Refactor LibraryInitializer so it's thread safe. Fixes random sporadi…

…cal concurrency crashes. (apache#15762)

* Refactor LibraryInitializer so it's thread safe.
Fixes apache#13438
Fixes apache#14979

* Refactor around lib loading

* Fix lint

* CR

* Add option to choose between OMP implementations

* Fix bug

* Fix from CR

CMakeLists.txt

@@ -24,6 +24,7 @@ mxnet_option(USE_OLDCMAKECUDA     "Build with old cmake cuda" OFF)
 mxnet_option(USE_NCCL             "Use NVidia NCCL with CUDA" OFF)
 mxnet_option(USE_OPENCV           "Build with OpenCV support" ON)
 mxnet_option(USE_OPENMP           "Build with Openmp support" ON)
+mxnet_option(USE_OPENMP_BUNDLED_LLVM "Build with bundled llvm openmp from 3rdparty" OFF)
 mxnet_option(USE_CUDNN            "Build with cudnn support"  ON) # one could set CUDNN_ROOT for search path
 mxnet_option(USE_SSE              "Build with x86 SSE instruction support" ON IF NOT ARM)
 mxnet_option(USE_F16C             "Build with x86 F16C instruction support" ON) # autodetects support if ON
@@ -433,11 +434,11 @@ if(USE_OPENMP)
   find_package(OpenMP REQUIRED)
   # This should build on Windows, but there's some problem and I don't have a Windows box, so
   # could a Windows user please fix?
-  if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/openmp/CMakeLists.txt
-     AND SYSTEM_ARCHITECTURE STREQUAL "x86_64"
-     AND NOT MSVC
-     AND NOT CMAKE_CROSSCOMPILING)
-
+  if(USE_OPENMP_BUNDLED_LLVM AND EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/openmp/CMakeLists.txt
+      AND SYSTEM_ARCHITECTURE STREQUAL "x86_64"
+      AND NOT MSVC
+      AND NOT CMAKE_CROSSCOMPILING)
+    message("Using bundlded LLVM OpenMP")
     # Intel/llvm OpenMP: https://github.com/llvm-mirror/openmp
     set(OPENMP_STANDALONE_BUILD TRUE)
     set(LIBOMP_ENABLE_SHARED TRUE)
@@ -451,6 +452,7 @@ if(USE_OPENMP)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
     add_definitions(-DMXNET_USE_OPENMP=1)
   else()
+    message("Using platform provided OpenMP")
     if(OPENMP_FOUND)
       set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
       set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")

docs/faq/env_var.md

@@ -39,6 +39,9 @@ $env:MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
 
 ## Set the Number of Threads
 
+* MXNET_OMP_MAX_THREADS
+  - Values: Int ```(default=Number of processors / Number of processors * 2 in X86)```
+  - Maximum number of threads to use in individual operators through OpenMP. If not set, OMP_NUM_THREADS is considered after.
 * MXNET_GPU_WORKER_NTHREADS
   - Values: Int ```(default=2)```
   - The maximum number of threads to use on each GPU. This parameter is used to parallelize the computation within a single GPU card.
@@ -47,7 +50,7 @@ $env:MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
   - The maximum number of concurrent threads that do the memory copy job on each GPU.
 * MXNET_CPU_WORKER_NTHREADS
   - Values: Int ```(default=1)```
-  - The maximum number of scheduling threads on CPU. It specifies how many operators can be run in parallel. Note that most CPU operators are parallelized by OpenMP. To change the number of threads used by individual operators, please set `OMP_NUM_THREADS` instead.
+  - The maximum number of scheduling threads on CPU. It specifies how many operators can be run in parallel. Note that most CPU operators are parallelized by OpenMP. To change the number of threads used by individual operators, please set `MXNET_OMP_MAX_THREADS` instead.
 * MXNET_CPU_PRIORITY_NTHREADS
   - Values: Int ```(default=4)```
   - The number of threads given to prioritized CPU jobs.
@@ -56,10 +59,13 @@ $env:MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
   - The number of threads used for NNPACK. NNPACK package aims to provide high-performance implementations of some layers for multi-core CPUs. Checkout [NNPACK](http://mxnet.io/faq/nnpack.html) to know more about it.
 * MXNET_MP_WORKER_NTHREADS
   - Values: Int ```(default=1)```
-  - The number of scheduling threads on CPU given to multiprocess workers. Enlarge this number allows more operators to run in parallel in individual workers but please consider reducing the overall `num_workers` to avoid thread contention (not available on Windows).
+  - The number of scheduling threads on CPU given to multiprocess workers (after fork). Enlarge this number allows more operators to run in parallel in individual workers but please consider reducing the overall `num_workers` to avoid thread contention (not available on Windows).
 * MXNET_MP_OPENCV_NUM_THREADS
   - Values: Int ```(default=0)```
   - The number of OpenCV execution threads given to multiprocess workers. OpenCV multithreading is disabled if `MXNET_MP_OPENCV_NUM_THREADS` < 1 (default). Enlarge this number may boost the performance of individual workers when executing underlying OpenCV functions but please consider reducing the overall `num_workers` to avoid thread contention (not available on Windows).
+* MXNET_GPU_COPY_NTHREADS
+  - Values:: Int ```(default=2)```
+  - Number of threads for copying data from CPU to GPU.
 
