void shared_mutex::imp_lock_shared(u32 val)
{
verify("shared_mutex underflow" HERE), val < c_err;
for (int i = 0; i < 10; i++)
{
busy_wait();
if (try_lock_shared())
{
return;
}
}
// Acquire writer lock and downgrade
const u32 old = m_value.fetch_add(c_one);
if (old == 0)
{
lock_downgrade();
return;
}
verify("shared_mutex overflow" HERE), (old % c_sig) + c_one < c_sig;
imp_wait();
lock_downgrade();
}
void lock_shared() noexcept {
for (;;) {
if (try_lock_shared()) {
return;
}
uintreg value;
do {
value = _bits.load(std::memory_order_acquire);
} while ((value & WRITER) != 0);
}
}
void shared_mutex_t::lock_shared()
{
if (!try_lock_shared())
{
std::unique_lock<std::mutex> lock(m_mutex);
m_wrcv.wait(lock, WRAP_EXPR(m_info.atomic_op([](ownership_info_t& info) -> bool
{
if (info.waiting_readers < UINT16_MAX)
{
info.waiting_readers++;
return true;
}
return false;
})));
m_rcv.wait(lock, WRAP_EXPR(m_info.atomic_op([](ownership_info_t& info) -> bool
{
if (!info.writers && !info.waiting_writers && info.readers < MAX_READERS)
{
info.readers++;
return true;
}
return false;
})));
const auto info = m_info.atomic_op([](ownership_info_t& info)
{
if (!info.waiting_readers--)
{
throw EXCEPTION("Invalid value");
}
});
if (info.waiting_readers == UINT16_MAX)
{
m_wrcv.notify_one();
}
}
}
