file: Add LOCK subcommand to do file and directory locking

Provide options to fail without blocking or to block up to a timeout.
Provide options to specify the scope containing the lock so it can be
released automatically at the end of a function, file, or process.

Extend the RunCMake.file test with cases covering the file(LOCK) command
usage and error cases.

Source/cmFileLockUnix.cxx

@@ -0,0 +1,102 @@
+/*============================================================================
+  CMake - Cross Platform Makefile Generator
+  Copyright 2014 Ruslan Baratov
+
+  Distributed under the OSI-approved BSD License (the "License");
+  see accompanying file Copyright.txt for details.
+
+  This software is distributed WITHOUT ANY WARRANTY; without even the
+  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the License for more information.
+============================================================================*/
+
+#include "cmFileLock.h"
+
+#include <errno.h> // errno
+#include <stdio.h> // SEEK_SET
+#include <fcntl.h>
+#include "cmSystemTools.h"
+
+cmFileLock::cmFileLock(): File(-1)
+{
+}
+
+cmFileLockResult cmFileLock::Release()
+{
+  if (this->Filename.empty())
+    {
+    return cmFileLockResult::MakeOk();
+    }
+  const int lockResult = this->LockFile(F_SETLK, F_UNLCK);
+
+  this->Filename = "";
+
+  if (lockResult == 0)
+    {
+    return cmFileLockResult::MakeOk();
+    }
+  else
+    {
+    return cmFileLockResult::MakeSystem();
+    }
+}
+
+cmFileLockResult cmFileLock::OpenFile()
+{
+  this->File = ::open(this->Filename.c_str(), O_RDWR);
+  if (this->File == -1)
+    {
+    return cmFileLockResult::MakeSystem();
+    }
+  else
+    {
+    return cmFileLockResult::MakeOk();
+    }
+}
+
+cmFileLockResult cmFileLock::LockWithoutTimeout()
+{
+  if (this->LockFile(F_SETLKW, F_WRLCK) == -1)
+    {
+    return cmFileLockResult::MakeSystem();
+    }
+  else
+    {
+    return cmFileLockResult::MakeOk();
+    }
+}
+
+cmFileLockResult cmFileLock::LockWithTimeout(unsigned seconds)
+{
+  while (true)
+    {
+    if (this->LockFile(F_SETLK, F_WRLCK) == -1)
+      {
+      if (errno != EACCES && errno != EAGAIN)
+        {
+        return cmFileLockResult::MakeSystem();
+        }
+      }
+    else
+      {
+      return cmFileLockResult::MakeOk();
+      }
+    if (seconds == 0)
+      {
+      return cmFileLockResult::MakeTimeout();
+      }
+    --seconds;
+    cmSystemTools::Delay(1000);
+    }
+}
+
+int cmFileLock::LockFile(int cmd, int type)
+{
+  struct ::flock lock;
+  lock.l_start = 0;
+  lock.l_len = 0; // lock all bytes
+  lock.l_pid = 0; // unused (for F_GETLK only)
+  lock.l_type = static_cast<short>(type); // exclusive lock
+  lock.l_whence = SEEK_SET;
+  return ::fcntl(this->File, cmd, &lock);
+}