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Make computeFSClosure() single-threaded again

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The fact that queryPathInfo() is synchronous meant that we needed a
thread for every concurrent binary cache lookup, even though they end
up being handled by the same download thread. Requiring hundreds of
threads is not a good idea. So now there is an asynchronous version of
queryPathInfo() that takes a callback function to process the
result. Similarly, enqueueDownload() now takes a callback rather than
returning a future.

Thus, a command like

  nix path-info --store https://cache.nixos.org/ -r /nix/store/slljrzwmpygy1daay14kjszsr9xix063-nixos-16.09beta231.dccf8c5

that returns 4941 paths now takes 1.87s using only 2 threads (the main
thread and the downloader thread). (This is with a prewarmed
CloudFront.)
This commit is contained in:
Eelco Dolstra 2016-09-16 18:54:14 +02:00
parent 054be50257
commit 75989bdca7
16 changed files with 410 additions and 227 deletions
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25
src/libstore/http-binary-cache-store.cc
View file

@ -69,18 +69,27 @@ protected:
throw UploadToHTTP("uploading to an HTTP binary cache is not supported");
}
std::shared_ptr<std::string> getFile(const std::string & path) override
void getFile(const std::string & path,
std::function<void(std::shared_ptr<std::string>)> success,
std::function<void(std::exception_ptr exc)> failure)
{
DownloadRequest request(cacheUri + "/" + path);
request.showProgress = DownloadRequest::no;
request.tries = 8;
try {
return getDownloader()->download(request).data;
} catch (DownloadError & e) {
if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
return 0;
throw;
}
getDownloader()->enqueueDownload(request,
[success](const DownloadResult & result) {
success(result.data);
},
[success, failure](std::exception_ptr exc) {
try {
std::rethrow_exception(exc);
} catch (DownloadError & e) {
if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
success(0);
failure(exc);
}
});
}
};