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#include <mbgl/actor/mailbox.hpp>
#include <mbgl/actor/message.hpp>
#include <mbgl/actor/scheduler.hpp>
#include <cassert>
namespace mbgl {
Mailbox::Mailbox() = default;
Mailbox::Mailbox(Scheduler& scheduler_)
: scheduler(&scheduler_) {
}
void Mailbox::open(Scheduler& scheduler_) {
assert(!scheduler);
// As with close(), block until neither receive() nor push() are in progress, and acquire the two
// mutexes in the same order.
std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex);
std::lock_guard<std::mutex> pushingLock(pushingMutex);
scheduler = &scheduler_;
if (closed) {
return;
}
if (!queue.empty()) {
(*scheduler)->schedule(makeClosure(shared_from_this()));
}
}
void Mailbox::close() {
// Block until neither receive() nor push() are in progress. Two mutexes are used because receive()
// must not block send(). Of the two, the receiving mutex must be acquired first, because that is
// the order that an actor will obtain them when it self-sends a message, and consistent lock
// acquisition order prevents deadlocks.
// The receiving mutex is recursive to allow a mailbox (and thus the actor) to close itself.
std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex);
std::lock_guard<std::mutex> pushingLock(pushingMutex);
closed = true;
}
bool Mailbox::isOpen() const { return bool(scheduler); }
void Mailbox::push(std::unique_ptr<Message> message) {
std::lock_guard<std::mutex> pushingLock(pushingMutex);
if (closed) {
return;
}
std::lock_guard<std::mutex> queueLock(queueMutex);
bool wasEmpty = queue.empty();
queue.push(std::move(message));
if (wasEmpty && scheduler) {
(*scheduler)->schedule(makeClosure(shared_from_this()));
}
}
void Mailbox::receive() {
std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex);
assert(scheduler);
if (closed) {
return;
}
std::unique_ptr<Message> message;
bool wasEmpty;
{
std::lock_guard<std::mutex> queueLock(queueMutex);
assert(!queue.empty());
message = std::move(queue.front());
queue.pop();
wasEmpty = queue.empty();
}
(*message)();
if (!wasEmpty) {
(*scheduler)->schedule(makeClosure(shared_from_this()));
}
}
// static
void Mailbox::maybeReceive(std::weak_ptr<Mailbox> mailbox) {
if (auto locked = mailbox.lock()) {
locked->receive();
}
}
// static
std::function<void()> Mailbox::makeClosure(std::weak_ptr<Mailbox> mailbox) {
return [mailbox]() { maybeReceive(mailbox); };
}
} // namespace mbgl
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