Execute a temp copy of update_depot_tools.bat

update_depot_tools.bat

Index: update_depot_tools.bat
diff --git a/update_depot_tools.bat b/update_depot_tools.bat
index f880d9b895a384c616915c6d1f4ce5bc7c063319..340c0147831415df6a4f773ff9d61b845024027f 100644
--- a/update_depot_tools.bat
+++ b/update_depot_tools.bat
@@ -7,6 +7,15 @@
 
 setlocal
 
+:: Windows sometimes freaks out if a file is overwritten while it's being

[iannucci, 2013/03/20 21:06:14]

'sometimes'?

[szager1, 2013/03/20 21:19:10]

I haven't explored every nuance of this behavior (e.g., what happens with
subprocesses, or exec from bash, or ...).  But I can reproduce the bad
situation, if necessary.

[iannucci, 2013/03/20 21:33:14]

I was meaning that the 'sometimes' can just be omitted :). I believe that batch
scripts are modifiable 'live', so if svn pulls a change which moves all the
lines in the batch file, cmd.exe could end up skipping a line or executing a
line (or lines(s)) multiple times. See 'Compound Modification' in
http://en.wikipedia.org/wiki/Self-modifying_code

[M-A Ruel, 2013/03/20 21:51:22]

Exact, cmd.exe keeps a byte offset and re-reads the file on every line. No
wonder batch files are slow as molasse.

[szager1, 2013/03/20 21:53:52]

OK, I removed 'sometimes'.  Why give false hope?

+:: executed.  Copy this script off to a temporary location and reinvoke from
+:: there before running any svn or git commands.
+IF %~nx0==update_depot_tools.bat (
+  COPY /Y %~dp0update_depot_tools.bat %~dp0update_depot_tools_tmp.bat >nul

[iannucci, 2013/03/20 21:06:14]

is %~dp guaranteed to end with a r'\' ?

[M-A Ruel, 2013/03/20 21:06:37]

Please use %TEMP%\update_depot_tools_%RANDOM%.bat, so the likelihood of 2
gclient process breaking each other lowers from 100% to 1/~10000, since we can't
trust the random number generator to be efficient. You could use
%RANDOM%_%RANDOM% if you prefer but since it's a pseudo-random generator, it
won't help much.

[szager1, 2013/03/20 21:19:10]

That means that I have to fix every occurence of %~dp0 in this file.  Which I
can do, but I was hoping to leave a smaller footprint.

Do we really claim to support multiple concurrent invocations of gclient?

[M-A Ruel, 2013/03/20 21:51:22]

I don't mind about not using random but you should still put it in TEMP.

[szager1, 2013/03/20 21:53:52]

Hmmm... I've never seen it any other way.

[szager1, 2013/03/20 21:53:52]

Hmmm... I've never seen it any other way.  Theoretically, if the script was at
the top directory level, I suppose that might not be true.  But if that happens,
I'd just as soon this script died, since you're clearly in a bad state.

[szager1, 2013/03/20 22:03:44]

Done.

+  if errorlevel 1 goto :EOF
+  %~dp0update_depot_tools_tmp.bat %*

[iannucci, 2013/03/20 21:06:14]

Should we goto :EOF after this? I forget how batch subinvocations work...

[szager1, 2013/03/20 21:19:10]

Empirical evidence suggests that it's not necessary, but I'll add it anyways,
just to be safe.

[M-A Ruel, 2013/03/20 21:51:22]

No it's not necessary. As long as there is not 'call' statement, the control is
deferred to the called batch file.

+)
+
 set GIT_URL=https://chromium.googlesource.com/chromium/tools/depot_tools.git
 
 :: Will download svn and python.