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Q29830: C 5.10 MTDYNA.DOC: Threads

Article: Q29830
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 15-JAN-1991

The following information is from "Section 1: Introduction" of the
Microsoft C version 5.10 MTDYNA.DOC file.

1.1   Threads

Three types of multitasking are present in OS/2: screen groups,
processes, and threads. A screen group, the highest-level multitasking
element, consists of one or more processes that share a logical screen
and keyboard. For example, a word processor and a database operating
simultaneously under OS/2 would represent two screen groups. A process
is the part of an executing program that is the unit of ownership for
resources such as memory, open files, and semaphores. Finally, a
thread is the execution path within a process, and it is the smallest
multitasking unit managed by OS/2. A process may consist of one or
more threads.

Two sample programs supplied with this release highlight the use of
threads. The first example program, mhello.c, is a multiple-thread
version of the classic "Hello world" program. The second example
program, snap.c, uses multiple threads to capture screen images to a
file.

A pictorial representation of screen groups, processes, and threads is
shown in Figure 1 below. Each screen group consists of two processes.
These processes are composed of several threads. In any process,
thread 1 is the main thread. All threads in a process are independent.

Figure 1. Screen Groups, Processes, and Threads

+============================================================================
|
|                                    OS/2
|
| +----------------------------------+  +----------------------------------+
| |          Screen Group 1          |  |          Screen Group 2          |
| | +------------+    +------------+ |  | +------------+    +------------+ |
| | |  Process 1 |    |  Process 2 | |  | |  Process 1 |    |  Process 2 | |
| | |            |    |            | |  | |            |    |            | |
| | | *Thread 1* |    |            | |  | | *Thread 1* |    |  *Thread 1*| |
| | |            |    | *Thread 1* | |  | | *Thread 2* |    |            | |
| | | *Thread 2* |    |            | |  | | *Thread 3* |    |  *Thread 2*| |
| | |            |    |            | |  | |            |    |            | |
| | +------------+    +------------+ |  | +------------+    +------------+ |
| |                                  |  |                                  |
| +----------------------------------+  +----------------------------------+
|
+============================================================================

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