RFR: 8263903: Use Cleaner instead of finalize to auto stop Timer thread

[David Holmes]

On Sun, 21 Mar 2021 03:53:24 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to java.util.Timer, replacing the use of deprecated finalization-based cleanup with use of java.lang.ref.Cleaner.
> 
> In addition, Timer.cancel now cancels any later execution of the the no longer relevant cleanup.
> 
> Testing:
> mach5 tier1
> New AutoStop test verifies the specified cleanup behavior.
> (There are existing tests involving Timer.cancel.)

test/jdk/java/util/Timer/AutoStop.java line 47:

> 45:                 public void run() {
> 46:                     tdThread = Thread.currentThread();
> 47:                     synchronized(wakeup) {

tdThread should be set inside the sync block, and then doesn't need to be declared volatile

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PR: https://git.openjdk.java.net/jdk/pull/3106