Crafter.Build/tests/ConcurrentCacheRace/main.cpp

#include <stdlib.h>
import std;
import Crafter.Build;
namespace fs = std::filesystem;
using namespace Crafter;

// Regression for the host-cache write race: when several crafter-build
// invocations shared the same XDG_CACHE_HOME, two LoadProject() calls would
// clobber each other's writes to `<cache>/<target>-<march>/std.pcm` and the
// `Crafter.Build-*.pcm` host modules. The loser's clang would then read a
// torn file via -fprebuilt-module-path and die with "malformed or corrupted
// precompiled file: 'can't skip to bit X from Y'". The fix routes every PCM
// write through a per-process temp + atomic rename so a reader always sees
// either the old or the new file, never a half-written one.
//
// LoadProject() is the right surface to test because it runs the full host
// bootstrap (BuildStdPcm + EnsureCrafterBuildPcms × the Crafter.Build-*
// modules), giving every concurrent thread enough writing-to-the-same-paths
// time for the race to surface. A pure BuildStdPcm test wouldn't — the std
// PCM write is too short to overlap reliably between threads.
namespace {
    fs::path FindCrafterBuildHome() {
        if (const char* env = std::getenv("CRAFTER_BUILD_HOME"); env && *env) {
            return env;
        }
        for (const char* candidate : {
            "/usr/local/share/crafter-build",
            "/usr/share/crafter-build",
        }) {
            if (fs::exists(fs::path(candidate) / "Crafter.Build.cppm")) {
                return candidate;
            }
        }
        return {};
    }

    void WriteFile(const fs::path& p, std::string_view contents) {
        std::ofstream out(p);
        out << contents;
    }
}

int main() {
    fs::path home = FindCrafterBuildHome();
    if (home.empty()) {
        std::println(std::cerr,
            "SKIP: no installed share/crafter-build found and CRAFTER_BUILD_HOME unset");
        return 77;
    }
    setenv("CRAFTER_BUILD_HOME", home.string().c_str(), 1);

    fs::path scratch = fs::temp_directory_path() / "crafter-build-concurrent-cache-race";
    std::error_code ec;
    fs::remove_all(scratch, ec);
    fs::create_directories(scratch);

    // Cold scratch cache. setenv before any thread starts so every thread's
    // GetCacheDir() call sees the same override.
    fs::path cacheDir = scratch / "cache";
    fs::create_directories(cacheDir);
    setenv("XDG_CACHE_HOME", cacheDir.string().c_str(), 1);

    constexpr int N = 4;
    std::vector<fs::path> projects;
    for (int i = 0; i < N; ++i) {
        fs::path dir = scratch / std::format("p{}", i);
        fs::create_directories(dir);
        WriteFile(dir / "project.cpp", std::format(
            "import std;\n"
            "import Crafter.Build;\n"
            "namespace fs = std::filesystem;\n"
            "using namespace Crafter;\n"
            "extern \"C\" Configuration CrafterBuildProject(std::span<const std::string_view>) {{\n"
            "    Configuration cfg;\n"
            "    cfg.path = \"./\";\n"
            "    cfg.name = \"p{}\";\n"
            "    cfg.outputName = \"p{}\";\n"
            "    cfg.target = HostTarget();\n"
            "    cfg.type = ConfigurationType::Executable;\n"
            "    return cfg;\n"
            "}}\n", i, i));
        projects.push_back(dir / "project.cpp");
    }

    std::array<std::string, N> errors;
    std::vector<std::thread> threads;
    threads.reserve(N);
    for (int i = 0; i < N; ++i) {
        threads.emplace_back([&, i]() {
            try {
                std::array<std::string_view, 0> args = {};
                (void)LoadProject(projects[i], args);
            } catch (const std::exception& e) {
                errors[i] = e.what();
            }
        });
    }
    for (std::thread& t : threads) t.join();

    int failures = 0;
    for (int i = 0; i < N; ++i) {
        if (!errors[i].empty()) {
            std::println(std::cerr, "FAIL p{}: {}", i, errors[i]);
            ++failures;
        }
    }

    fs::remove_all(scratch, ec);

    if (failures > 0) {
        std::println(std::cerr,
            "{}/{} concurrent LoadProject() invocations failed (host-cache race)",
            failures, N);
        return 1;
    }
    return 0;
}