说明：转载自 Android Camera，不定期添加自己的学习思考。
Request Creation and Submission
Default requests
To construct default capture requests, call ICameraDeviceSession::constructDefaultRequestSettings().
Request submission
To submit camera capture requests, call ICameraDeviceSession::processCaptureRequest().
Miscellaneous methods
Request/result message queues
Camera capture result and request IPC overhead can be further optimized with fast message queues. Call the ICameraDeviceSession::getCaptureRequestMetadataQueue() and ICameraDeviceSession::getCaptureResultMetadataQueue() methods to query the corresponding queues.
Flushing requests
To flush any pending capture requests, call ICameraDeviceSession::flush().
