Examples of com.sleepycat.je.log.FileManager.lockEnvironment()

• com.sleepycat.je.log.FileManager.lockEnvironment()
  Lock the environment. Return true if the lock was acquired. If exclusive is false, then this implements a single writer, multiple reader lock. If exclusive is true, then implement an exclusive lock. There is a lock file and there are two regions of the lock file: byte 0, and byte 1. Byte 0 is the exclusive writer process area of the lock file. If an environment is opened for write, then it attempts to take an exclusive write lock on byte 0. Byte 1 is the shared reader process area of the lock file. If an environment is opened for read-only, then it attempts to take a shared lock on byte 1. This is how we implement single writer, multi reader semantics. The cleaner, each time it is invoked, attempts to take an exclusive lock on byte 1. The owning process already either has an exclusive lock on byte 0, or a shared lock on byte 1. This will necessarily conflict with any shared locks on byte 1, even if it's in the same process and there are no other holders of that shared lock. So if there is only one read-only process, it will have byte 1 for shared access, and the cleaner can not run in it because it will attempt to get an exclusive lock on byte 1 (which is already locked for shared access by itself). If a write process comes along and tries to run the cleaner, it will attempt to get an exclusive lock on byte 1. If there are no other reader processes (with shared locks on byte 1), and no other writers (which are running cleaners on with exclusive locks on byte 1), then the cleaner will run.