* remove global variable

* refine code

* test=develop,test=document_fix, remove the out args

* fleet_util move to paddle.fleet
Co-authored-by: NWuHaobo <wuhaobo1994@gmail.com>
Co-authored-by: Ntangwei12 <tangwei12@baidu.com>

* add heter ps mode

* code style
test=develop

* add with_pslib
test=develop

* unitest
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* test monitor
test=develop

* prepare trainer
test=develop

* code style
test=develop

Add dgc to fleet meta optimizer, rm dgc from optimizer all

* fix dump, fix cvm check
test=develop

* fix
test=develop

* fix
test=develop

* fix
test=develop

* split meta optimizer files
* add graph execution in execution, update two properties in DistributedStrategy, unit tests for these features

* polish framework error message part 4

* fix type error

* fix message error

* polish by review comments

* fix test_pipeline, test=develop

* refine error stack format

* polish compile traceback format

* polish detail format

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

* Integrated Trainer of Parameter Server

* refine strategy compiler and meta optimizers
make async as a_sync

* simplify buffered reader to improve DataLoader performance

* fix 22 failed unittests

* fix cuda pinned context condition

* fix test_reader_reset failed

* fix two failed unittests

* change unittest place

* polish error messaage

* polish cast op GetExpecctedKernelType

* remove debug info in unittest

* add more settings for distributed strategy
Basically, DistributedStrategy has several parts of configurations:
- BuildStrategy: the same as paddle.fluid.BuildStrategy, but the distributed arguments are moved out of BuildStrategy
- ExecutionStrategy: the same as paddle.fluid.ExecutionStrategy
- collective communication configs: nccl_comm_num, hierarchical allreduce and so on
- distributed algorithms: async_update(mainly used in PS), lars, lamb and so on

* polish framework error message part3

* polish details

* fix error message print error

* Added DNNL cache management for DyGraph

* move FLAGS_use_mkldnn to more general CMakeLists, getu use of the flag in ClearGradients

* missing file

* Fixes after review

* Bringing back original idea of place for 'use_mkldnn' flag to be accessible from platform nad imperative.

* Removed duplicate and added docs

* Fixes for CI

* polish framework error meg part2

* polish details

* fix error msg report in ir/, about 19 files, test=develop

* modified some unclear descriptions, test=develop

* modified some unclear descriptions, test=develop

* modify unit test pass_test.cc, because the error report in pass.cc is used by pass_test.cc, test=develop

test=develop

* update ResetHolder, test=develop

* add TensorShare for lite engine, test=develop

* tensor data changed from copying to sharing, test=develop

* supports xpu runtime, test=develop

* fix code styles, test=develop

* polish some error message in framework, test=develop

* fix unittest error, test=develop

* replace PADDLE_ENFORCE, test=develop

* polish details based review comment, test=develop

* fix error msg report in ir/, about 5 files, test=develop

* fix error msg report in ir/, about 5 files, test=develop

* fix error msg report in ir/, about 5 files, test=develop

refactor fleet api under paddle.fleet
update DistributedStrategy

* fix paddle/fluid/framework/ir/ error msg reoprt, test=develop

* modify error msg reoprt in ir/, about errortype, grammar, supplementary infor, test=develop

* modified some unclear descriptions, test=develop

* Modify the problem that report msg is less than 20 characters, test=develop

* fix paddle/fluid/framework/ir/mkldnn/ error msg reoprt, test=develop

* modify error msg reoprt, about errortype, grammar, supplementary infor, test=develop

* modified some error descriptions, test=develop

* fix paddle/fluid/framework/ir/multi_devices_graph_pass/ error msg reoprt, test=develop

* fix paddle/fluid/framework/ir/memory_optimize_pass/ error msg reoprt, test=develop

* fix paddle/fluid/framework/ir/fuse_optimizer_ops_pass/ error msg reoprt, test=develop

* fix paddle/fluid/framework/ir/memory_optimize_pass/ error msg reoprt about PADDLE_ENFORCE, test=develop

* modify error msg reoprt,about errortype，grammar. test=develop

* modify error msg reoprt,about PADDLE_ENFORCE to PADDLE_ENFORCE_XXX, test=develop

* modify error msg reoprt,about PADDLE_ENFORCE to PADDLE_ENFORCE_XXX, and %s to %d, test=develop

* modified some error descriptions, test=develop

* fix softmax_with_cross_entropy cuda kernel overflow bug, test=develop

* replace old macro & for condition, test=develop

* polish details, test=develop

* polish pe exception process logic, test=develop

* fix unittest, test=develop

* add unittests, test=develop

* add device_worker for pipeline, test=develop

* cat bad alloc exception; test=develop

* add unitest; test=develop

* move bad alloc catch to the first place; test=develop

* polish error message; test=develop

* polish error message; test=develop

* add mutex header; test=develop

* fix multhead matmul's instable
test=develop

* fix multihead matmul bug
test=develop

* fix converage problem
test=develop

* add paddle.fleet.DistributedStrategy for 2.0

* add encrypt api for inference lib