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Python proc vs thread

In python - what is the difference between a process, a child process (that has been forked), the output of a fork-exec and a thread? Actually I get the difference between the first two - (I think) that when forking you wind up with a new process that is a virtual copy of an existing parent process only running separately with a new PID. But I lost the trail when they got into fork-exec and then the thread concept.

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gelonida

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amigan_99

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Thank you very much! A point of clarification - if you have a moment - can you explain "not all modifications to Python variables are atomic"? I think of atomic from Democratis as a small indivisible particle. Not sure how that applies to a Python variable.

gelonida

OK: atomic operation in computer science means something like
"non interruptable by another thread." so an atomic operation would either not be executed or it wouild be completely executed.
Under no circujmstance it would be possible, that another thread interrupts an atomic operation while 'half'of the work is done.

you can refer to http://en.wikipedia.org/wiki/Atomic_operation

By the way it seems, that my above statement is wrong. some googling seems to indicate, that Python variable assignments are atomic operations.

However commands like
a += 1
a, b = b, a

would not be and modifying several members of an object wouldn't thus normally
Locks should be used in order to avoid, that an object is in an inconsistent state before being accessed by another thread.

amigan_99

ASKER

Thank you again very much.