* rename mkldnn set/get_cur_thread_id() to set/get_cur_mkldnn_session_id()

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* update session id definition and adjust logic for default behavior

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* reset logic in mkldnn reuse as most of cases work in default.

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* remove nccl dep when the number of GPU is 1
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* remove attribute in Allocator::Allocate, test=develop

* fix travis ci error, test=develop

* fix cuda/cudnn version detection error, test=develop

* fix again, test=develop

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* Support Sync Batch Norm.
* Note, do not enable it in one device.

Usage:

build_strategy = fluid.BuildStrategy()
build_strategy.sync_batch_norm = True
binary = fluid.compiler.CompiledProgram(tp).with_data_parallel(
        loss_name=loss_mean.name,
        build_strategy=build_strategy)

reason: dereferencing smart pointer is the same as the underlying pointer
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This reverts commit 064512aa.

* remove workspace_handle in conv2d_cudnn
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* remove workspace_handle
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* fix bug
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* make test_conv2d_op SERIAL
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* save memory in conv_cudnn
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* enhance thread safety
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* enhance temporary allocator
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* Add excess fraction
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* follow comments
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* fix bug and code refine
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* fix memory size check
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* rename reuse_tmp_allocation_excess_fraction
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* refine tensor
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* refine tensor
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* fix device_context log
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* Add Temporal Allocator

* add Temporay Allocator to DeviceContext
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* code refine
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* fix mean_iou
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* Add DeviceTemporaryAllocator
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* fix conv_op bug
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* small fix
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* code refine
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* log refine
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* fix unit test
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* move double check

* refine concat_and_split
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* add limit_of_temporary_allocation
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* fix name
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* exhaustive search for cuDNN conv.
* Refine code and add unit testing.
* Fix model load in fluid/inference and unit testing in conv2d
* Follow comments.
* Fix compiling test=develop

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This reverts commit ce7d9b07.

* exhaustive search for cuDNN conv.
* Refine code and add unit testing.
* Clean code
* Fix model load in fluid/inference and unit testing in conv2d
* Follow comments.

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Warning only at first when CUDA CC not matched.

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* feat(platform): lazy initialization of devicecontext in pool

Use std::async(deferer, []{...}) to lazy initialize DeviceContext in Pool

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* Add future includes

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