Define and specify Runtime shutdown sequence

Summary

Update the java.lang.Runtime class specification to describe the shutdown sequence.

Problem

The shutdown hooks mechanism was added in JDK 1.3. This allowed some special "hooks" (really, threads) to be run after System.exit was called but before the JVM actually terminated. Unfortunately, documentation of the exact behavior of hooks with respect to the actual shutdown and exit of the JVM was piecemeal, and there were several places in the specifications that had misleading or out-of-date information, such as statements that "The System.exit() method terminates the JVM." Similarly out-of-date information was present in the JLS, the JVMS, and the JNI Specifications.

Solution

Update the java.lang.Runtime class specification to define the shutdown sequence, what causes it to start, and what happens when it finishes (or not). Also make minor adjustments to various places in Thread and System.

Note that corresponding changes to other specifications are also being made:

• JDK-8290388 - JVMS changes
• JDK-8290196 - JLS changes
• JDK-8290482 - JNI Specification changes

Specification

See attached specdiff.