* support ps-gpu

* disable heart beat UT

Integrated Trainer of Parameter Server (API add `fluid.contrib.layers.sparse_embedding` only) (#22957)

* Integrated Trainer of Parameter Server

* add retry for prefetch

* Revert "Fix/sync barrier (#25016)"

This reverts commit be6a315f.

* reopen dist UT, test=develop

* remove fl UT, test=develop

* test=develop, fix_embedding

* test=develop

* test=develop

* fix bug

* test=develop

* test=develop

* fix sync barrier with barrier monitor, test=develop

* remove REPLACE_ENFORCE_GLOG compile option & add ci rule prohibit LOG(FATAL) using, test=develop

* remove ci test case, test=develop

* replace all LOG(FATAL) & polish message, test=develop

* fix typo, test=develop

* polish error info detail, test=develop

* add new macro BOOST_GET_SAFELY & unittests, test=develop

* add different macro type, test=develop

* fix get macro type in executor, test=develop

* four macro part change backup

* using one macro for all case, test=develop

* revert attribute change, test=develop

* change to three func to solve gcc4.8 bug, test=develop

* polish some details, test=develop

* Make optimizer consistent in dygraph and static-graph and remove some LOG-INFO

* fix communicator when breaking under PyReader mode, test=develop
* revert some vlog level to 0, test=develop

* add sync communicator and implement

Compile without nccl deps. [1/2]
Co-authored-by: N石晓伟 <39303645+Shixiaowei02@users.noreply.github.com>

* test=develop, fix geo Send & Init

* add half_async in the communicator
* fix DistributedStrategy

* test=develop, bug fix for sparse recorder

* add distributed_strategy

* test=develop, speed dense calc & communication

* add fake init for the trainer, fix large memory hold in the trainer
* do not merge recv vars from a remote endpoint, test=develop
* add recv and save op, merge slice var in one op, save memory
* remove hsigmoid with pull sparse, test=develop

test=develop

* fix -Wno-error=sign-compare warning in gcc8

test=develop

* fix warning in distributed codes

test=develop

* remove -Wno-error=sign-compare, make warning as error

test=develop test=document_fix

* fix exist compile warning

test=develop

* test=develop,fix rpc not wait in geo

* update pserver decay blocks

* update distributed notify handler

* fix PaddleCloud Role maker & add warning in distribute transpiler  & change rpc_retry_times

* test=develop, communicator_is_sgd_optimizer flags

* test=develop,Fix communicator slow bug

* test=develop, delete if() in stop_worker()

* test=develop

* fix UT, test=develop

* fix bug in fetch handler, test=develop

* fix bug in fetch handler, test=develop

* test=develop, fix fetch barrier bug

* test=develop, bug fix

* test=develop, bug fix

* test=develop, fix bug

* bug fix: invalid learning rate decay in pserver async mode

* delete debug vlog & add rpc function & fix word2vec bug & speed GEO-SGD

add executor.FetchHandler for train/infer from the dataset

Heartbeat for distributed async training.

* refector geo sgd & communicator

* add a base class for the Communicator
* add AsyncCommunicator Impl for async distributed training