file write collision consideration

[MRAB]

RGK wrote:
> I have a thread that is off reading things some of which will get 
> written into a file while another UI thread manages input from a user.
> 
> The reader-thread and the UI-thread will both want to write stuff to the 
> same output file. What first comes to mind is that there may be write 
> collisions, ie both trying to write at the same time.
> 
> Should I do something like:
> 
> 
> if busyFlag:
>   while busyFlag:
>      sleep(10)
> else:
>   busyFlag = True
>   {write stuff to file}
>   busyFlag = False
> 
> 
> in both threads?   Is there some other approach that would be more 
> appropriate?
> 
> Thanks in advance for your advice
> 
If you're using the threading module, I suggest you look at the 
threading.RLock class:

my_lock = threading.RLock()
...
with my_lock:
     {write stuff to file}

or, if you're using an older version of Python:

my_lock = threading.RLock()
...
my_lock.acquire()
{write stuff to file}
my_lock.release()