Add support for file locking

runtime/bin/file_win.cc

Index: runtime/bin/file_win.cc
diff --git a/runtime/bin/file_win.cc b/runtime/bin/file_win.cc
index 7a4b0f033f1975cb2afe798e16f222a6da249f5d..c1ead3bde145b2896bbc961f130ec192d3e6b0d5 100644
--- a/runtime/bin/file_win.cc
+++ b/runtime/bin/file_win.cc
@@ -17,6 +17,7 @@
 #include "bin/builtin.h"
 #include "bin/log.h"
 #include "bin/utils.h"
+#include "platform/utils.h"
 
 
 namespace dart {
@@ -105,6 +106,43 @@ bool File::Flush() {
 }
 
 
+bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
+  ASSERT(handle_->fd() >= 0);
+  HANDLE handle = reinterpret_cast<HANDLE>(_get_osfhandle(handle_->fd()));
+  OVERLAPPED overlapped;
+  ZeroMemory(&overlapped, sizeof(OVERLAPPED));
+
+  overlapped.Offset = Utils::Low32Bits(start);
+  overlapped.OffsetHigh = Utils::High32Bits(start);
+
+  int64_t length = end == -1 ? 0 : end - start;
+  if (length == 0) length = kMaxInt64;
+  int32_t length_low = Utils::Low32Bits(length);
+  int32_t length_high = Utils::High32Bits(length);
+
+
+  BOOL rc;
+  switch (lock) {
+    case File::kLockUnlock:
+      rc = UnlockFileEx(handle, 0, length_low, length_high, &overlapped);
+      break;
+    case File::kLockShared:
+      rc = LockFileEx(handle,
+                      LOCKFILE_FAIL_IMMEDIATELY,
+                      0, length_low, length_high, &overlapped);
+      break;
+    case File::kLockExclusive:
+      rc = LockFileEx(handle,
+                      LOCKFILE_FAIL_IMMEDIATELY | LOCKFILE_EXCLUSIVE_LOCK,
+                      0, length_low, length_high, &overlapped);
+      break;
+    default:

[Lasse Reichstein Nielsen, 2015/01/08 11:59:22]

Could these two cases be combined - they only differ on the value of the second
argument, maybe just sett a variable with that argument.

[Søren Gjesse, 2015/01/09 13:06:20]

Done.

+      return false;

[kustermann, 2015/01/08 12:54:27]

This should be UNREACHABLE()

[Søren Gjesse, 2015/01/09 13:06:20]

Done.

+  }

[kustermann, 2015/01/08 12:54:27]

Would it make sense to use GetLastError() if rc == FALSE?

[Søren Gjesse, 2015/01/09 13:06:20]

When this results in an OS error in Dart the error code from GetLastError is
already returned.

+  return rc;
+}
+
+
 int64_t File::Length() {
   ASSERT(handle_->fd() >= 0);
   struct __stat64 st;
@@ -437,7 +475,7 @@ char* File::LinkTarget(const char* pathname) {
   // Remove "\??\" from beginning of target.
   if (target_length > 4 && wcsncmp(L"\\??\\", target, 4) == 0) {
     target += 4;
-    target_length -=4;
+    target_length -= 4;
   }
   int utf8_length = WideCharToMultiByte(CP_UTF8,
                                         0,