* Redesign channel implementation for Select Op

* Remove unecessary header

* Remove unnecessary comments

* Fixing unbufered test to a generic test

* Update channel_test.cc

* splitting over functions

* add type

* fix *

* Adding more details to cluster_train

* Update copyright for notest_dist_image_classification

* Fixed copyright

* Updating the copyright year and content

Fix for program crash when destructor is called before channel close with blocked readers/writers (#8197)

* Fix destructor crash and add unit tests

* Fix typo in unit test

* Reword comments

* Make close channel a generic test

* Refactoring unit tests

* Fix method name

* Adding panic logic and test case

* Change panic behavior to boolean instead of exception

* Adding atomic

* Switch to boolean

* Fix spacing

* Add to close method

* Add test case to return zero on a closed channel

* Rename method

* Fix test

* ReceiveFromBufferedChannelReturnResidualValuesTest

* Adding the variable and case for unbuffered channel

* Fix review comments

* Fix format

* Remove a zero-value comparison

* Adding more receivers less senders

* Added more receivers less senders

* Added more send

* Updated comment

* Fixed code style

* Fixing review comments

Adding unit tests for checking that closing unbuffered channel closes all blocked senders and receivers (#8067)

* Adding unit tests for checking that closing unbuffered channel closes all blocked senders and receivers

* Fixing sleep time

* Add unite test with less receivers, more senders

* Fixed the check

* Adding an initial implementation for the unbuffered channel

* Including atomic header

* update comment

* Adding the closed attribute

* Add comments

* Updated locking mechanism

* Add simple unbuffered test

* Enhance unit test and fix bug

* Add details

* refine channel test

* follow comments

* Add dependency enforce to threadpool

* Revert changes to channel_test.cc

* Revert changes to channel_test.cc

* Add #include "paddle/framework/macros.h"

* Add unit tests

* fix code format

* refine close channel

* follow comments

* use delete to destroy channel

* Remove IsBounded as buffered channels have to be bounded

* Add derived classes Buffered and UnBuffered"

* Implement buffered and unbuffered channels

* Correct the syntax of Channel::Receive

* clang-format

* clang-format 3.8

* clang 3.8

ISSUE=4586495

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1408 1ad973e4-5ce8-4261-8a94-b56d1f490c56