Re: "This method blocks until..." means what exactly?

Nigel Wade <>
Fri, 30 Jul 2010 11:20:47 +0100
On 30/07/10 10:40, Arved Sandstrom wrote:

Esmond Pitt wrote:

On 29/07/2010 7:21 PM, Arved Sandstrom wrote:

A "blocking" function doesn't return until its work is completed.

But *all* functions have that characteristic (except for specifically
designated async functions that generally post results via callbacks).
It's just not a useful definition. You can't usefully regard 'still
running' or 'hasn't returned yet' as 'blocking'. 'Blocked' generally
means waiting for something *else*, e.g. in this case waiting for the
kernel or the network to deliver some data.

As general as it may be, it's actually still a useful definition,
because we invariably use it only for those functions where there can be
a significant delay before the work associated with the function
completes. You _could_ use the term for a function that adds two
integers, but nobody would bother, it serves no purpose.

So the way you phrased it in your last sentence is usually *when* and
*where* we tend to use this general definition. It doesn't change the
fact that it's a general definition.


I infer "blocking" to imply:

 a) no useful work is being performed
 b) the duration is indeterminate (usually due to external factors)

whether it yields the CPU to other threads, or spins, isn't material to
the meaning of "blocked" - it may do either.

Nigel Wade

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