@Override
              public Object call() throws Exception {
                startLatch.countDown();
                channel.transferFrom(new ByteBufferChannel(buffer), 0, 10);
                return null;
              }
Queues blocking operations on the channel in separate threads using the given executor. The
given latch should have a count of BLOCKING_OP_COUNT to allow the caller wants to wait for all
threads to start executing.
jimfs/src/test/java/com/google/common/jimfs/JimfsFileChannelTest.java