tree-wide: unify progress bar inactive and paused states

Previously, the progress bar had two subtly different states in which the bar
would not actually render, both with their own shortcomings: inactive (which
was irreversible) and paused (reversible, but swallowing logs). Furthermore,
there was no way of resetting the statistics, so a very bad solution was
implemented (243c0f18da) that would create a new
logger for each line of the repl, leaking the previous one and discarding the
value of printBuildLogs. Finally, if stderr was not attached to a TTY, the
update thread was started even though the logger was not active, violating the
invariant required by the destructor (which is not observed because the logger
is leaked).

In this commit, the two aforementioned states are unified into a single one,
which can be exited again, correctly upholds the invariant that the update
thread is only running while the progress bar is active, and does not swallow
logs. The latter change in behavior is not expected to be a problems in the
rare cases where the paused state was used before, since other loggers (like
the simple one) don't exhibit it anyway. The startProgressBar/stopProgressBar
API is removed due to being a footgun, and a new method for properly resetting
the progress is added.

Co-Authored-By: Qyriad <qyriad@qyriad.me>
Change-Id: I2b7c3eb17d439cd0c16f7b896cfb61239ac7ff3a

src/libcmd/repl.cc

@@ -32,7 +32,6 @@
 #include "local-fs-store.hh"
 #include "signals.hh"
 #include "print.hh"
-#include "progress-bar.hh"
 #include "gc-small-vector.hh"
 #include "users.hh"
 
@@ -300,7 +299,7 @@ ReplExitStatus NixRepl::mainLoop()
 
     /* Stop the progress bar because it interferes with the display of
        the repl. */
-    stopProgressBar();
+    logger->pause();
 
     std::string input;
 
@@ -684,9 +683,10 @@ ProcessLineResult NixRepl::processLine(std::string line)
             // TODO: this only shows a progress bar for explicitly initiated builds,
             // not eval-time fetching or builds performed for IFD.
             // But we can't just show it everywhere, since that would erase partial output from evaluation.
-            startProgressBar();
+            logger->resetProgress();
+            logger->resume();
             Finally stopLogger([&]() {
-                stopProgressBar();
+                logger->pause();
             });
 
             state->store->buildPaths({

src/libfetchers/git.cc

@@ -403,11 +403,8 @@ struct GitInputScheme : InputScheme
                 AutoDelete const _delete{msgPath};
                 writeFile(msgPath, *commitMsg);
 
-                // Pause the logger to allow for user input (such as a gpg passphrase) in `git commit`
-                logger->pause();
-                Finally restoreLogger([]() { logger->resume(); });
                 runProgram("git", true,
-                    { "-C", *root, "--git-dir", gitDir, "commit", std::string(path.rel()), "-F", msgPath });
+                    { "-C", *root, "--git-dir", gitDir, "commit", std::string(path.rel()), "-F", msgPath }, true);
             }
         }
     }

src/libmain/progress-bar.cc

@@ -4,7 +4,6 @@
 #include "names.hh"
 #include "terminal.hh"
 
-#include <atomic>
 #include <map>
 #include <thread>
 #include <sstream>
@@ -44,50 +43,56 @@ static std::string_view storePathToName(std::string_view path)
 ProgressBar::ProgressBar(bool isTTY)
     : isTTY(isTTY)
 {
-    state_.lock()->active = isTTY;
-    updateThread = std::thread([&]() {
-        auto state(state_.lock());
-        auto nextWakeup = A_LONG_TIME;
-        while (state->active) {
-            if (!state->haveUpdate)
-                state.wait_for(updateCV, nextWakeup);
-            nextWakeup = draw(*state, {});
-            state.wait_for(quitCV, std::chrono::milliseconds(50));
-        }
-    });
+    resume();
 }
 
 ProgressBar::~ProgressBar()
 {
-    stop();
+    pause();
 }
 
-/* Called by destructor, can't be overridden */
-void ProgressBar::stop()
+void ProgressBar::pause()
 {
+    if (!isTTY) return;
     {
         auto state(state_.lock());
-        if (!state->active) return;
-        state->active = false;
-        writeToStderr("\r\e[K");
+        state->paused++;
+        if (state->paused > 1) return; // recursive pause, the update thread is already gone
         updateCV.notify_one();
         quitCV.notify_one();
     }
     updateThread.join();
 }
 
