417
Subj : Re: recursive mutexes
To   : comp.programming.threads,comp.unix.programmer
From : David Schwartz
Date : Sun May 15 2005 12:56 pm


"Uenal Mutlu" <520001085531-0001@t-online.de> wrote in message 
news:d67fm3$hah$00$1@news.t-online.com...

> Recursive locking has less dangers than locking without recursive feature.
> Proof: using recursive locking you never can block or deadlock yourself,
> but using a locking method without recursive feature you can very easily 
> deadlock
> yourself.
> In the latter case even just blocking (ie. waiting for the lock) means 
> deadlock!
> Don't you see that?

    Okay, suppose I write a function that supposed to only be called if X is 
not locked. Calling it with X locked is a *bug*. Now suppose I  make a 
mistake -- I am only human. I call the function by mistake with X locked. 
The function goes to lock X itself. I *want* this to break because it 
indicates a *bug*. It is *bad* if this just magically works because then the 
bug will not get discovered.

    DS

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