diff --git a/llvm/include/llvm/Support/FileSystem.h b/llvm/include/llvm/Support/FileSystem.h
--- a/llvm/include/llvm/Support/FileSystem.h
+++ b/llvm/include/llvm/Support/FileSystem.h
@@ -1131,6 +1131,39 @@
 openNativeFileForRead(const Twine &Name, OpenFlags Flags = OF_None,
                       SmallVectorImpl<char> *RealPath = nullptr);
 
+/// Try to locks the file during the specified time.
+///
+/// This function implements advisory locking on entire file. If it returns
+/// <em>errc::success</em>, the file is locked by the calling process. Until the
+/// process unlocks the file by calling \a unlockFile, all attempts to lock the
+/// same file will fail/block. The process that locked the file may assume that
+/// none of other processes read or write this file, provided that all processes
+/// lock the file prior to accessing its content.
+///
+/// @param File    The descriptor representing the file to lock.
+/// @param Timeout Time in milliseconds that the process should wait before
+///                reporting lock failure. Zero value means try to get lock only
+///                once.
+/// @returns errc::success if lock is successfully obtained,
+/// errc::no_lock_available if the file cannot be locked, or platform-specific
+/// error_code otherwise.
+std::error_code
+tryLockFile(int FD,
+            std::chrono::milliseconds Timeout = std::chrono::milliseconds(0));
+
+/// Lock the file.
+///
+/// This function acts as @ref tryLockFile(int,std::chrono::milliseconds) but it
+/// waits infinitely.
+std::error_code lockFile(int FD);
+
+/// Unlock the file.
+///
+/// @param File The descriptor representing the file to unlock.
+/// @returns errc::success if lock is successfully released or platform-specific
+/// error_code otherwise.
+std::error_code unlockFile(int FD);
+
 /// @brief Close the file object.  This should be used instead of ::close for
 /// portability. On error, the caller should assume the file is closed, as is
 /// the case for Process::SafelyCloseFileDescriptor
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -31,6 +31,7 @@
 #include <sys/mman.h>
 #endif
 
+#include <sys/file.h>
 #include <dirent.h>
 #include <pwd.h>
 
@@ -1047,6 +1048,34 @@
   return NumRead;
 }
 
+std::error_code tryLockFile(int FD, std::chrono::milliseconds Timeout) {
+  auto Start = std::chrono::steady_clock::now();
+  auto End = Start + Timeout;
+  do {
+    if (::flock(FD, LOCK_EX | LOCK_NB) == 0)
+      return std::error_code();
+    int Error = errno;
+    if (Error == EWOULDBLOCK) {
+      usleep(1000);
+      continue;
+    }
+    return std::error_code(Error, std::generic_category());
+  } while (std::chrono::steady_clock::now() < End);
+  return make_error_code(errc::no_lock_available);
+}
+
+std::error_code lockFile(int FD) {
+  if (::flock(FD, LOCK_EX) == 0)
+    return std::error_code();
+  return std::error_code(errno, std::generic_category());
+}
+
+std::error_code unlockFile(int FD) {
+  if (::flock(FD, LOCK_UN) == -1)
+    return std::error_code(errno, std::generic_category());
+  return std::error_code();
+}
+
 std::error_code closeFile(file_t &F) {
   file_t TmpF = F;
   F = kInvalidFile;
diff --git a/llvm/lib/Support/Windows/Path.inc b/llvm/lib/Support/Windows/Path.inc
--- a/llvm/lib/Support/Windows/Path.inc
+++ b/llvm/lib/Support/Windows/Path.inc
@@ -1255,6 +1255,43 @@
   return readNativeFileImpl(FileHandle, Buf, &Overlapped);
 }
 
+std::error_code tryLockFile(int FD, std::chrono::milliseconds Timeout) {
+  DWORD Flags = LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY;
+  OVERLAPPED OV = {0};
+  file_t File = convertFDToNativeFile(FD);
+  auto Start = std::chrono::steady_clock::now();
+  auto End = Start + Timeout;
+  do {
+    if (::LockFileEx(File, Flags, 0, MAXDWORD, MAXDWORD, &OV))
+      return std::error_code();
+    DWORD Error = ::GetLastError();
+    if (Error == ERROR_LOCK_VIOLATION) {
+      ::Sleep(1);
+      continue;
+    }
+    return mapWindowsError(Error);
+  } while (std::chrono::steady_clock::now() < End);
+  return mapWindowsError(ERROR_LOCK_VIOLATION);
+}
+
+std::error_code lockFile(int FD) {
+  DWORD Flags = LOCKFILE_EXCLUSIVE_LOCK;
+  OVERLAPPED OV = {0};
+  file_t File = convertFDToNativeFile(FD);
+  if (::LockFileEx(File, Flags, 0, MAXDWORD, MAXDWORD, &OV))
+    return std::error_code();
+  DWORD Error = ::GetLastError();
+  return mapWindowsError(Error);
+}
+
+std::error_code unlockFile(int FD) {
+  OVERLAPPED OV = { 0 };
+  file_t File = convertFDToNativeFile(FD);
+  if (::UnlockFileEx(File, 0, MAXDWORD, MAXDWORD, &OV))
+    return std::error_code();
+  return mapWindowsError(::GetLastError());
+}
+
 std::error_code closeFile(file_t &F) {
   file_t TmpF = F;
   F = kInvalidFile;
diff --git a/llvm/unittests/Support/Path.cpp b/llvm/unittests/Support/Path.cpp
--- a/llvm/unittests/Support/Path.cpp
+++ b/llvm/unittests/Support/Path.cpp
@@ -39,6 +39,10 @@
 #include <sys/stat.h>
 #endif
 
