Function test_cache_erase_parallel

src/test/cuckoocache_tests.cpp:198–277

template <typename Cache>
static void test_cache_erase_parallel(size_t megabytes)
{
    double load = 1;
    local_rand_ctx = FastRandomContext(true);
    std::vector<uint256> hashes;
    Cache set{};
    size_t bytes = megabytes * (1 << 20);
    set.setup_bytes(bytes);
    uint32_t n_insert = static_cast<uint32_t>(load * (bytes / sizeof(uint256)));
    hashes.resize(n_insert);
    for (uint32_t i = 0; i < n_insert; ++i) {
        uint32_t* ptr = (uint32_t*)hashes[i].begin();
        for (uint8_t j = 0; j < 8; ++j)
            *(ptr++) = local_rand_ctx.rand32();
    }
    /** We make a copy of the hashes because future optimizations of the
     * cuckoocache may overwrite the inserted element, so the test is
     * "future proofed".
     */
    std::vector<uint256> hashes_insert_copy = hashes;
    boost::shared_mutex mtx;

    {
        /** Grab lock to make sure we release inserts */
        boost::unique_lock<boost::shared_mutex> l(mtx);
        /** Insert the first half */
        for (uint32_t i = 0; i < (n_insert / 2); ++i)
            set.insert(hashes_insert_copy[i]);
    }

    /** Spin up 3 threads to run contains with erase.
     */
    std::vector<std::thread> threads;
    /** Erase the first quarter */
    for (uint32_t x = 0; x < 3; ++x)
        /** Each thread is emplaced with x copy-by-value
        */
        threads.emplace_back([&, x] {
            boost::shared_lock<boost::shared_mutex> l(mtx);
            size_t ntodo = (n_insert/4)/3;
            size_t start = ntodo*x;
            size_t end = ntodo*(x+1);
            for (uint32_t i = start; i < end; ++i)
                set.contains(hashes[i], true);
        });

    /** Wait for all threads to finish
     */
    for (std::thread& t : threads)
        t.join();
    /** Grab lock to make sure we observe erases */
    boost::unique_lock<boost::shared_mutex> l(mtx);
    /** Insert the second half */
    for (uint32_t i = (n_insert / 2); i < n_insert; ++i)
        set.insert(hashes_insert_copy[i]);

    /** elements that we marked erased but that are still there */
    size_t count_erased_but_contained = 0;