Concurrency and Threads - Operating Systems: Principles and Practice - page 165

Logical View

Thread 1 Thread 2

while(1) f while(1) f

thread yield() thread yield()

g g

Physical Reality

Thread 1's instructions Thread 2's instructions Processor's instructions

call thread yield call thread yield

save state to stack save state to stack

save state to TCB save state to TCB

choose another thread choose another thread

load other thread state load other thread state

call thread yield call thread yield

save state to stack save state to stack

save state to TCB save state to TCB

choose another thread choose another thread

load other thread state load other thread state

return thread yield return thread yield

call thread yield call thread yield

save state to stack save state to stack

save state to TCB save state to TCB

choose another thread choose another thread

load other thread state load other thread state

return thread yield return thread yield

call thread yield call thread yield

save state to stack save state to stack

save state to TCB save state to TCB

choose another thread choose another thread

load other thread state load other thread state

return thread yield return thread yield

... ... ...

Figure4.13: Interleaving of instructions when two threads loop and call
threadyield() .

4.4.4 Multi-threaded processes

So far, we have described how to implement multiple threads in a kernel.
Threads are also a useful abstraction for applications, so modern operating
systems support multi-threaded processes.

We will describe how operating systems provide the abstraction of multi-
threaded processes in two

steps.

First, we will describe how single-threaded processes mesh with the mech-
anisms we've just described for implementing a multi-threaded operating
system.

Then, we will describe a few small additions needed to support multi-
threaded processes.