[Support] Add file lock/unlock functions

New functions `lockFile`, `tryLockFile` and `unlockFile` implement
simple file locking. They lock or unlock entire file. This must be
enough to support simulataneous writes to log files in parallel builds.

Differential Revision: https://reviews.llvm.org/D78896

1 files changed, 45 insertions, 0 deletions

diff --git a/llvm/unittests/Support/Path.cpp b/llvm/unittests/Support/Path.cpp
index 8e842a9..92b3917 100644
--- a/llvm/unittests/Support/Path.cpp
+++ b/llvm/unittests/Support/Path.cpp
@@ -39,6 +39,8 @@
 #include <sys/stat.h>
 #endif
 
+#include <future>
+
 using namespace llvm;
 using namespace llvm::sys;
 
@@ -2038,4 +2040,47 @@ TEST_F(FileSystemTest, widenPath) {
 }
 #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));
+}
+
+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));
+
+  ASSERT_NO_ERROR(fs::tryLockFile(FD1));
+  ASSERT_ERROR(fs::tryLockFile(FD2));
+  std::future<std::error_code> Future = std::async(std::launch::async, [&] {
+    return fs::tryLockFile(FD2, std::chrono::seconds(5));
+  });
+  ASSERT_NO_ERROR(fs::unlockFile(FD1));
+  ASSERT_NO_ERROR(Future.get());
+  fs::unlockFile(FD2);
+
+  ASSERT_NO_ERROR(fs::tryLockFile(FD1));
+  ASSERT_ERROR(fs::tryLockFile(FD2));
+  Future = std::async(std::launch::async, [&] { return fs::lockFile(FD2); });
+  ASSERT_NO_ERROR(fs::unlockFile(FD1));
+  ASSERT_NO_ERROR(Future.get());
+  fs::unlockFile(FD2);
+#endif
+}
+
 } // anonymous namespace