Re: calling wait outside of loop

Thomas Hawtin <>
Sun, 07 May 2006 10:48:35 +0100
puzzlecracker wrote:

The argument is that calling wait prior to loop me cause a thread never
to be aweken (given that notify[all] has been called prior)

How does waiting in the loop prevent that:

 while(a condition){

and notify has been called prior to wait, indefinite sleep is

 what is the argument for calleding after the loop.

Are you asking why the following code is not used?

     if (...condition...) { // Wrong...

Firstly there is the problem of spurious wakeups. wait can exit at any
time, without reason. Therefore the loop is always necessary.

Even if there were no spurious wakeups, it's still usually wrong.
Typically you may have multiple threads waiting, only one of which can
proceed. Each thread will need to check the notify is for them. For
instance, two threads are waiting to take an element off a blocking
queue, if notifyAll is used both will wake but only one should grab the
new element.

Tom Hawtin
Unemployed English Java programmer

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