libstore: fix queryValidPaths concurrency

The lock usage was obviously wrong so it was entirely serialized. This
has the predicted speedups, the only question is whether it is sound
because it's exposing a bunch of new code to actual concurrency.

I did audit all the stores' queryPathInfoUncached implementations and
they all look *intended* to be thread safe, but whether that is actually
sound or not: lol lmao. I am highly confident in the s3 one because it
is calling s3 sdk methods that are thread safe and has no actual state.

Others are using Pool and look to be *supposed* to be thread safe, but
unsure if they actually are.

Change-Id: I0369152a510e878b5ac56c9ac956a98d48cd5fef

meson.build

@@ -222,7 +222,8 @@ brotli = [
 
 openssl = dependency('libcrypto', 'openssl', required : true)
 
-aws_sdk = dependency('aws-cpp-sdk-core', required : false)
+# FIXME: confirm we actually support such old versions of aws-sdk-cpp
+aws_sdk = dependency('aws-cpp-sdk-core', required : false, version : '>=1.8')
 aws_sdk_transfer = dependency('aws-cpp-sdk-transfer', required : aws_sdk.found(), fallback : ['aws_sdk', 'aws_cpp_sdk_transfer_dep'])
 if aws_sdk.found()
   # The AWS pkg-config adds -std=c++11.
@@ -234,12 +235,6 @@ if aws_sdk.found()
     links : true,
     sources : true,
   )
-  s = aws_sdk.version().split('.')
-  configdata += {
-    'AWS_VERSION_MAJOR': s[0].to_int(),
-    'AWS_VERSION_MINOR': s[1].to_int(),
-    'AWS_VERSION_PATCH': s[2].to_int(),
-  }
   aws_sdk_transfer = aws_sdk_transfer.partial_dependency(
     compile_args : false,
     includes : true,

src/build-remote/build-remote.cc

@@ -60,7 +60,7 @@ static bool allSupportedLocally(Store & store, const std::set<std::string>& requ
 static int main_build_remote(int argc, char * * argv)
 {
     {
-        logger = makeJSONLogger(*logger);
+        logger.replace(makeJSONLogger(*logger));
 
         /* Ensure we don't get any SSH passphrase or host key popups. */
         unsetenv("DISPLAY");

src/libmain/loggers.cc

@@ -20,14 +20,14 @@ LogFormat parseLogFormat(const std::string & logFormatStr) {
     throw Error("option 'log-format' has an invalid value '%s'", logFormatStr);
 }
 
-Logger * makeDefaultLogger() {
+std::shared_ptr<Logger> makeDefaultLogger() {
     switch (defaultLogFormat) {
     case LogFormat::raw:
         return makeSimpleLogger(false);
     case LogFormat::rawWithLogs:
         return makeSimpleLogger(true);
     case LogFormat::internalJSON:
-        return makeJSONLogger(*makeSimpleLogger(true));
+        return makeJSONLogger(makeSimpleLogger(true));
     case LogFormat::bar:
         return makeProgressBar();
     case LogFormat::barWithLogs: {
@@ -50,7 +50,7 @@ void setLogFormat(const LogFormat & logFormat) {
 }
 
 void createDefaultLogger() {
-    logger = makeDefaultLogger();
+    logger.replace(makeDefaultLogger());
 }
 
 }

src/libmain/progress-bar.cc

@@ -1,10 +1,10 @@
 #include "progress-bar.hh"
+#include "file-system.hh"
+#include "strings.hh"
 #include "sync.hh"
-#include "store-api.hh"
 #include "names.hh"
 #include "terminal.hh"
 
-#include <atomic>
 #include <map>
 #include <thread>
 #include <sstream>
@@ -119,7 +119,18 @@ public:
     {
         {
             auto state(state_.lock());
-            if (!state->active) return;
+            if (!state->active) {
+                // Unlock immediately so we don't deadlock.
+                {
+                    auto _ = std::move(state);
+                }
+                // Even if the thread is inactive, the handle needs to be
+                // explicitly joined to not call terminate if it is destructed.
+                if (updateThread.joinable()) {
+                    updateThread.join();
+                }
+                return;
+            }
             state->active = false;
             writeToStderr("\r\e[K");
             updateCV.notify_one();
@@ -531,19 +542,19 @@ public:
     }
 };
 