-void ProgressBar::pause()
+void ProgressBar::resetProgress()
 {
-    state_.lock()->paused = true;
-    writeToStderr("\r\e[K");
+    auto state(state_.lock());
+    auto prevPaused = state->paused;
+    *state = ProgressBar::State {
+        .paused = prevPaused,
+    };
+    update(*state);
 }
 
 void ProgressBar::resume()
 {
-    state_.lock()->paused = false;
+    if (!isTTY) return;
+    auto state(state_.lock());
+    assert(state->paused > 0); // should be paused
+    state->paused--;
+    if (state->paused > 0) return; // recursive pause, wait for the parents to resume too
+    state->haveUpdate = true;
+    updateThread = std::thread([&]() {
+        auto state(state_.lock());
+        auto nextWakeup = A_LONG_TIME;
+        while (state->paused == 0) {
+            if (!state->haveUpdate)
+                state.wait_for(updateCV, nextWakeup);
+            nextWakeup = draw(*state, {});
+            state.wait_for(quitCV, std::chrono::milliseconds(50));
+        }
         writeToStderr("\r\e[K");
-    state_.lock()->haveUpdate = true;
-    updateCV.notify_one();
+    });
 }
 
 bool ProgressBar::isVerbose()
@@ -114,7 +119,7 @@ void ProgressBar::logEI(const ErrorInfo & ei)
 
 void ProgressBar::log(State & state, Verbosity lvl, std::string_view s)
 {
-    if (state.active) {
+    if (state.paused == 0) {
         draw(state, s);
     } else {
         auto s2 = s + ANSI_NORMAL "\n";
@@ -318,7 +323,7 @@ std::chrono::milliseconds ProgressBar::draw(State & state, const std::optional<s
     auto nextWakeup = A_LONG_TIME;
 
     state.haveUpdate = false;
-    if (state.paused || !state.active) return nextWakeup;
+    if (state.paused > 0) return nextWakeup;
 
     auto windowSize = getWindowSize();
     auto width = windowSize.second;
@@ -525,7 +530,7 @@ std::string ProgressBar::getStatus(State & state)
 void ProgressBar::writeToStdout(std::string_view s)
 {
     auto state(state_.lock());
-    if (state->active) {
+    if (state->paused == 0) {
         Logger::writeToStdout(s);
         draw(*state, {});
     } else {
@@ -536,7 +541,7 @@ void ProgressBar::writeToStdout(std::string_view s)
 std::optional<char> ProgressBar::ask(std::string_view msg)
 {
     auto state(state_.lock());
-    if (!state->active || !isatty(STDIN_FILENO)) return {};
+    if (state->paused > 0 || !isatty(STDIN_FILENO)) return {};
     std::cerr << fmt("\r\e[K%s ", msg);
     auto s = trim(readLine(STDIN_FILENO));
     if (s.size() != 1) return {};
@@ -559,16 +564,4 @@ Logger * makeProgressBar()
     return new ProgressBar(shouldANSI());
 }
 
-void startProgressBar()
-{
-    logger = makeProgressBar();
-}
-
-void stopProgressBar()
-{
-    auto progressBar = dynamic_cast<ProgressBar *>(logger);
-    if (progressBar) progressBar->stop();
-
-}
-
 }

src/libmain/progress-bar.hh

@@ -48,9 +48,8 @@ struct ProgressBar : public Logger
 
         uint64_t corruptedPaths = 0, untrustedPaths = 0;
 
-        bool active = true;
-        bool paused = false;
-        bool haveUpdate = true;
+        uint32_t paused = 1;
+        bool haveUpdate = false;
     };
 
     Sync<State> state_;
@@ -67,10 +66,10 @@ struct ProgressBar : public Logger
 
     ~ProgressBar();
 
-    void stop() override final;
-
     void pause() override;
 
+    void resetProgress() override;
+
     void resume() override;
 
     bool isVerbose() override;
@@ -113,8 +112,4 @@ struct ProgressBar : public Logger
 
 Logger * makeProgressBar();
 
-void startProgressBar();
-
-void stopProgressBar();
-
 }

src/libmain/shared.cc

@@ -4,7 +4,6 @@
 #include "gc-store.hh"
 #include "signals.hh"
 #include "loggers.hh"
-#include "progress-bar.hh"
 #include "current-process.hh"
 
 #include <algorithm>
@@ -349,7 +348,7 @@ RunPager::RunPager()
     if (!pager) pager = getenv("PAGER");
     if (pager && ((std::string) pager == "" || (std::string) pager == "cat")) return;
 
-    stopProgressBar();
+    logger->pause();
 
     Pipe toPager;
     toPager.create();

src/libutil/logging.hh

@@ -117,9 +117,8 @@ public:
 
     virtual ~Logger() { }
 
-    virtual void stop() { };
-
     virtual void pause() { };
+    virtual void resetProgress() { };
     virtual void resume() { };
 
