Re: [Boost-users] safe check if lockfree::queue is empty

Subject: Re: [Boost-users] safe check if lockfree::queue is empty
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2013-04-02 10:26:56

AMDG

On 04/02/2013 03:45 AM, niXman wrote:
> Hi,
> 
> I read the docs about lockfree::queue::empty() and understang what this way
> is not safe in multithreaded program.
> The question is, how can I verify that the queue is empty?

It's impossible.  The problem is that by the
time you use the answer, the state of the
queue may have changed.  You can't do better
than the built in empty.

> Will it be correct the following code?
> 

No.  It will re-order the elements if there is more than one.

> bool empty() {
>    T *tmp = 0;
>    if ( queue.pop(tmp) ) {
>       queue.push(tmp);
>       return false;
>    }
>    return true;
> }
> 

In Christ,
Steven Watanabe