EAFP vs LBYL (was Re: A little disappointed so far)

[Robin Becker]

In article <mO1ya.115460$3M4.2627893 at news1.tin.it>, Alex Martelli
<aleax at aleax.it> writes
......
>So, if A's structure is:
>
>    if iswhatiwant(thefile):
>        useappropriately(thefile)
>    else:
>        dealwithwrongness()
>
>then A is buggy.  That is because, between the moment in which the test
>'iswhatiwant' runs (and returns a true value), and the later moment in
>which procedure 'useappropriately' runs, *just about anything may have
>happened* -- in particular, some other program Z might have removed or
>modified 'thefile' so that it's NOT what A wants any more.  I.e., A may
>lose control of the CPU between the moment it tests and the later time
>in which it uses the result of that test.
>
>This is known as a "race condition" and it's among the hardest problems
>you may run into.  A may seem to be running just fine 99 times and then
>the 100th time BOOM -- because of accidents of timing between A and
>other stuff that may be running "at the same time"... a "race", so to
>speak, whence the name whereby this horrid condition is known.

If race conditions are a problem shouldn't we be doing something like

while not havelockon(thefile):
        pass    # or sleep etc
useappropriately(thefile)
giveuplockon(thefile)

if we actually need to do something with/to thefile?

The real problem, for me at least, seems to be that concurrency is hard
no matter how you attempt to deal with it. I guess that race conditions
could apply to almost every file operation nowadays, but few people
program that way. Trying to deal with the race using try/except seems
harder than using an appropriate guard clause or busy loop.
-Whoops they migrated me to another processor-ly yrs- 
Robin Becker