Home / Autodocs / exec.library
NAME
- AddTask
-
add a task to the system
SYNOPSIS
AddTask(task, initialPC, finalPC)
APTR AddTask(struct Task *, APTR, APTR);
A1 A2 A3
FUNCTION
Add a task to the system. A reschedule will be run; the task with the highest priority in the system will start to execute (this may or may not be the new task).
Certain fields of the task control block must be initialized and a stack allocated prior to calling this function. The absolute smallest stack that is allowable is something in the range of 100 bytes, but in general the stack size is dependent on what subsystems are called. In general 256 bytes is sufficient if only Exec is called, and 4K will do if anything in the system is called. DO NOT UNDERESTIMATE. If you use a stack sniffing utility, leave a healthy pad above the minimum value. The system guarantees that its stack operations will leave the stack longword aligned.
This function will temporarily use space from the new task's stack for the task's initial set of registers. This space is allocated starting at the SPREG location specified in the task control block (not from SPUPPER). This means that a task's stack may contain static data put there prior to its execution. This is useful for providing initialized global variables or some tasks may want to use this space for passing the task its initial arguments.
A task's initial registers are set to zero (except the PC).
The TC_MEMENTRY field of the task structure may be extended by the user to hold additional MemLists (as returned by AllocEntry()). These will be automatically be deallocated at RemTask() time. If the code you have used to start the task has already added something to the MEMENTRY list, simply use AddHead to add your new MemLists in. If no initialization has been done, a NewList will need to be performed.
Certain fields of the task control block must be initialized and a stack allocated prior to calling this function. The absolute smallest stack that is allowable is something in the range of 100 bytes, but in general the stack size is dependent on what subsystems are called. In general 256 bytes is sufficient if only Exec is called, and 4K will do if anything in the system is called. DO NOT UNDERESTIMATE. If you use a stack sniffing utility, leave a healthy pad above the minimum value. The system guarantees that its stack operations will leave the stack longword aligned.
This function will temporarily use space from the new task's stack for the task's initial set of registers. This space is allocated starting at the SPREG location specified in the task control block (not from SPUPPER). This means that a task's stack may contain static data put there prior to its execution. This is useful for providing initialized global variables or some tasks may want to use this space for passing the task its initial arguments.
A task's initial registers are set to zero (except the PC).
The TC_MEMENTRY field of the task structure may be extended by the user to hold additional MemLists (as returned by AllocEntry()). These will be automatically be deallocated at RemTask() time. If the code you have used to start the task has already added something to the MEMENTRY list, simply use AddHead to add your new MemLists in. If no initialization has been done, a NewList will need to be performed.
INPUTS
- task
-
pointer to the task control block (TCB). All unset fields must be zero.
- initialPC
-
the initial entry point's address
- finalPC
-
the finalization code entry point's address. If zero, the system will use a general finalizer. This pointer is placed on the stack as if it were the outermost return address.
RESULT
For V36, AddTask returns either a NULL or the address of the new task. Old code need not check this.
WARNING
Tasks are a low-level building block, and are generally unable to call dos.library functions, or any system function that might indirectly call dos.library. See the AmigaDOS CreateProc() and CreateNewProc() functions for information on Processes.