review request: 4244896: (process) Provide System.getPid(), System.killProcess(String pid) (original) (raw)

David Holmes david.holmes at oracle.com
Fri Jun 1 01:06:04 UTC 2012

Jeff,

On 1/06/2012 10:19 AM, Jeff Hain wrote:

Hi.

185 public boolean waitFor(long timeout, TimeUnit unit) 186 throws InterruptedException { 187 long now = System.nanoTime(); 188 189 long end = now + 190 (timeout<= 0 ? 0 : TimeUnit.NANOSECONDS.convert(timeout, unit));_ _191_ _192 if (end<= 0) // overflow_ _193 end = Long.MAXVALUE;_ _194_ _195 long rem = end - now;_ _196 do {_ _197 try {_ _198 exitValue();_ _199 return true;_ _200 } catch(IllegalThreadStateException ex) {_ _201 if(rem> 0) 202 Thread.sleep( 203 Math.min(TimeUnit.NANOSECONDS.toMillis(rem) + 1, 100)); 204 } 205 rem = end - System.nanoTime(); 206 } while(rem> 0); 207 return false; 208 }

If System.nanoTime() is close to wrapping, this code would consider overflow even for a not-so-large timeout,

If System.nanoTime is close to wrapping then we have all sorts of problems to worry about. But you are right. The way to handle this with no overflow issues is to track the elapsed time (System.nanoTime() - start) which will always give a positive result when less than 2^63 nanoseconds elapse. That then gets subtracted from the requested timeout to give the rem value.

and the wait could stop earlier than expected. (Also "now" should rather be called "startTime" or so (since at some point it's no longer current time).)

One could do as in ScheduledThreadPoolExecutor, and use an offset on System.nanoTime().

Aside: I don't see that in latest version of STPE.

Cheers, David

Or, just remove lines 192-194 : it's not really a problem if "end" wraps, since it should unwrap when doing "end - System.nanoTime()" (supposing we don't spend centuries in the method).

Or, only work with delta (also supposing we don't wait for centuries), never explicitly considering an "end" value, like this: public boolean waitFor(long timeout, TimeUnit unit) throws InterruptedException { final long startNS = System.nanoTime(); final long timeoutNS = (timeout<= 0 ? 0 : unit.toNanos(timeout));_ _long remNS = timeoutNS;_ _do {_ _try {_ _exitValue();_ _return true;_ _} catch(IllegalThreadStateException ex) {_ _if(remNS> 0) Thread.sleep( Math.min(TimeUnit.NANOSECONDS.toMillis(remNS) + 1, 100)); } remNS = timeoutNS - (System.nanoTime() - startNS); } while(remNS> 0); return false; } -Jeff

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