proposed improvement to temp file names used by scons cache

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Hi there,

We have a CI build framework configured such that many machines are
concurrently building and sharing a scons cache.  This cache lives on an
Amazon EFS filesystem, mounted as NFS.

In general this has been spectacularly successful, but every once in a
while corrupted files start coming out of the cache.  Our theory is that
the EFS + NFS locking guarantees aren't good enough for the SCons temp name
collision detection algorithm - attached is a patch we are going to try
running with to see if it improves things.

In addition to hoping a formalized version of this will be considered for
SCons, I'm curious if anyone sees a more likely explanation for the
symptoms described above.

--- CacheDir.py 2020-08-19 12:59:25.790302000 -0700
+++ CacheDir.py.uuid 2020-08-19 14:00:29.693749695 -0700
@@ -32,6 +32,7 @@
 import os
 import stat
 import sys
+import uuid

 import SCons.Action
 import SCons.Warnings
@@ -100,7 +101,11 @@

     cd.CacheDebug('CachePush(%s):  pushing to %s\n', t, cachefile)

-    tempfile = cachefile+'.tmp'+str(os.getpid())
+    # UUID in case filesystem doesn't support file operations well enough
to deal with multiple
+    # machines sharing a cache and attempting to write the same file at
the same time (NFS mount of
+    # AWS EFS?).
+    # TODO: Long filename concern on Windows?
+    tempfile = cachefile+'.tmp'+str(os.getpid()) + '_' + str(uuid.uuid1())
     errfmt = "Unable to copy %s to cache. Cache file is %s"

     if not fs.isdir(cachedir):

Cheers,
--
*Raven Kopelman* | Team Lead, Senior Developer

Safe Software Inc.
*T* 604.501.9985 x 331 | *F* 604.501.9965
[email protected] | www.safe.com

<http://www.safe.com/emailsignature>

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<div dir=3D"ltr"><div>Hi there,</div><div><br></div><div>We have a CI build=
 framework=20
configured such that many machines are concurrently building and sharing
 a scons cache.=C2=A0 This cache lives on an Amazon EFS filesystem, mounted=
=20
as NFS.</div><div><br></div><div>In general this has been spectacularly=20
successful, but every once in a while corrupted files start coming out=20
of the cache.=C2=A0 Our theory is that the EFS + NFS locking guarantees=20
aren&#39;t good enough for the SCons temp name collision detection algorith=
m
 - attached is a patch we are going to try running with to see if it=20
improves things.</div><div><br></div><div>In addition to hoping a=20
formalized version of this will be considered for SCons, I&#39;m curious if=
=20
anyone sees a more likely explanation for the symptoms described above.</di=
v><div><br></div><div>--- CacheDir.py	2020-08-19 12:59:25.790302000 -0700<b=
r>+++ CacheDir.py.uuid	2020-08-19 14:00:29.693749695 -0700<br>@@ -32,6 +32,=
7 @@<br>=C2=A0import os<br>=C2=A0import stat<br>=C2=A0import sys<br>+import=
 uuid<br><br>=C2=A0import SCons.Action<br>=C2=A0import SCons.Warnings<br>@@=
 -100,7 +101,11 @@<br><br>=C2=A0 =C2=A0 =C2=A0cd.CacheDebug(&#39;CachePush(=
%s): =C2=A0pushing to %s\n&#39;, t, cachefile)<br><br>- =C2=A0 =C2=A0tempfi=
le =3D cachefile+&#39;.tmp&#39;+str(os.getpid())<br>+ =C2=A0 =C2=A0# UUID i=
n case filesystem doesn&#39;t support file operations well enough to deal w=
ith multiple<br>+ =C2=A0 =C2=A0# machines sharing a cache and attempting to=
 write the same file at the same time (NFS mount of<br>+ =C2=A0 =C2=A0# AWS=
 EFS?).<br>+ =C2=A0 =C2=A0# TODO: Long filename concern on Windows?<br>+ =
=C2=A0 =C2=A0tempfile =3D cachefile+&#39;.tmp&#39;+str(os.getpid()) + &#39;=
_&#39; + str(uuid.uuid1())<br>=C2=A0 =C2=A0 =C2=A0errfmt =3D &quot;Unable t=
o copy %s to cache. Cache file is %s&quot;<br><br>=C2=A0 =C2=A0 =C2=A0if no=
t fs.isdir(cachedir):</div><div><br></div><div>Cheers,</div><div><div dir=
=3D"ltr" class=3D"gmail_signature" data-smartmail=3D"gmail_signature"><div =
dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"lt=
r"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><=
div dir=3D"ltr"><div><div dir=3D"ltr">--<br><b>Raven Kopelman</b> | Team Le=
ad, Senior Developer<br><br><div dir=3D"ltr">Safe Software Inc.</div><b>T</=
b> 604.501.9985 x 331 | <b>F</b> 604.501.9965</div><div dir=3D"ltr"><a href=
=3D"mailto:[email protected]" target=3D"_blank">[email protected]=
om</a> | <a href=3D"http://www.safe.com" target=3D"_blank">www.safe.com</a>=
</div><div dir=3D"ltr"><div><br></div><div><div><a href=3D"http://www.safe.=
com/emailsignature" target=3D"_blank"><img src=3D"http://cdn.safe.com/email=
signature.jpg"></a><br></div></div></div></div></div></div></div></div></di=
v></div></div></div></div></div></div></div></div></div></div></div></div><=
/div>

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