-Logger * makeProgressBar()
+std::shared_ptr<Logger> makeProgressBar()
 {
-    return new ProgressBar(shouldANSI());
+    return std::make_shared<ProgressBar>(shouldANSI());
 }
 
 void startProgressBar()
 {
-    logger = makeProgressBar();
+    logger.replace(makeProgressBar());
 }
 
 void stopProgressBar()
 {
-    auto progressBar = dynamic_cast<ProgressBar *>(logger);
+    auto progressBar = dynamic_cast<ProgressBar *>(&**logger);
     if (progressBar) progressBar->stop();
 
 }

src/libmain/progress-bar.hh

@@ -5,7 +5,7 @@
 
 namespace nix {
 
-Logger * makeProgressBar();
+std::shared_ptr<Logger> makeProgressBar();
 
 void startProgressBar();
 

src/libstore/build/child.cc

@@ -5,7 +5,7 @@ namespace nix {
 
 void commonChildInit()
 {
-    logger = makeSimpleLogger();
+    logger.replace(makeSimpleLogger());
 
     const static std::string pathNullDevice = "/dev/null";
     restoreProcessContext(false);

src/libstore/build/derivation-goal.cc

@@ -873,9 +873,9 @@ void DerivationGoal::cleanupPostOutputsRegisteredModeNonCheck()
 {
 }
 
-void runPostBuildHook(
+static void runPostBuildHook(
     Store & store,
-    Logger & logger,
+    std::shared_ptr<Logger> logger,
     const StorePath & drvPath,
     const StorePathSet & outputPaths)
 {

src/libstore/build/local-derivation-goal.cc

@@ -2156,7 +2156,7 @@ void LocalDerivationGoal::runChild()
         /* Execute the program.  This should not return. */
         if (drv->isBuiltin()) {
             try {
-                logger = makeJSONLogger(*logger);
+                logger.replace(makeJSONLogger(*logger));
 
                 BasicDerivation & drv2(*drv);
                 for (auto & e : drv2.env)

src/libstore/daemon.cc

@@ -263,7 +263,7 @@ struct ClientSettings
     }
 };
 
-static void performOp(TunnelLogger * logger, ref<Store> store,
+static void performOp(std::shared_ptr<TunnelLogger> logger, ref<Store> store,
     TrustedFlag trusted, RecursiveFlag recursive, WorkerProto::Version clientVersion,
     Source & from, BufferedSink & to, WorkerProto::Op op)
 {
@@ -1014,11 +1014,11 @@ void processConnection(
     if (clientVersion < 0x10a)
         throw Error("the Nix client version is too old");
 
-    auto tunnelLogger = new TunnelLogger(to, clientVersion);
-    auto prevLogger = nix::logger;
+    auto tunnelLogger = std::make_shared<TunnelLogger>(to, clientVersion);
+    auto prevLogger = *nix::logger;
     // FIXME
     if (!recursive)
-        logger = tunnelLogger;
+        prevLogger = nix::logger.replace(tunnelLogger);
 
     unsigned int opCount = 0;
 

src/libstore/s3-binary-cache-store.cc

@@ -55,12 +55,14 @@ class AwsLogger : public Aws::Utils::Logging::FormattedLogSystem
 
     void ProcessFormattedStatement(Aws::String && statement) override
     {
+        // FIXME: workaround for truly excessive log spam in debug level: https://github.com/aws/aws-sdk-cpp/pull/3003
+        if ((statement.find("(SSLDataIn)") != std::string::npos || statement.find("(SSLDataOut)") != std::string::npos) && verbosity <= lvlDebug) {
+            return;
+        }
         debug("AWS: %s", chomp(statement));
     }
 
-#if !(AWS_VERSION_MAJOR <= 1 && AWS_VERSION_MINOR <= 7 && AWS_VERSION_PATCH <= 115)
     void Flush() override {}
-#endif
 };
 
 static void initAWS()
@@ -100,12 +102,7 @@ S3Helper::S3Helper(
             : std::dynamic_pointer_cast<Aws::Auth::AWSCredentialsProvider>(
                 std::make_shared<Aws::Auth::ProfileConfigFileAWSCredentialsProvider>(profile.c_str())),
             *config,
-            // FIXME: https://github.com/aws/aws-sdk-cpp/issues/759
-#if AWS_VERSION_MAJOR == 1 && AWS_VERSION_MINOR < 3
-            false,
-#else
             Aws::Client::AWSAuthV4Signer::PayloadSigningPolicy::Never,
-#endif
             endpoint.empty()))
 {
 }

src/libstore/store-api.cc

@@ -792,17 +792,31 @@ StorePathSet Store::queryValidPaths(const StorePathSet & paths, SubstituteFlag m
 