     // Whether the logger prints the whole build log

src/nix-build/nix-build.cc

@@ -543,7 +543,7 @@ static void main_nix_build(int argc, char * * argv)
 
         restoreProcessContext();
 
-        logger->stop();
+        logger->pause();
 
         execvp(shell->c_str(), argPtrs.data());
 
@@ -606,7 +606,7 @@ static void main_nix_build(int argc, char * * argv)
             outPaths.push_back(outputPath);
         }
 
-        logger->stop();
+        logger->pause();
 
         for (auto & path : outPaths)
             std::cout << store->printStorePath(path) << '\n';

src/nix/build.cc

@@ -3,7 +3,6 @@
 #include "shared.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"
-#include "progress-bar.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -143,7 +142,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                 createOutLinks(outLink, buildables, *store2);
 
         if (printOutputPaths) {
-            stopProgressBar();
+            logger->pause();
             for (auto & buildable : buildables) {
                 std::visit(overloaded {
                     [&](const BuiltPath::Opaque & bo) {

src/nix/cat.cc

@@ -2,7 +2,6 @@
 #include "store-api.hh"
 #include "fs-accessor.hh"
 #include "nar-accessor.hh"
-#include "progress-bar.hh"
 
 using namespace nix;
 
@@ -20,7 +19,7 @@ struct MixCat : virtual Args
 
         auto file = accessor->readFile(path);
 
-        stopProgressBar();
+        logger->pause();
         writeFull(STDOUT_FILENO, file);
     }
 };

src/nix/develop.cc

@@ -6,7 +6,6 @@
 #include "store-api.hh"
 #include "outputs-spec.hh"
 #include "derivations.hh"
-#include "progress-bar.hh"
 #include "run.hh"
 
 #include <iterator>
@@ -690,7 +689,7 @@ struct CmdPrintDevEnv : Common, MixJSON
     {
         auto buildEnvironment = getBuildEnvironment(store, installable).first;
 
-        stopProgressBar();
+        logger->pause();
 
         if (json) {
             logger->writeToStdout(buildEnvironment.toJSON());

src/nix/dump-path.cc

@@ -1,7 +1,6 @@
 #include "command.hh"
 #include "store-api.hh"
 #include "archive.hh"
-#include "progress-bar.hh"
 
 using namespace nix;
 
@@ -21,7 +20,7 @@ struct CmdDumpPath : StorePathCommand
 
     void run(ref<Store> store, const StorePath & storePath) override
     {
-        stopProgressBar();
+        logger->pause();
         FdSink sink(STDOUT_FILENO);
         store->narFromPath(storePath, sink);
         sink.flush();
@@ -57,7 +56,7 @@ struct CmdDumpPath2 : Command
 
     void run() override
     {
-        stopProgressBar();
+        logger->pause();
         FdSink sink(STDOUT_FILENO);
         dumpPath(path, sink);
         sink.flush();

src/nix/edit.cc

@@ -2,7 +2,6 @@
 #include "shared.hh"
 #include "eval.hh"
 #include "attr-path.hh"
-#include "progress-bar.hh"
 #include "editor-for.hh"
 #include "current-process.hh"
 
@@ -42,7 +41,7 @@ struct CmdEdit : InstallableCommand
             }
         }();
 
-        stopProgressBar();
+        logger->pause();
 
         auto args = editorFor(file, line);
 

src/nix/eval.cc

@@ -6,7 +6,6 @@
 #include "eval.hh"
 #include "eval-inline.hh"
 #include "value-to-json.hh"
-#include "progress-bar.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -76,7 +75,7 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
         }
 
         if (writeTo) {
-            stopProgressBar();
+            logger->pause();
 
             if (pathExists(*writeTo))
                 throw Error("path '%s' already exists", *writeTo);
@@ -114,7 +113,7 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
         }
 
         else if (raw) {
-            stopProgressBar();
+            logger->pause();
             writeFull(STDOUT_FILENO, *state->coerceToString(noPos, *v, context, "while generating the eval command output"));
         }
 

src/nix/log.cc

@@ -3,7 +3,6 @@
 #include "shared.hh"
 #include "store-api.hh"
 #include "log-store.hh"
-#include "progress-bar.hh"
 
 using namespace nix;
 
@@ -55,7 +54,7 @@ struct CmdLog : InstallableCommand
 
             auto log = logSub.getBuildLog(path);
             if (!log) continue;
-            stopProgressBar();
+            logger->pause();
             printInfo("got build log for '%s' from '%s'", installable->what(), logSub.getUri());
             writeFull(STDOUT_FILENO, *log);
             return;

src/nix/main.cc

@@ -346,8 +346,6 @@ void mainWrapped(int argc, char * * argv)
     }
     #endif
 
-    Finally f([] { logger->stop(); });
-
     programPath = argv[0];
     auto programName = std::string(baseNameOf(programPath));
 
