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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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38
src/libstore/download.cc
View file

@ -47,8 +47,9 @@ struct CurlDownloader : public Downloader
CurlDownloader & downloader;
DownloadRequest request;
DownloadResult result;
bool done = false; // whether the promise has been set
std::promise<DownloadResult> promise;
bool done = false; // whether either the success or failure function has been called
std::function<void(const DownloadResult &)> success;
std::function<void(std::exception_ptr exc)> failure;
CURL * req = 0;
bool active = false; // whether the handle has been added to the multi object
std::string status;
@ -86,7 +87,7 @@ struct CurlDownloader : public Downloader
if (requestHeaders) curl_slist_free_all(requestHeaders);
try {
if (!done)
fail(DownloadError(Transient, format("download of ‘%s’ was interrupted") % request.uri));
fail(DownloadError(Interrupted, format("download of ‘%s’ was interrupted") % request.uri));
} catch (...) {
ignoreException();
}
@ -95,8 +96,9 @@ struct CurlDownloader : public Downloader
template<class T>
void fail(const T & e)
{
promise.set_exception(std::make_exception_ptr(e));
assert(!done);
done = true;
failure(std::make_exception_ptr(e));
}
size_t writeCallback(void * contents, size_t size, size_t nmemb)
@ -239,7 +241,7 @@ struct CurlDownloader : public Downloader
(httpStatus == 200 || httpStatus == 304 || httpStatus == 226 /* FTP */ || httpStatus == 0 /* other protocol */))
{
result.cached = httpStatus == 304;
promise.set_value(result);
success(result);
done = true;
} else {
Error err =
@ -253,9 +255,11 @@ struct CurlDownloader : public Downloader
attempt++;
auto exc =
httpStatus != 0
? DownloadError(err, format("unable to download ‘%s’: HTTP error %d") % request.uri % httpStatus)
: DownloadError(err, format("unable to download ‘%s’: %s (%d)") % request.uri % curl_easy_strerror(code) % code);
code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
? DownloadError(Interrupted, format("download of ‘%s’ was interrupted") % request.uri)
: httpStatus != 0
? DownloadError(err, format("unable to download ‘%s’: HTTP error %d") % request.uri % httpStatus)
: DownloadError(err, format("unable to download ‘%s’: %s (%d)") % request.uri % curl_easy_strerror(code) % code);
/* If this is a transient error, then maybe retry the
download after a while. */
@ -414,7 +418,7 @@ struct CurlDownloader : public Downloader
{
try {
workerThreadMain();
} catch (Interrupted & e) {
} catch (nix::Interrupted & e) {
} catch (std::exception & e) {
printMsg(lvlError, format("unexpected error in download thread: %s") % e.what());
}
@ -437,11 +441,14 @@ struct CurlDownloader : public Downloader
writeFull(wakeupPipe.writeSide.get(), " ");
}
std::future<DownloadResult> enqueueDownload(const DownloadRequest & request) override
void enqueueDownload(const DownloadRequest & request,
std::function<void(const DownloadResult &)> success,
std::function<void(std::exception_ptr exc)> failure) override
{
auto item = std::make_shared<DownloadItem>(*this, request);
item->success = success;
item->failure = failure;
enqueueItem(item);
return item->promise.get_future();
}
};
@ -458,6 +465,15 @@ ref<Downloader> makeDownloader()
return make_ref<CurlDownloader>();
}
std::future<DownloadResult> Downloader::enqueueDownload(const DownloadRequest & request)
{
auto promise = std::make_shared<std::promise<DownloadResult>>();
enqueueDownload(request,
[promise](const DownloadResult & result) { promise->set_value(result); },
[promise](std::exception_ptr exc) { promise->set_exception(exc); });
return promise->get_future();
}
DownloadResult Downloader::download(const DownloadRequest & request)
{
return enqueueDownload(request).get();