Add Locking calls to file_io.h plus implementations and test

util/file/file_io_posix.cc

Index: util/file/file_io_posix.cc
diff --git a/util/file/file_io_posix.cc b/util/file/file_io_posix.cc
index 60bc9a8daaac1473a1f49c01f76433c77cc7b7e7..28e06a9fbe9b4572ac561ce4522c87d9aabe4129 100644
--- a/util/file/file_io_posix.cc
+++ b/util/file/file_io_posix.cc
@@ -15,6 +15,7 @@
 #include "util/file/file_io.h"
 
 #include <fcntl.h>
+#include <sys/file.h>
 #include <unistd.h>
 
 #include "base/files/file_path.h"
@@ -100,6 +101,19 @@ FileHandle LoggingOpenFileForWrite(const base::FilePath& path,
   return fd;
 }
 
+bool LoggingLockFile(FileHandle file, FileLocking locking) {
+  int operation = locking == FileLocking::kShared ? LOCK_SH : LOCK_EX;
+  int rv = HANDLE_EINTR(flock(file, operation));
+  PLOG_IF(ERROR, rv < 0) << "flock";

[Mark Mentovai, 2015/03/20 22:11:36]

You’ll get slightly better machine code if you make the conditions on this line
and the next line true inverses. The compiler won’t typically know that flock()
can only return 0 or -1. Same in the unlock case.

[scottmg, 2015/03/20 22:32:53]

Done.

+  return rv == 0;
+}
+
+bool LoggingUnlockFile(FileHandle file) {
+  int rv = flock(file, LOCK_UN);
+  PLOG_IF(ERROR, rv < 0) << "flock";
+  return rv == 0;
+}
+
 FileOffset LoggingSeekFile(FileHandle file, FileOffset offset, int whence) {
   off_t rv = lseek(file, offset, whence);
   PLOG_IF(ERROR, rv < 0) << "lseek";