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local-binary-cache-store: Add retry loop to upsertFile

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Handle race conditions in binary cache file creation by retrying
with a new temporary name on EEXIST errors. Uses existing
makeTempPath which already has an atomic counter.
This commit is contained in:
Jörg Thalheim 2025-06-12 17:41:13 +02:00
parent bc73faf88f
commit f124293024
1 changed files with 26 additions and 7 deletions
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33
src/libstore/local-binary-cache-store.cc
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@ -58,13 +58,32 @@ protected:
const std::string & mimeType) override
{
auto path2 = config->binaryCacheDir + "/" + path;
static std::atomic<int> counter{0};
Path tmp = fmt("%s.tmp.%d.%d", path2, getpid(), ++counter);
AutoDelete del(tmp, false);
StreamToSourceAdapter source(istream);
writeFile(tmp, source);
std::filesystem::rename(tmp, path2);
del.cancel();
/* Retry loop for handling race conditions */
while (true) {
Path tmp = makeTempPath(dirOf(path2), baseNameOf(path2) + ".tmp");
AutoDelete del(tmp, false);
StreamToSourceAdapter source(istream);
try {
writeFile(tmp, source);
} catch (Error & e) {
e.addTrace({}, "while writing to temporary file '%s' for '%s'", tmp, path2);
}
try {
std::filesystem::rename(tmp, path2);
del.cancel();
break; /* Success! */
} catch (std::filesystem::filesystem_error & e) {
if (e.code() == std::errc::file_exists) {
/* Race condition: another process created the same file.
Try again with a different name. */
continue;
}
throw SysError("renaming '%s' to '%s'", tmp, path2);
}
}
}
void getFile(const std::string & path, Sink & sink) override