Add Get/SetUniqueIdForProcess.

base/process/process_handle.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_PROCESS_PROCESS_HANDLE_H_
 #define BASE_PROCESS_PROCESS_HANDLE_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/files/file_path.h"
@@ skipping 16 matching lines @@
 const ProcessHandle kNullProcessHandle = NULL;
 const ProcessId kNullProcessId = 0;
 #elif defined(OS_POSIX)
 // On POSIX, our ProcessHandle will just be the PID.
 typedef pid_t ProcessHandle;
 typedef pid_t ProcessId;
 const ProcessHandle kNullProcessHandle = 0;
 const ProcessId kNullProcessId = 0;
 #endif  // defined(OS_WIN)
 
+// This is not a valid process ID on Linux, Mac, or Windows.
+const uint32 kInvalidUniqueId = 0;
+
 // Returns the id of the current process.
 BASE_EXPORT ProcessId GetCurrentProcId();
 
+// Returns a globally unique ID for the current process. This defaults to the

[mdempsky, 2015/06/15 21:53:09]

I think "globally" might be misinterpretable.  It might be better to clarify
that the ID is unique across all live processes within the chrome session.  (I
don't think we're making a stronger guarantee than that?  I.e., other chrome
sessions can in the future reuse IDs, and if a process exits its ID can be
reused.)

[rickyz (no longer on Chrome), 2015/06/15 22:09:47]

Ah, good point, changed.

+// process process ID, but may return a different value if SetUniqueIdForProcess

[mdempsky, 2015/06/15 21:53:09]

Should "process process ID" be "process's process ID"?

[rickyz (no longer on Chrome), 2015/06/15 22:09:46]

Done.

+// has been called.
+BASE_EXPORT uint32 GetUniqueIdForProcess();
+
+// Sets the unique ID for the current process. |unique_id| may not be
+// kInvalidUniqueId.
+// WARNING: To avoid inconsistent results from GetUniqueIdForProcess, this
+// should only be called very early after process startup - ideally immediately
+// after fork.
+BASE_EXPORT void SetUniqueIdForProcess(uint32 unique_id);
+
 // Returns the ProcessHandle of the current process.
 BASE_EXPORT ProcessHandle GetCurrentProcessHandle();
 
 // Returns the unique ID for the specified process. This is functionally the
 // same as Windows' GetProcessId(), but works on versions of Windows before
 // Win XP SP1 as well.
 // DEPRECATED. New code should be using Process::Pid() instead.
 BASE_EXPORT ProcessId GetProcId(ProcessHandle process);
 
 #if defined(OS_POSIX)
 // Returns the path to the executable of the given process.
 BASE_EXPORT FilePath GetProcessExecutablePath(ProcessHandle process);
 
 // Returns the ID for the parent of the given process.
 BASE_EXPORT ProcessId GetParentProcessId(ProcessHandle process);
 #endif
 
 }  // namespace base
 
 #endif  // BASE_PROCESS_PROCESS_HANDLE_H_