| 59 | } |
| 60 | |
| 61 | void write_unlock() |
| 62 | { |
| 63 | // NOTE: We need to satisfy the waiter(s) futures outside the |
| 64 | // critical section because it might trigger callbacks which |
| 65 | // try to reacquire a read or write lock. |
| 66 | std::queue<Waiter> unblocked; |
| 67 | |
| 68 | synchronized (data->lock) { |
| 69 | CHECK(data->write_locked); |
| 70 | CHECK_EQ(data->read_locked, 0u); |
| 71 | |
| 72 | data->write_locked = false; |
| 73 | |
| 74 | if (!data->waiters.empty()) { |
| 75 | switch (data->waiters.front().type) { |
| 76 | case Waiter::READ: |
| 77 | // Dequeue the group of readers at the front. |
| 78 | while (!data->waiters.empty() && |
| 79 | data->waiters.front().type == Waiter::READ) { |
| 80 | unblocked.push(std::move(data->waiters.front())); |
| 81 | data->waiters.pop(); |
| 82 | } |
| 83 | |
| 84 | data->read_locked = unblocked.size(); |
| 85 | |
| 86 | break; |
| 87 | |
| 88 | case Waiter::WRITE: |
| 89 | unblocked.push(std::move(data->waiters.front())); |
| 90 | data->waiters.pop(); |
| 91 | data->write_locked = true; |
| 92 | |
| 93 | CHECK_EQ(data->read_locked, 0u); |
| 94 | |
| 95 | break; |
| 96 | } |
| 97 | } |
| 98 | } |
| 99 | |
| 100 | while (!unblocked.empty()) { |
| 101 | unblocked.front().promise.set(Nothing()); |
| 102 | unblocked.pop(); |
| 103 | } |
| 104 | } |
| 105 | |
| 106 | // TODO(bmahler): Consider returning a 'Locked' object in the |
| 107 | // future as the mechanism for unlocking, rather than exposing |