diff --git a/absl/base/internal/sysinfo.h b/absl/base/internal/sysinfo.h
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+++ b/absl/base/internal/sysinfo.h
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+// Copyright 2017 The Abseil Authors.
+//
+// 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
+//
+//      https://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.
+//
+// This file includes routines to find out characteristics
+// of the machine a program is running on.  It is undoubtedly
+// system-dependent.
+
+// Functions listed here that accept a pid_t as an argument act on the
+// current process if the pid_t argument is 0
+// All functions here are thread-hostile due to file caching unless
+// commented otherwise.
+
+#ifndef ABSL_BASE_INTERNAL_SYSINFO_H_
+#define ABSL_BASE_INTERNAL_SYSINFO_H_
+
+#ifndef _WIN32
+#include <sys/types.h>
+#else
+#include <intsafe.h>
+#endif
+
+#include "absl/base/port.h"
+
+namespace absl {
+namespace base_internal {
+
+// Nominal core processor cycles per second of each processor.   This is _not_
+// necessarily the frequency of the CycleClock counter (see cycleclock.h)
+// Thread-safe.
+double NominalCPUFrequency();
+
+// Number of logical processors (hyperthreads) in system. Thread-safe.
+int NumCPUs();
+
+// Return the thread id of the current thread, as told by the system.
+// No two currently-live threads implemented by the OS shall have the same ID.
+// Thread ids of exited threads may be reused.   Multiple user-level threads
+// may have the same thread ID if multiplexed on the same OS thread.
+//
+// On Linux, you may send a signal to the resulting ID with kill().  However,
+// it is recommended for portability that you use pthread_kill() instead.
+#ifdef _WIN32
+// On Windows, process id and thread id are of the same type according to
+// the return types of GetProcessId() and GetThreadId() are both DWORD.
+using pid_t = DWORD;
+#endif
+pid_t GetTID();
+
+}  // namespace base_internal
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_SYSINFO_H_