Add folly::hardware_concurrency

Summary:
Add folly::hardware_concurrency

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum

Differential Revision: D18342219

fbshipit-source-id: 806ef7b46e52896fa289a79854e45447929ab632

folly/executors/GlobalExecutor.cpp

@@ -23,6 +23,7 @@
 #include <folly/executors/IOExecutor.h>
 #include <folly/executors/IOThreadPoolExecutor.h>
 #include <folly/executors/InlineExecutor.h>
+#include <folly/system/HardwareConcurrency.h>
 
 using namespace folly;
 
@@ -86,7 +87,7 @@ Singleton<GlobalExecutor<IOExecutor>> gGlobalIOExecutor([] {
       // Default global IO executor is an IOThreadPoolExecutor.
       [] {
         return std::make_unique<IOThreadPoolExecutor>(
-            std::thread::hardware_concurrency(),
+            folly::hardware_concurrency(),
             std::make_shared<NamedThreadFactory>("GlobalIOThreadPool"));
       });
 });

folly/system/HardwareConcurrency.cpp

+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/system/HardwareConcurrency.h>
+
+#include <thread>
+
+#include <folly/portability/Sched.h>
+
+namespace folly {
+
+unsigned int hardware_concurrency() noexcept {
+#if defined(__linux__) && !defined(__ANDROID__)
+  cpu_set_t cpuset;
+  if (!sched_getaffinity(0, sizeof(cpuset), &cpuset)) {
+    auto count = CPU_COUNT(&cpuset);
+    if (count != 0) {
+      return count;
+    }
+  }
+#endif
+
+  return std::thread::hardware_concurrency();
+}
+
+} // namespace folly

folly/system/HardwareConcurrency.h

+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+namespace folly {
+
+unsigned int hardware_concurrency() noexcept;
+
+} // namespace folly