use lock_gaurd to protect the access to m_exec_map in cpu_backend

src/ngraph/runtime/cpu/cpu_backend.cpp

@@ -14,6 +14,7 @@
 // limitations under the License.
 //*****************************************************************************
 
+#include <mutex>
 #include <tbb/tbb_stddef.h>
 
 #include "cpu_backend_visibility.h"
@@ -28,6 +29,10 @@
 using namespace ngraph;
 using namespace std;
 
+// this mutex will be used to protect the addition and deletion
+// of function to m_exec_map across multiple threads
+std::mutex exec_map_mutex;
+
 extern "C" runtime::BackendConstructor* get_backend_constructor_pointer()
 {
     class CPU_BackendConstructor : public runtime::BackendConstructor
@@ -90,6 +95,7 @@ shared_ptr<runtime::Executable>
                                        ngraph::pass::PassConfig& pass_config,
                                        bool performance_counters_enabled)
 {
+    std::lock_guard<std::mutex> guard(exec_map_mutex);
     shared_ptr<runtime::Executable> rc;
     auto it = m_exec_map.find(func);
     if (it != m_exec_map.end())
@@ -144,6 +150,7 @@ bool runtime::cpu::CPU_Executable::call(const vector<shared_ptr<runtime::Tensor>
 
 void runtime::cpu::CPU_Backend::remove_compiled_function(shared_ptr<Executable> exec)
 {
+    std::lock_guard<std::mutex> guard(exec_map_mutex);
     for (auto it = m_exec_map.begin(); it != m_exec_map.end(); ++it)
     {
         if (it->second == exec)