Method lock_shared

system/lib/libcxx/src/shared_mutex.cpp:50–57

// Shared ownership

void __shared_mutex_base::lock_shared() {
  unique_lock<mutex> lk(__mut_);
  while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_)
    __gate1_.wait(lk);
  unsigned num_readers = (__state_ & __n_readers_) + 1;
  __state_ &= ~__n_readers_;
  __state_ |= num_readers;
}

bool __shared_mutex_base::try_lock_shared() {
  unique_lock<mutex> lk(__mut_);