bitvec::atomic_set (#227)

include/cista/containers/bitvec.h

@@ -88,6 +88,32 @@ struct basic_bitvec {
  }
  }
 
+#if __has_cpp_attribute(__cpp_lib_atomic_ref)
+ constexpr void atomic_set(
+ Key const i, bool const val = true,
+ memory_order succ = std::memory_order::memory_order_seq_cst,
+ memory_order fail = std::memory_order::memory_order_seq_cst) noexcept {
+ assert(i < size_);
+ assert((to_idx(i) / bits_per_block) < blocks_.size());
+ auto const block = std::atomic_ref{
+ blocks_[static_cast<size_type>(to_idx(i)) / bits_per_block]};
+ auto const bit = to_idx(i) % bits_per_block;
+
+ auto const update_block = [&](block_t const b) -> block_t {
+ if (val) {
+ return block | (block_t{1U} << bit);
+ } else {
+ return block & (~block_t{0U} ^ (block_t{1U} << bit));
+ }
+ };
+
+ auto expected = block.load();
+ while (std::atomic_compare_exchange_weak(
+ &block, &expected, update_block(expected), succ, fail)) {
+ }
+ }
+#endif
+
  void reset() noexcept { blocks_ = {}; }
 
  bool operator[](Key const i) const noexcept { return test(i); }

test/bitvec_test.cc

@@ -105,6 +105,37 @@ unsigned long get_random_number() { // period 2^96-1
  return z;
 }
 
+#if __has_cpp_attribute(__cpp_lib_atomic_ref)
+TEST_CASE("bitvec atomic set") {
+ constexpr auto const kBits = 100'000U;
+ constexpr auto const kWorkers = 100U;
+
+ auto start = std::atomic_bool{};
+ auto b = cista::raw::bitvec{};
+ b.resize(kBits);
+ auto workers = std::vector<std::thread>(kWorkers);
+ for (auto i = 0U; i != kWorkers; ++i) {
+ workers[i] = std::thread{[&, i]() {
+ while (!start) {
+ // wait for synchronized start
+ }
+
+ for (auto j = i; j < kBits; j += kBits / kWorkers) {
+ b.atomic_set(j);
+ }
+ }};
+ }
+
+ start.store(true);
+
+ for (auto& w : workers) {
+ w.join();
+ }
+
+ CHECK(b.count() == kBits);
+}
+#endif
+
 TEST_CASE("bitvec parallel") {
  constexpr auto const kBits = 1'000'000U;
  constexpr auto const kWorkers = 100U;