lix/src/libstore/http-binary-cache-store.cc
Eelco Dolstra 75989bdca7 Make computeFSClosure() single-threaded again
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.)
2016-09-16 18:54:14 +02:00

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#include "binary-cache-store.hh"
#include "download.hh"
#include "globals.hh"
#include "nar-info-disk-cache.hh"
namespace nix {
MakeError(UploadToHTTP, Error);
class HttpBinaryCacheStore : public BinaryCacheStore
{
private:
Path cacheUri;
public:
HttpBinaryCacheStore(
const Params & params, const Path & _cacheUri)
: BinaryCacheStore(params)
, cacheUri(_cacheUri)
{
if (cacheUri.back() == '/')
cacheUri.pop_back();
diskCache = getNarInfoDiskCache();
}
std::string getUri() override
{
return cacheUri;
}
void init() override
{
// FIXME: do this lazily?
if (!diskCache->cacheExists(cacheUri, wantMassQuery_, priority)) {
try {
BinaryCacheStore::init();
} catch (UploadToHTTP &) {
throw Error(format("%s does not appear to be a binary cache") % cacheUri);
}
diskCache->createCache(cacheUri, storeDir, wantMassQuery_, priority);
}
}
protected:
bool fileExists(const std::string & path) override
{
try {
DownloadRequest request(cacheUri + "/" + path);
request.showProgress = DownloadRequest::no;
request.head = true;
request.tries = 5;
getDownloader()->download(request);
return true;
} catch (DownloadError & e) {
/* S3 buckets return 403 if a file doesn't exist and the
bucket is unlistable, so treat 403 as 404. */
if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
return false;
throw;
}
}
void upsertFile(const std::string & path, const std::string & data) override
{
throw UploadToHTTP("uploading to an HTTP binary cache is not supported");
}
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;
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);
}
});
}
};
static RegisterStoreImplementation regStore([](
const std::string & uri, const Store::Params & params)
-> std::shared_ptr<Store>
{
if (std::string(uri, 0, 7) != "http://" &&
std::string(uri, 0, 8) != "https://" &&
(getEnv("_NIX_FORCE_HTTP_BINARY_CACHE_STORE") != "1" || std::string(uri, 0, 7) != "file://")
) return 0;
auto store = std::make_shared<HttpBinaryCacheStore>(params, uri);
store->init();
return store;
});
}