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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 138
SEC. 2.2
THREADS
107
a few of the major ones to give an idea of how it works. The calls we will describe
below are listed in Fig. 2-14.
Thread call
Description
Pthread
create
Create a new thread
Pthread
exit
Terminate the calling thread
Pthread
join
Wait for a specific thread to exit
Pthread
yield
Release the CPU to let another thread run
Pthread
attr
init
Create and initialize a thread’s attribute structure
Pthread
attr
destroy
Remove a thread’s attribute structure
Figure 2-14.
Some of the Pthreads function calls.
All Pthreads threads have certain properties. Each one has an identifier, a set of
registers (including the program counter), and a set of attributes, which are stored
in a structure. The attributes include the stack size, scheduling parameters, and
other items needed to use the thread.
A new thread is created using the
pthread
create
call. The thread identifier of
the newly created thread is returned as the function value. This call is intentionally
very much like the
fork
system call (except with parameters), with the thread iden-
tifier playing the role of the PID, mostly for identifying threads referenced in other
calls.
When a thread has finished the work it has been assigned, it can terminate by
calling
pthread
exit
.
This call stops the thread and releases its stack.
Often a thread needs to wait for another thread to finish its work and exit be-
fore continuing. The thread that is waiting calls
pthread
join
to wait for a specific
other thread to terminate. The thread identifier of the thread to wait for is given as
a parameter.
Sometimes it happens that a thread is not logically blocked, but feels that it has
run long enough and wants to give another thread a chance to run.
It can accom-
plish this goal by calling
pthread
yield
.
There is no such call for processes be-
cause the assumption there is that processes are fiercely competitive and each
wants all the CPU time it can get. However, since the threads of a process are
working together and their code is invariably written by the same programmer,
sometimes the programmer wants them to give each other another chance.
The next two thread calls deal with attributes.
Pthread
attr
init
creates the
attribute structure associated with a thread and initializes it to the default values.
These values (such as the priority) can be changed by manipulating fields in the
attribute structure.
Finally,
pthread
attr
destroy
removes a thread’s attribute structure, freeing up
its memory.
It does not affect threads using it; they continue to exist.
To get a better feel for how Pthreads works, consider the simple example of
Fig. 2-15.
Here the main program loops
NUMBER
OF
THREADS
times, creating
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