 ## Memory Options
 

src/c_api/c_api.cc

@@ -46,12 +46,12 @@
 #include "mxnet/libinfo.h"
 #include "mxnet/imperative.h"
 #include "mxnet/lib_api.h"
+#include "../initialize.h"
 #include "./c_api_common.h"
 #include "../operator/custom/custom-inl.h"
 #include "../operator/tensor/matrix_op-inl.h"
 #include "../operator/tvmop/op_module.h"
 #include "../common/utils.h"
-#include "../common/library.h"
 
 using namespace mxnet;
 
@@ -95,7 +95,7 @@ inline int MXAPIGetFunctionRegInfo(const FunRegType *e,
 // Loads library and initializes it
 int MXLoadLib(const char *path) {
   API_BEGIN();
-  void *lib = load_lib(path);
+  void *lib = LibraryInitializer::Get()->lib_load(path);
   if (!lib)
     LOG(FATAL) << "Unable to load library";
 

src/common/utils.h

@@ -50,9 +50,21 @@
 #include "../operator/nn/mkldnn/mkldnn_base-inl.h"
 #endif
 
+#if defined(_WIN32) || defined(_WIN64) || defined(__WINDOWS__)
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
+
 namespace mxnet {
 namespace common {
 
+#if defined(_WIN32) || defined(_WIN64) || defined(__WINDOWS__)
+inline size_t current_process_id() { return ::GetCurrentProcessId(); }
+#else
+inline size_t current_process_id() { return getpid(); }
+#endif
 /*!
  * \brief IndPtr should be non-negative, in non-decreasing order, start with 0
  *           and end with value equal with size of indices.

src/engine/threaded_engine_perdevice.cc

@@ -28,6 +28,7 @@
 #include <dmlc/parameter.h>
 #include <dmlc/concurrency.h>
 #include <dmlc/thread_group.h>
+#include "../initialize.h"
 #include "./threaded_engine.h"
 #include "./thread_pool.h"
 #include "../common/lazy_alloc_array.h"
@@ -76,7 +77,8 @@ class ThreadedEnginePerDevice : public ThreadedEngine {
   void Start() override {
     if (is_worker_) return;
     gpu_worker_nthreads_ = common::GetNumThreadsPerGPU();
-    cpu_worker_nthreads_ = dmlc::GetEnv("MXNET_CPU_WORKER_NTHREADS", 1);
+    // MXNET_CPU_WORKER_NTHREADS
+    cpu_worker_nthreads_ = LibraryInitializer::Get()->cpu_worker_nthreads_;
     gpu_copy_nthreads_ = dmlc::GetEnv("MXNET_GPU_COPY_NTHREADS", 2);
     // create CPU task
     int cpu_priority_nthreads = dmlc::GetEnv("MXNET_CPU_PRIORITY_NTHREADS", 4);