@@ -363,7 +361,8 @@ void mainWrapped(int argc, char * * argv)
 
     evalSettings.pureEval = true;
 
-    setLogFormat("bar");
+    setLogFormat(LogFormat::bar);
+    Finally f([] { logger->pause(); });
     settings.verboseBuild = false;
     if (isatty(STDERR_FILENO)) {
         verbosity = lvlNotice;

src/nix/prefetch.cc

@@ -1,10 +1,10 @@
 #include "command.hh"
 #include "common-args.hh"
+#include "loggers.hh"
 #include "shared.hh"
 #include "store-api.hh"
 #include "filetransfer.hh"
 #include "finally.hh"
-#include "progress-bar.hh"
 #include "tarfile.hh"
 #include "attr-path.hh"
 #include "eval-inline.hh"
@@ -180,10 +180,8 @@ static int main_nix_prefetch_url(int argc, char * * argv)
         if (args.size() > 2)
             throw UsageError("too many arguments");
 
-        Finally f([]() { stopProgressBar(); });
-
         if (isatty(STDERR_FILENO))
-          startProgressBar();
+            setLogFormat(LogFormat::bar);
 
         auto store = openStore();
         auto state = std::make_unique<EvalState>(myArgs.searchPath, store);
@@ -237,7 +235,7 @@ static int main_nix_prefetch_url(int argc, char * * argv)
         auto [storePath, hash] = prefetchFile(
             store, resolveMirrorUrl(*state, url), name, ht, expectedHash, unpack, executable);
 
-        stopProgressBar();
+        logger->pause();
 
         if (!printPath)
             printInfo("path is '%s'", store->printStorePath(storePath));

src/nix/run.cc

@@ -8,7 +8,6 @@
 #include "local-store.hh"
 #include "finally.hh"
 #include "fs-accessor.hh"
-#include "progress-bar.hh"
 #include "eval.hh"
 #include "build/personality.hh"
 #include "current-process.hh"
@@ -31,7 +30,7 @@ void runProgramInStore(ref<Store> store,
     const Strings & args,
     std::optional<std::string_view> system)
 {
-    stopProgressBar();
+    logger->pause();
 
     restoreProcessContext();
 

src/nix/sigs.cc

@@ -3,7 +3,6 @@
 #include "store-api.hh"
 #include "thread-pool.hh"
 #include "signals.hh"
-#include "progress-bar.hh"
 
 #include <atomic>
 
@@ -222,7 +221,7 @@ struct CmdKey : NixMultiCommand
         if (!command)
             throw UsageError("'nix key' requires a sub-command.");
 
-        stopProgressBar();
+        logger->pause();
         command->second->run();
     }
 };

src/nix/upgrade-nix.cc

@@ -13,7 +13,6 @@
 #include "eval-settings.hh"
 #include "attr-path.hh"
 #include "names.hh"
-#include "progress-bar.hh"
 
 using namespace nix;
 
@@ -88,7 +87,7 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
         auto version = DrvName(storePath.name()).version;
 
         if (dryRun) {
-            stopProgressBar();
+            logger->pause();
             warn("would upgrade to version %s", version);
             return;
         }
@@ -106,7 +105,7 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
                 throw Error("could not verify that '%s' works", program);
         }
 
-        stopProgressBar();
+        logger->pause();
 
         auto const fullStorePath = store->printStorePath(storePath);
 

src/nix/why-depends.cc

@@ -1,6 +1,5 @@
 #include "command.hh"
 #include "store-api.hh"
-#include "progress-bar.hh"
 #include "fs-accessor.hh"
 #include "shared.hh"
 
@@ -110,7 +109,7 @@ struct CmdWhyDepends : SourceExprCommand, MixOperateOnOptions
         auto dependencyPath = *optDependencyPath;
         auto dependencyPathHash = dependencyPath.hashPart();
 
-        stopProgressBar(); // FIXME
+        logger->pause(); // FIXME
 
         auto accessor = store->getFSAccessor();
 

tests/unit/libmain/progress-bar.cc

@@ -2,6 +2,7 @@
 
 #include "eval.hh"
 #include "progress-bar.hh"
+#include "loggers.hh"
 #include "logging.hh"
 #include "shared.hh"
 
@@ -23,7 +24,7 @@ namespace nix
         initNix();
         initGC();
 
-        startProgressBar();
+        setLogFormat(LogFormat::bar);
         ASSERT_NE(dynamic_cast<ProgressBar *>(logger), nullptr);
         ProgressBar & progressBar = dynamic_cast<ProgressBar &>(*logger);