Backport of JSR 166

Dawid Kurzyniec's backport of JSR 166

<dependency>
    <groupId>backport-util-concurrent</groupId>
    <artifactId>backport-util-concurrent</artifactId>
    <version>3.1</version>
</dependency>

compile group: 'backport-util-concurrent', name: 'backport-util-concurrent', version: '3.1'

compile 'backport-util-concurrent:backport-util-concurrent:3.1'

libraryDependencies += "backport-util-concurrent" % "backport-util-concurrent" % "3.1"

<dependency org="backport-util-concurrent" name="backport-util-concurrent" rev="3.1"/>

@Grapes(
            @Grab(group='backport-util-concurrent', module='backport-util-concurrent', version='3.1')
        )

[backport-util-concurrent/backport-util-concurrent "3.1"]

'backport-util-concurrent:backport-util-concurrent:jar:3.1'