Add Get/SetUniqueIdForProcess.

base/process/process_handle.h

Index: base/process/process_handle.h
diff --git a/base/process/process_handle.h b/base/process/process_handle.h
index 77f2c585cfcc71087596855fa6f83ac643ce9a6c..6a8f8d0972ba5eecae02a9cae27dc9c8ba035734 100644
--- a/base/process/process_handle.h
+++ b/base/process/process_handle.h
@@ -5,12 +5,13 @@
 #ifndef BASE_PROCESS_PROCESS_HANDLE_H_
 #define BASE_PROCESS_PROCESS_HANDLE_H_
 
+#include <stdint.h>

[danakj, 2015/08/05 19:52:26]

You want base/basictypes.h, instead of these.

[rickyz (no longer on Chrome), 2015/08/13 23:16:55]

Is that still the case?
https://code.google.com/p/chromium/codesearch#chromium/src/base/basictypes.h&...
seems to suggest using stdint instead.

+#include <sys/types.h>
+
 #include "base/base_export.h"
-#include "base/basictypes.h"
 #include "base/files/file_path.h"
 #include "build/build_config.h"
 
-#include <sys/types.h>
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
@@ -34,16 +35,37 @@ const ProcessHandle kNullProcessHandle = 0;
 const ProcessId kNullProcessId = 0;
 #endif  // defined(OS_WIN)
 
+// This is not a valid process ID on Linux (including Android), Mac, or Windows.
+const uint32_t kInvalidUniqueId = 0;

[danakj, 2015/08/05 19:52:26]

Does this need to be in the header? Can it move to the .cc file? Does other code
need to use this?

[rickyz (no longer on Chrome), 2015/08/13 23:16:55]

Don't think so, moved it into the anon namespace in the cc instead.

+
 // Returns the id of the current process.
+// Note that on some platforms, this is not guaranteed to be unique across

[danakj, 2015/08/05 19:52:26]

Who would ever want to use this one?

[rickyz (no longer on Chrome), 2015/08/13 23:16:55]

GetCurrentProcId is still useful for APIs that need a real process ID and not a
unique identifier - for example, kill or wait*.

+// processes (use GetUniqueIdForProcess if uniqueness is required).
 BASE_EXPORT ProcessId GetCurrentProcId();
 
+// Returns a unique ID for the current process. The ID will be unique across all
+// currently running processes within the chrome session, but note that IDs of
+// terminated processes may be reused. This defaults to the process's process
+// ID, but may return a different value if SetUniqueIdForProcess has been
+// called.
+BASE_EXPORT uint32_t GetUniqueIdForProcess();
+
+// Sets the unique ID for the current process. |unique_id| may not be
+// kInvalidUniqueId. Not thread safe.
+// WARNING: To avoid inconsistent results from GetUniqueIdForProcess, this
+// should only be called very early after process startup - ideally as soon
+// after process creation as possible.
+BASE_EXPORT void SetUniqueIdForProcess(uint32_t 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.
+// Returns the process 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.
+// Note that on some platforms, this is not guaranteed to be unique across

[danakj, 2015/08/05 19:52:26]

Does this mean Process:Pid() can be non-unique (always 1) as well? Can we fix
it?

[rickyz (no longer on Chrome), 2015/08/13 23:16:55]

It does, but as mentioned above, there are situations where we want the real
PID, even if it's not unique. That's why we opted to introduce a new unique ID
instead of replacing PIDs.

[danakj, 2015/09/15 18:06:39]

i think i'm not understanding something: if you're in a sandbox and your PID is
reported as 1, does using PID 1 to the kernel actually work? like if you killed
1, it would kill yourself?

+// processes.
 BASE_EXPORT ProcessId GetProcId(ProcessHandle process);
 
 #if defined(OS_POSIX)