Did I misunderstand the concept of threads?

[Lars Uffmann]

Hey everyone!

In a previous post, I was asking about thread programming in C++ and was
pointed to the boost libraries. However, now I am reading in the
boost.thread documentation at
http://www.boost.org/doc/html/thread.html#thread.glossary / Table 15.26
for Thread State that "Running" means: "Currently executing on a
processor. Zero or more threads may be running at any time, with a
maximum equal to the number of processors."

So does that mean multithreading is only intended for multi-processor
environments? What I was thinking about was actually more like... handle
network data in a procedure (which I thought would be a thread) that is
permanently listening to incoming packets, while the rest of my
application (GUI) is still reacting to user input.

I have used a "thread" implementation of widestudio for this
successfully, so I didn't really have the idea this could be the wrong
approach.

What would be the correct approach to run several processes in parallel
on a single-core system (or regardless of the amount of cores)?

TIA,

Lars

 

[Matthias Buelow]

So does that mean multithreading is only intended for multi-processor
environments?

It just says that "Running" means the thread is currently being executed
on a CPU, not that the thread is runnable in general (as opposed to
waiting, sleeping, etc.) Obviously, you can't have more threads being
executed simultaneously than you have CPUs (cores). It's a bit silly
this trivial fact is mentioned explicitly.

 

[Pete Becker]

In a previous post, I was asking about thread programming in C++ and
was pointed to the boost libraries. However, now I am reading in the
boost.thread documentation at
http://www.boost.org/doc/html/thread.html#thread.glossary / Table 15.26
for Thread State that "Running" means: "Currently executing on a
processor. Zero or more threads may be running at any time, with a
maximum equal to the number of processors."

Yup. That's simply a physical fact: with only one processor, only one
thread of execution can run at a time.

So does that mean multithreading is only intended for multi-processor
environments?

No. On single-processor systems, the threading mechanism switches the
processor from one thread to another, giving each running thread a
chunk of run time. In fact, the same thing happens whenever there are
more threads than there are processors.

 

[Lars Uffmann]

Thank you Matthias & Pete for clearing that up I'm reading my way
through the boost.thread documentation as I'm writing this...

Best Regards,

Lars