using ReadWriteLocks

# The type provided by this package is ReadWriteLock.
# It has a single constructor.
rwlock = ReadWriteLock()

# This lock provides access to a read lock and a write lock
rlock = read_lock(rwlock)
wlock = write_lock(rwlock)

# To acquire a read lock:
lock!(rlock)

# To release a read lock:
unlock!(rlock)

#=
Write locks provide the same interface.

You can acquire any number of read locks at a time.
A read lock will block if a write lock has been acquired.
A write lock will block if a read lock or write lock has been acquired.
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