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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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32
src/libstore/binary-cache-store.cc
View file

@ -12,6 +12,8 @@
#include <chrono>
#include <future>
namespace nix {
BinaryCacheStore::BinaryCacheStore(const Params & params)
@ -58,6 +60,19 @@ void BinaryCacheStore::notImpl()
throw Error("operation not implemented for binary cache stores");
}
std::shared_ptr<std::string> BinaryCacheStore::getFile(const std::string & path)
{
std::promise<std::shared_ptr<std::string>> promise;
getFile(path,
[&](std::shared_ptr<std::string> result) {
promise.set_value(result);
},
[&](std::exception_ptr exc) {
promise.set_exception(exc);
});
return promise.get_future().get();
}
Path BinaryCacheStore::narInfoFileFor(const Path & storePath)
{
assertStorePath(storePath);
@ -176,17 +191,22 @@ void BinaryCacheStore::narFromPath(const Path & storePath, Sink & sink)
sink((unsigned char *) nar->c_str(), nar->size());
}
std::shared_ptr<ValidPathInfo> BinaryCacheStore::queryPathInfoUncached(const Path & storePath)
void BinaryCacheStore::queryPathInfoUncached(const Path & storePath,
std::function<void(std::shared_ptr<ValidPathInfo>)> success,
std::function<void(std::exception_ptr exc)> failure)
{
auto narInfoFile = narInfoFileFor(storePath);
auto data = getFile(narInfoFile);
if (!data) return 0;
auto narInfo = make_ref<NarInfo>(*this, *data, narInfoFile);
getFile(narInfoFile,
[=](std::shared_ptr<std::string> data) {
if (!data) return success(0);
stats.narInfoRead++;
stats.narInfoRead++;
return std::shared_ptr<NarInfo>(narInfo);
callSuccess(success, failure, (std::shared_ptr<ValidPathInfo>)
std::make_shared<NarInfo>(*this, *data, narInfoFile));
},
failure);
}
Path BinaryCacheStore::addToStore(const string & name, const Path & srcPath,