in reply to
Learning to use the hash effectively
Two things I will recommend:
- File locking. You have a very big race condition in your code:
you read in the contents of the file, alter them, then write them
back out. Between the time that you've read the file and you
write the file, someone else (ie. another process) could have
changed that file. Then you would overwrite that chance when
you write the file w/ your file contents.
One way to fix this is to open the file in read/append mode, flock
it, seek to the beginning of the file, read from it, alter the file
contents in memory, seek back to the beginning, truncate it, then
rewrite the contents from memory. The flock will prevent the
race condition (at least w/ another version of your program that
Another way to fix the problem is to use a semaphore file, like
in tilly's Simple Locking. Here, you flock a semaphore file when
you want to enter the "critical section" of your program, and
then other processes of your program cannot enter that critical
section until you have released the lock.
I would recommend the second approach.
- My second suggestion is, you could just use a DBM file for
this, particularly since you already have the notion of keys
mapping to values. In particular, you could use MLDBM to
serialize the data structure into the DBM format of your choice.