RFR: 8288984: Simplification in Shutdown.exit [v2]

[Alan Bateman]

On Mon, 4 Jul 2022 01:59:37 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/Runtime.java line 89:
>> 
>>> 87:      * of the first invocation will be used; the status codes from other invocations
>>> 88:      * will be ignored. If this method is invoked from a shutdown hook the system
>>> 89:      * will deadlock.
>> 
>> Expressing this accurately is tricky - what is "first" here? I suggest the following:
>> 
>>> Invocations of this method are serialized such that only one invocation will actually proceed with the shutdown sequence and terminate the VM with the given status code. All other invocations will block indefinitely. If this method is invoked from a shutdown hook the system will deadlock.
>
> +1 - except for the "deadlock" part (see other comment).  I think the old paragraph is at least confusing, and perhaps even just wrong.  Let's say we've run `shutdown` so run all the hooks but not halted.  Then someone calls `exit(0)`.  That seems to suggest the call will block indefinitely, which is neither desirable nor what was actually implemented.

David's refinement looks good.  The sentence on deadlock is accurate as shutdown hooks run on other threads, not the thread calling System.ext.

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PR: https://git.openjdk.org/jdk/pull/9351