DCE for the HP e3000 (B3821-90003)

26 Chapter3
Threads Architecture on MPE/iX
Threads Architecture
Threads Architecture
This section describes the architecture of threads on MPE/iX.
The following terminology is adopted throughout the remainder of this
document. The term process refers to the MPE/iX operating system
notion of process. The term task is defined as a multi-threaded
application (depending on the implementation, a task can consist of a
single process or multiple processes).
Threads on MPE/iX
A multi-threaded task on MPE/iX is implemented with multiple
processes (one per thread). A task’s threads are a cooperative processes
in that they share some resources that are normally private to a
process. All threads within a task share the same SR 5 space as the
initial thread (a process created using run or createprocess). The heap
and global variables are shared by all threads, along with loader
information and system information regarding open files and sockets.
All other process resources are private to the thread. Each thread has
its own NM stack, CM stack, pin number, PIB, PIBX, TCB, PCB, PCBX,
process port, and so on. Fields within these data structures that are
shared among threads (such as, file system information) are kept in a
common location.
Process Management and Threads
An initial thread is a process created using run or createprocess (or
fork and exec for POSIX). The threads of a task cannot exist
independently of the initial thread. If the initial thread terminates or is
killed, all of the task’s threads are terminated. A secondary thread
cannot be adopted by another task.
Each thread begins execution at an entry point specified at creation
time. The entry point is an MPE/iX procedure with one parameter. This
procedure resides in either the program file or the linked libraries of
the task.
When a thread is created, the following attributes can be specified:
Stack size: NM stack size for the thread
Inherit scheduling: inherit the scheduling policies of the
creating thread
Priority: priority of the thread
Scheduling policy: round robin, FIFO,...
Scheduling scope: priority is global/local