+#include <condition_variable>
+#include <mutex>
+#include <thread>
+
 using namespace llvm;
 using namespace llvm::sys;
 
@@ -2038,4 +2042,108 @@
 }
 #endif
 
+TEST_F(FileSystemTest, lockFile) {
+  int FD1, FD2;
+  SmallString<64> TempPath;
+  ASSERT_NO_ERROR(fs::createTemporaryFile("test", "temp", FD1, TempPath));
+  FileRemover Cleanup(TempPath);
+  ASSERT_NO_ERROR(fs::openFileForReadWrite(TempPath, FD2, fs::CD_OpenExisting,
+                                           fs::OF_Append));
+  ASSERT_NO_ERROR(fs::tryLockFile(FD1));
+
+  ASSERT_EQ(errc::no_lock_available,
+            fs::tryLockFile(FD2, std::chrono::milliseconds(5)));
+  ASSERT_NO_ERROR(fs::unlockFile(FD1));
+  ASSERT_NO_ERROR(fs::tryLockFile(FD2));
+  ASSERT_NO_ERROR(fs::unlockFile(FD2));
+}
+
+namespace {
+class Event {
+  std::mutex M;
+  std::condition_variable CV;
+  bool Signaling = false;
+public:
+  void reset() { Signaling = false; }
+  void wait() {
+    std::unique_lock<std::mutex> Lock(M);
+    if (!Signaling)
+      CV.wait_for(Lock, std::chrono::seconds(1), [&] { return Signaling; });
+  }
+  void signal() {
+    std::unique_lock<std::mutex> Lock(M);
+    Signaling = true;
+    CV.notify_all();
+  }
+};
+}
+
+TEST_F(FileSystemTest, lockFileThread) {
+#if LLVM_ENABLE_THREADS
+  int FD1, FD2;
+  SmallString<64> TempPath;
+  ASSERT_NO_ERROR(fs::createTemporaryFile("test", "temp", FD1, TempPath));
+  FileRemover Cleanup(TempPath);
+  ASSERT_NO_ERROR(fs::openFileForReadWrite(TempPath, FD2, fs::CD_OpenExisting,
+                                           fs::OF_Append));
+
+  // Threads execute the following sequence:
+  //
+  //    T1 started
+  //    lock file
+  //    start T2
+  //    wait            T2 started
+  //    |               try locking file (failure)
+  //    |            /  unblock T1
+  //    unlock file     lock file
+  //                    unlock file
+
+  Event DoUnlockEvent;
+
+  std::error_code ECT2a, ECT2b;
+  bool UseBlockingCall = false;
+  const auto Thread2Body = [&]() {
+    ECT2a = fs::tryLockFile(FD2);
+    if (!ECT2a)
+      return;
+    DoUnlockEvent.signal();
+    if (UseBlockingCall)
+      ECT2b = fs::lockFile(FD2);
+    else
+      ECT2b = fs::tryLockFile(FD2, std::chrono::seconds(5));
+    if (ECT2b)
+      return;
+    fs::unlockFile(FD2);
+  };
+
+  std::error_code ECT1a, ECT1b;
+  const auto Thread1Body = [&]() {
+    ECT1a = fs::tryLockFile(FD1);
+    if (ECT1a)
+      return;
+    auto Thread2 = std::thread(Thread2Body);
+    DoUnlockEvent.wait();
+    ECT1b = fs::unlockFile(FD1);
+    Thread2.join();
+  };
+
+  auto Thread1 = std::thread(Thread1Body);
+  Thread1.join();
+  ASSERT_NO_ERROR(ECT1a);
+  ASSERT_NO_ERROR(ECT1b);
+  ASSERT_ERROR(ECT2a);
+  ASSERT_NO_ERROR(ECT2b);
+
+  UseBlockingCall = true;
+  DoUnlockEvent.reset();
+  auto Thread1a = std::thread(Thread1Body);
+  Thread1a.join();
+  ASSERT_NO_ERROR(ECT1a);
+  ASSERT_NO_ERROR(ECT1b);
+  ASSERT_ERROR(ECT2a);
+  ASSERT_NO_ERROR(ECT2b);
+
+#endif
+}
+
 } // anonymous namespace