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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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24
src/libstore/local-binary-cache-store.cc
View file

@ -32,7 +32,19 @@ protected:
void upsertFile(const std::string & path, const std::string & data) override;
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) override
{
sync2async<std::shared_ptr<std::string>>(success, failure, [&]() {
try {
return std::make_shared<std::string>(readFile(binaryCacheDir + "/" + path));
} catch (SysError & e) {
if (e.errNo == ENOENT) return std::shared_ptr<std::string>();
throw;
}
});
}
PathSet queryAllValidPaths() override
{
@ -76,16 +88,6 @@ void LocalBinaryCacheStore::upsertFile(const std::string & path, const std::stri
atomicWrite(binaryCacheDir + "/" + path, data);
}
std::shared_ptr<std::string> LocalBinaryCacheStore::getFile(const std::string & path)
{
try {
return std::make_shared<std::string>(readFile(binaryCacheDir + "/" + path));
} catch (SysError & e) {
if (e.errNo == ENOENT) return 0;
throw;
}
}
static RegisterStoreImplementation regStore([](
const std::string & uri, const Store::Params & params)
-> std::shared_ptr<Store>