INT 2F C - 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(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running. Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes. SeeAlso: AX=160Bh,AX=4B02h Format of task switcher callback info structure: Offset Size Description (Table 02817) 00h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. pointer to next callback info structure 04h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. pointer to notification function (see #02818) 08h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. reserved 0Ch DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. address of zero-terminated list of API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running. Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes. 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