Locks a mutex resource. The output is the lock. So long as the lock tensor

is alive, any other request to use MutexLock with this mutex will wait.

This is particularly useful for creating a critical section when used in conjunction with MutexLockIdentity:

mutex = mutex_v2(
  shared_name=handle_name, container=container, name=name)

def execute_in_critical_section(fn, *args, **kwargs):
  lock = gen_resource_variable_ops.mutex_lock(mutex)

  with ops.control_dependencies([lock]):
    r = fn(*args, **kwargs)

  with ops.control_dependencies(nest.flatten(r)):
    with ops.colocate_with(mutex):
      ensure_lock_exists = mutex_lock_identity(lock)

    # Make sure that if any element of r is accessed, all of
    # them are executed together.
    r = nest.map_structure(tf.identity, r)

  with ops.control_dependencies([ensure_lock_exists]):
    return nest.map_structure(tf.identity, r)

While fn is running in the critical section, no other functions which wish to use this critical section may run.

Often the use case is that two executions of the same graph, in parallel, wish to run fn; and we wish to ensure that only one of them executes at a time. This is especially important if fn modifies one or more variables at a time.

It is also useful if two separate functions must share a resource, but we wish to ensure the usage is exclusive.

mutex A Tensor of type resource. The mutex resource to lock.
name A name for the operation (optional).

A Tensor of type variant.