     auto doQuery = [&](const StorePath & path) {
         checkInterrupt();
-        auto state(state_.lock());
+
+        bool exists = false;
+        std::optional<std::exception_ptr> newExc;
+
         try {
-            auto info = queryPathInfo(path);
-            state->valid.insert(path);
+            queryPathInfo(path);
+            exists = true;
         } catch (InvalidPath &) {
         } catch (...) {
-            state->exc = std::current_exception();
+            newExc = std::current_exception();
+        }
+
+        {
+            auto state(state_.lock());
+
+            if (exists) {
+                state->valid.insert(path);
+            }
+            if (newExc.has_value()) {
+                state->exc = *newExc;
             }
             assert(state->left);
             if (!--state->left)
                 wakeup.notify_one();
+        }
     };
 
     for (auto & path : paths)
@@ -1163,22 +1177,27 @@ std::map<StorePath, StorePath> copyPaths(
         ValidPathInfo infoForDst = *info;
         infoForDst.path = storePathForDst;
 
-        auto source = sinkToSource([&](Sink & sink) {
+        auto source =
+            sinkToSource([&srcStore, &dstStore, missingPath = missingPath, info = std::move(info)](Sink & sink) {
                 // We can reasonably assume that the copy will happen whenever we
                 // read the path, so log something about that at that point
                 auto srcUri = srcStore.getUri();
                 auto dstUri = dstStore.getUri();
                 auto storePathS = srcStore.printStorePath(missingPath);
-            Activity act(*logger, lvlInfo, actCopyPath,
+                Activity act(
+                    *logger,
+                    lvlInfo,
+                    actCopyPath,
                     makeCopyPathMessage(srcUri, dstUri, storePathS),
-                {storePathS, srcUri, dstUri});
+                    {storePathS, srcUri, dstUri}
+                );
                 PushActivity pact(act.id);
 
                 LambdaSink progressSink([&, total = 0ULL](std::string_view data) mutable {
                     total += data.size();
                     act.progress(total, info->narSize);
                 });
-            TeeSink tee { sink, progressSink };
+                TeeSink tee{sink, progressSink};
 
                 srcStore.narFromPath(missingPath, tee);
             });

src/libutil/logging.cc

@@ -26,8 +26,6 @@ void setCurActivity(const ActivityId activityId)
     curActivity = activityId;
 }
 
-Logger * logger = makeSimpleLogger(true);
-
 void Logger::warn(const std::string & msg)
 {
     log(lvlWarn, ANSI_WARNING "warning:" ANSI_NORMAL " " + msg);
@@ -108,6 +106,38 @@ public:
     }
 };
 
+// XXX: We have to leak this so that we can not destroy the damned thing on
+// shutdown because of destructor ordering. Bad evil horrible.
+LoggerWrapper &logger = *(new LoggerWrapper(makeSimpleLogger(true)));
+
+class NullLogger : public Logger
+{
+    void log(Verbosity lvl, std::string_view s) override {}
+
+    void logEI(const ErrorInfo & ei) override {}
+};
+
+Logger * globalNullLogger = new NullLogger();
+Logger * globalSimpleLogger = new SimpleLogger(false);
+
+[[gnu::destructor(65535)]]
+void switchToShutdownLogger()
+{
+    static auto dontDelete = [](auto d) {};
+
+    // XXX: Replace the logger with a global logger that is leaked at the end of the process
+    // This is so that custom loggers with meaningful destructors are guaranteed to actually be destroyed.
+    // Genuinely I am so sorry for this code.
+    //
+    // If there's a tty on the other end, we assume it's probably ok if the log
+    // format regresses to basic, and we consider it more important that the
+    // logs get out at all.
+    //
+    // FIXME: Replace this madness with explicitly passing around a shared
+    // pointer to const LoggerWrapper, because holy cow globals are broken.
+    logger.replace(std::shared_ptr<Logger>(isatty(STDERR_FILENO) ? globalSimpleLogger : globalNullLogger, dontDelete));
+}
+
 Verbosity verbosity = lvlInfo;
 
 void writeToStderr(std::string_view s)
@@ -122,18 +152,18 @@ void writeToStderr(std::string_view s)
     }
 }
 
-Logger * makeSimpleLogger(bool printBuildLogs)
+std::shared_ptr<Logger> makeSimpleLogger(bool printBuildLogs)
 {
-    return new SimpleLogger(printBuildLogs);
+    return std::make_shared<SimpleLogger>(printBuildLogs);
 }
 
 std::atomic<uint64_t> nextId{0};
 
