Make Time.now monotonically increasing
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Key: JRUBY-2788
URL: http://jira.codehaus.org/browse/JRUBY-2788
Project: JRuby
Issue Type: Improvement
Affects Versions: JRuby 1.1RC3
Environment: Linux
Reporter: Wayne Meissner
Assignee: Vladimir Sizikov
Priority: Minor
Attachments: Main.java
Related to JRUBY-2698, on some operating systems (e.g. linux),
System.nanoTime() is not monotonically increasing.
i.e. with two successive calls to System.nanoTime(), the second call can return
a value less than the first call.
This makes Time.now run backwards, which people assume should not happen.
Although its not a valid assumption, especially on multi-cpu machines, people
write code with that assumption, and jruby can break their code.
The attached code snippet demonstrates one possible workaround - it stores the
last time retrieved, and only returns the new value from System.nanoTime() if
it is greater than the stored value.
It has a couple of downsides, namely its more complex, and with multiple
threads calling it, it will hammer the memory bus as it updates the global
variable.
It needs someone else to verify that MonoTime.nanoTime() is indeed correct
under all circumstances.
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