Threads vs Processes

[Shitiz Bansal]

How do i share memory between processes?

"sjdevnull at yahoo.com" <sjdevnull at yahoo.com> wrote: John Henry wrote:
> If you're sharing things, I would thread. I would not want to  pay the
> expense of a process.

This is generally a false cost.  There are very few applications where
thread/process startup time is at all a fast path, and there are
likewise few where the difference in context switching time matters at
all.  Indeed, in a Python program on a multiprocessor system, process
are potentially faster than threads, not slower.

Moreover, to get at best a small performance gain you pay a huge cost
by sacrificing memory protection within the threaded process.

You can share things between processes, but you can't memory protect
things between threads.  So if you need some of each (some things
shared and others protected), processes are the clear choice.

Now, for a few applications threads make sense.  Usually that means
applications that have to share a great number of complex data
structures (and normally, making the choice for performance reasons
means your design is flawed and you could help performance greatly by
reworking it--though there may be some exceptions).  But the general
rule when choosing between them should be "use processes when you can,
and threads when you must".

Sadly, too many programmers greatly overuse threading.  That problem is
exacerbated by the number of beginner-level programming books that talk
about how to use threads without ever mentioning processes (and without
going into the design of multi-execution apps).

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