-Activity::Activity(Logger & logger, Verbosity lvl, ActivityType type,
+Activity::Activity(std::shared_ptr<Logger> logger, Verbosity lvl, ActivityType type,
     const std::string & s, const Logger::Fields & fields, ActivityId parent)
     : logger(logger), id(nextId++ + (((uint64_t) getpid()) << 32))
 {
-    logger.startActivity(id, lvl, type, s, fields, parent);
+    logger->startActivity(id, lvl, type, s, fields, parent);
 }
 
 void to_json(nlohmann::json & json, std::shared_ptr<Pos> pos)
@@ -152,9 +182,9 @@ void to_json(nlohmann::json & json, std::shared_ptr<Pos> pos)
 }
 
 struct JSONLogger : Logger {
-    Logger & prevLogger;
+    std::shared_ptr<Logger> prevLogger;
 
-    JSONLogger(Logger & prevLogger) : prevLogger(prevLogger) { }
+    JSONLogger(std::shared_ptr<Logger> prevLogger) : prevLogger(prevLogger) { }
 
     bool isVerbose() override {
         return true;
@@ -175,7 +205,7 @@ struct JSONLogger : Logger {
 
     void write(const nlohmann::json & json)
     {
-        prevLogger.log(lvlError, "@nix " + json.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace));
+        prevLogger->log(lvlError, "@nix " + json.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace));
     }
 
     void log(Verbosity lvl, std::string_view s) override
@@ -247,9 +277,9 @@ struct JSONLogger : Logger {
     }
 };
 
-Logger * makeJSONLogger(Logger & prevLogger)
+std::shared_ptr<Logger> makeJSONLogger(std::shared_ptr<Logger> prevLogger)
 {
-    return new JSONLogger(prevLogger);
+    return std::make_shared<JSONLogger>(std::move(prevLogger));
 }
 
 static Logger::Fields getFields(nlohmann::json & json)
@@ -325,7 +355,7 @@ bool handleJSONLogMessage(const std::string & msg,
 Activity::~Activity()
 {
     try {
-        logger.stopActivity(id);
+        logger->stopActivity(id);
     } catch (...) {
         ignoreException();
     }

src/libutil/logging.hh

@@ -1,7 +1,6 @@
 #pragma once
 ///@file
 
-#include "types.hh"
 #include "error.hh"
 #include "config.hh"
 
@@ -132,14 +131,14 @@ void setCurActivity(const ActivityId activityId);
 
 struct Activity
 {
-    Logger & logger;
+    std::shared_ptr<Logger> logger;
 
     const ActivityId id;
 
-    Activity(Logger & logger, Verbosity lvl, ActivityType type, const std::string & s = "",
+    Activity(std::shared_ptr<Logger> logger, Verbosity lvl, ActivityType type, const std::string & s = "",
         const Logger::Fields & fields = {}, ActivityId parent = getCurActivity());
 
-    Activity(Logger & logger, ActivityType type,
+    Activity(std::shared_ptr<Logger> logger, ActivityType type,
         const Logger::Fields & fields = {}, ActivityId parent = getCurActivity())
         : Activity(logger, lvlError, type, "", fields, parent) { };
 
@@ -163,7 +162,7 @@ struct Activity
 
     void result(ResultType type, const Logger::Fields & fields) const
     {
-        logger.result(id, type, fields);
+        logger->result(id, type, fields);
     }
 
     friend class Logger;
@@ -176,11 +175,39 @@ struct PushActivity
     ~PushActivity() { setCurActivity(prevAct); }
 };
 
-extern Logger * logger;
+/** Wrapper to make replacing the global logger object thread-safe, since we do
+ * that in various places.
+ *
+ * The actual usage of shared_ptr across threads is ok, only replacing it is
+ * not thread safe.
+ */
+struct LoggerWrapper
+{
+    std::atomic<std::shared_ptr<Logger>> inner;
 
-Logger * makeSimpleLogger(bool printBuildLogs = true);
+    explicit LoggerWrapper(std::shared_ptr<Logger> inner) : inner(inner) {}
 
-Logger * makeJSONLogger(Logger & prevLogger);
+    const std::shared_ptr<Logger> operator->() const {
+        return inner.load(std::memory_order_relaxed);
+    }
+
+    const std::shared_ptr<Logger> operator*() const {
+        return inner.load(std::memory_order_relaxed);
+    }
+
+    /**
+     * Replaces the logger with a new one atomically.
+     */
+    const std::shared_ptr<Logger> replace(std::shared_ptr<Logger> newInner) {
+        return inner.exchange(std::move(newInner), std::memory_order_relaxed);
+    }
+};
+
+extern LoggerWrapper& logger;
+
+std::shared_ptr<Logger> makeSimpleLogger(bool printBuildLogs = true);
+
+std::shared_ptr<Logger> makeJSONLogger(std::shared_ptr<Logger> prevLogger);
 
