Aufgabe 5: Zeitscheiben

Constructor Initializes the context using prepareContext with the highest aligned address of the reserved_stack_space array as stack pointer (top of stack).

Note

Remember: Stacks grow to the lower addresses on x86!

Function to start a thread.

For the first activation of a thread, we need a "return address" pointing to a function that will take care of calling C++ virtual methods. For this purpose, we use this kickoff() function.

Activating kickoff

The thread initialization via prepareContext() not only initializes the Stack for the first thread change, but also pushes the address of kickoff() as return address to the stack. Consequently, the first execution of context_switch() will start execution by returning to the beginning of kickoff() .

This kickoff() function simply calls the action() method on the thread passed as parameter and, thus, resolves the virtual C++ method.

Note

As this function is never actually called, but only executed by returning from the threads's initial stack, it may never return. Otherwise garbage values from the stack will be interpreted as return address and the system might crash.

Parameters

object

Thread to be started

Activates the first thread on this CPU.

Calling the method starts the first thread on the calling CPU. From then on, Thread::resume() must be used all subsequent context switches.

Switches from the currently running thread to the next one.

The values currently present in the non-scratch (callee-saved) registers will be stored on this thread's stack; the corresponding values belonging to next thread will be loaded (from next's stack).

Parameters

next	Pointer to the next thread.

Method that contains the thread's program code.

Derived classes are meant to override this method to provide meaningful code to be run in this thread.

Implemented in Application, and KeyboardApplication.