GetPrimitiveArrayCritical should not be used

[bgilbert]

The JNI code uses GetPrimitiveArrayCritical() to get destination buffers for read_region() and read_associated_image(). This was presumably done to avoid an extra buffer copy, but the JNI documentation cautions that the *Critical methods should not be used for long-running operations.

[agoode]

In theory this should be fine. I don't see any rules we are breaking here with the critical methods. As far as I can see, the alternative is to use the NIO GetDirectBufferAddress which you could probably retrofit into things.