 /**
  * suppress msgs > this

src/libutil/processes.cc

@@ -190,7 +190,7 @@ static int childEntry(void * arg)
 pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
 {
     std::function<void()> wrapper = [&]() {
-        logger = makeSimpleLogger();
+        logger.replace(makeSimpleLogger());
         try {
 #if __linux__
             if (options.dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1)

src/libutil/sync.hh

@@ -40,50 +40,96 @@ public:
     class Lock
     {
     private:
+        // Non-owning pointer. This would be an
+        // optional<reference_wrapper<Sync>> if it didn't break gdb accessing
+        // Lock values (as of 2024-06-15, gdb 14.2)
         Sync * s;
         std::unique_lock<M> lk;
         friend Sync;
-        Lock(Sync * s) : s(s), lk(s->mutex) { }
-    public:
-        Lock(Lock && l) : s(l.s) { abort(); }
-        Lock(const Lock & l) = delete;
-        ~Lock() { }
-        T * operator -> () { return &s->data; }
-        T & operator * () { return s->data; }
+        Lock(Sync &s) : s(&s), lk(s.mutex) { }
 
-        void wait(std::condition_variable & cv)
+        inline void checkLockingInvariants()
         {
             assert(s);
+            assert(lk.owns_lock());
+        }
+
+    public:
+        Lock(Lock && l) : s(l.s), lk(std::move(l.lk))
+        {
+            l.s = nullptr;
+        }
+
+        Lock(const Lock & l) = delete;
+
+        ~Lock() { }
+
+        T * operator -> ()
+        {
+            checkLockingInvariants();
+            return &s->data;
+        }
+
+        T & operator * ()
+        {
+            checkLockingInvariants();
+            return s->data;
+        }
+
+        /**
+         * Wait for the given condition variable with no timeout.
+         *
+         * May spuriously wake up.
+         */
+        void wait(std::condition_variable & cv)
+        {
+            checkLockingInvariants();
             cv.wait(lk);
         }
 
+        /**
+         * Wait for the given condition variable for a maximum elapsed time of \p duration.
+         *
+         * May spuriously wake up.
+         */
         template<class Rep, class Period>
         std::cv_status wait_for(std::condition_variable & cv,
             const std::chrono::duration<Rep, Period> & duration)
         {
-            assert(s);
+            checkLockingInvariants();
             return cv.wait_for(lk, duration);
         }
 
+        /**
+         * Wait for the given condition variable for a maximum elapsed time of \p duration.
+         * Calls \p pred to check if the wakeup should be heeded: \p pred
+         * returning false will ignore the wakeup.
+         */
         template<class Rep, class Period, class Predicate>
         bool wait_for(std::condition_variable & cv,
             const std::chrono::duration<Rep, Period> & duration,
             Predicate pred)
         {
-            assert(s);
+            checkLockingInvariants();
             return cv.wait_for(lk, duration, pred);
         }
 
+        /**
+         * Wait for the given condition variable or until the time point \p duration.
+         */
         template<class Clock, class Duration>
         std::cv_status wait_until(std::condition_variable & cv,
             const std::chrono::time_point<Clock, Duration> & duration)
         {
-            assert(s);
+            checkLockingInvariants();
             return cv.wait_until(lk, duration);
         }
     };
 
-    Lock lock() { return Lock(this); }
+    /**
+     * Lock this Sync and return a RAII guard object.
+     */
+    Lock lock() { return Lock(*this); }
 };
 
 }

tests/unit/libexpr/primops.cc

@@ -27,16 +27,15 @@ namespace nix {
     };
 
     class CaptureLogging {
-        Logger * oldLogger;
-        std::unique_ptr<CaptureLogger> tempLogger;
+        std::shared_ptr<Logger> oldLogger;
+        std::shared_ptr<CaptureLogger> tempLogger;
         public:
-            CaptureLogging() : tempLogger(std::make_unique<CaptureLogger>()) {
-                oldLogger = logger;
-                logger = tempLogger.get();
+            CaptureLogging() : tempLogger(std::make_shared<CaptureLogger>()) {
+                oldLogger = logger.replace(tempLogger);
             }
 
             ~CaptureLogging() {
-                logger = oldLogger;
+                logger.replace(oldLogger);
             }
 
             std::string get() const {