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Busy waiting added

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This commit is contained in:
Nekotekina 2017-02-15 18:07:42 +03:00
parent b637bd3866
commit b1aa87b515
7 changed files with 196 additions and 373 deletions
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161
Utilities/sema.cpp
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@ -1,50 +1,59 @@
#include "sema.h"
#include "sync.h"
void semaphore_base::imp_wait(bool lsb)
void semaphore_base::imp_wait()
{
// 1. Obtain LSB, reset it
// 2. Notify other posters if necessary
for (int i = 0; i < 10; i++)
{
busy_wait();
const s32 value = m_value.load();
if (value > 0 && m_value.compare_and_swap_test(value, value - 1))
{
return;
}
}
#ifdef _WIN32
if (!lsb)
{
while ((m_value & 1) == 0 || !atomic_storage<s32>::btr(m_value.raw(), 0))
{
// Wait infinitely until signaled
verify(HERE), NtWaitForKeyedEvent(nullptr, &m_value, false, nullptr) == ERROR_SUCCESS;
}
}
const s32 value = m_value.fetch_sub(1);
// Notify instantly
LARGE_INTEGER timeout;
timeout.QuadPart = 0;
if (HRESULT rc = NtReleaseKeyedEvent(nullptr, (u8*)&m_value + 2, false, &timeout))
if (value <= 0)
{
verify(HERE), rc == WAIT_TIMEOUT;
NtWaitForKeyedEvent(nullptr, &m_value, false, nullptr);
}
#elif __linux__
if (!lsb)
{
for (s32 value = m_value; (m_value & 1) == 0 || !atomic_storage<s32>::btr(m_value.raw(), 0); value = m_value)
{
if (futex(&m_value.raw(), FUTEX_WAIT_BITSET_PRIVATE, value, nullptr, nullptr, -2) == -1)
{
verify(HERE), errno == EAGAIN;
}
}
}
verify(HERE), futex(&m_value.raw(), FUTEX_WAKE_BITSET_PRIVATE, 1, nullptr, nullptr, 1) >= 0;
#else
if (lsb)
while (true)
{
return;
}
// Try hard way
const s32 value = m_value.op_fetch([](s32& value)
{
// Use sign bit to acknowledge waiter presence
if (value && value > INT32_MIN)
{
value--;
while ((m_value & 1) == 0 || !atomic_storage<s32>::btr(m_value.raw(), 0))
{
std::this_thread::sleep_for(std::chrono::microseconds(50));
if (value < 0)
{
// Remove sign bit
value -= INT32_MIN;
}
}
else
{
// Set sign bit
value = INT32_MIN;
}
});
if (value >= 0)
{
// Signal other waiter to wake up or to restore sign bit
futex(&m_value.raw(), FUTEX_WAKE_PRIVATE, 1, nullptr, nullptr, 0);
return;
}
futex(&m_value.raw(), FUTEX_WAIT_PRIVATE, value, nullptr, nullptr, 0);
}
#endif
}
@ -53,62 +62,10 @@ void semaphore_base::imp_post(s32 _old)
{
verify("semaphore_base: overflow" HERE), _old < 0;
// 1. Set LSB, waiting until it can be set if necessary
// 2. Notify waiter
#ifdef _WIN32
while ((_old & 1) == 0 && atomic_storage<s32>::bts(m_value.raw(), 0))
{
static_assert(ERROR_SUCCESS == 0, "Unexpected ERROR_SUCCESS value");
LARGE_INTEGER timeout;
timeout.QuadPart = -500; // ~50us
if (HRESULT rc = NtWaitForKeyedEvent(nullptr, (u8*)&m_value + 2, false, &timeout))
{
verify(HERE), rc == WAIT_TIMEOUT;
}
}
LARGE_INTEGER timeout;
timeout.QuadPart = 0; // Instant for the first attempt
while (HRESULT rc = NtReleaseKeyedEvent(nullptr, &m_value, false, &timeout))
{
verify(HERE), rc == WAIT_TIMEOUT;
if (!timeout.QuadPart)
{
timeout.QuadPart = -500; // ~50us
NtDelayExecution(false, &timeout);
}
if ((m_value & 1) == 0)
{
break;
}
}
#elif __linux__
for (s32 value = m_value; (_old & 1) == 0 && atomic_storage<s32>::bts(m_value.raw(), 0); value = m_value)
{
if (futex(&m_value.raw(), FUTEX_WAIT_BITSET_PRIVATE, value, nullptr, nullptr, 1) == -1)
{
verify(HERE), errno == EAGAIN;
}
}
if (1 + 0 == verify(HERE, 1 + futex(&m_value.raw(), FUTEX_WAKE_BITSET_PRIVATE, 1, nullptr, nullptr, -2)))
{
usleep(50);
}
NtReleaseKeyedEvent(nullptr, &m_value, false, nullptr);
#else
if (_old & 1)
{
return;
}
while (m_value & 1 || atomic_storage<s32>::bts(m_value.raw(), 0))
{
std::this_thread::sleep_for(std::chrono::microseconds(50));
}
futex(&m_value.raw(), FUTEX_WAKE_PRIVATE, 1, nullptr, nullptr, 0);
#endif
}
@ -117,24 +74,13 @@ bool semaphore_base::try_wait()
// Conditional decrement
const s32 value = m_value.fetch_op([](s32& value)
{
if (value > 0 || value & 1)
if (value > 0)
{
if (value <= 1)
{
value &= ~1;
}
value -= 1 << 1;
value -= 1;
}
});
if (value & 1 && value <= 1)
{
imp_wait(true);
return true;
}
return value > 0 || value & 1;
return value > 0;
}
bool semaphore_base::try_post(s32 _max)
@ -144,18 +90,13 @@ bool semaphore_base::try_post(s32 _max)
{
if (value < _max)
{
if (value < 0)
{
value |= 1;
}
value += 1 << 1;
value += 1;
}
});
if (value < 0)
{
imp_post(value ^ 1);
imp_post(value);
}
return value < _max;