 0000h if OK to switch session = 0001h if not 0003h activate session BX = session ID CX = session status flags

bit 0:
Set if first activation of session

bits 1-15:
Reserved (0) interrupts disabled

Return:
AX = 0000h 0004h session active BX = session ID CX = session status flags

bit 0:
Set if first activation of session

bits 1-15:
Reserved (0)

Return:
AX = 0000h 0005h create session BX = session ID

Return:
AX = 0000h if OK to create session = 0001h if not 0006h destroy session BX = session ID

Return:
AX = 0000h 0007h switcher termination BX = flags

bit 0:
Set if calling switcher is only switcher loaded

bits 1-15:
Reserved (0)

Return:
AX = 0000h. ES:DI -> task switcher entry point (see #02819)

Notes: Function 0000h is generally called by the program which controls or invokes the task switcher, rather than by the task switcher itself; the entry point supplied to this function is not necessarily the entry point to the task switcher itself, and may be 0000h:0000h. If any client indicates that loading is not possible, all clients will be called with function 0007h; thus it is possible for a client to receive a termination notice without a corresponding initialization notice.. Except for functions 0002h and 0003h, the notification handler is called with interrupts enabled and may make any INT 21h function call; interrupts must not be enabled in functions 0002h and 0003h. Function 0007h may be called with ES:DI = 0000h:0000h if the entry point is no longer valid

Category: DOS-Based Task Switchers/Multitaskers - Int 2Fh - D

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