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#pragma once
#include "defs.h"
#include <library/cpp/actors/util/futex.h>
namespace NActors {
class alignas(64) TCpuState {
// Atomic cachelign-aligned 64-bit state, see description below
TAtomic State = 0;
char Padding[64 - sizeof(TAtomic)];
// Bits 0-31: Currently executing pool
// - value less than MaxPools means cpu is executing corresponding pool (fast-worker is executing or waiting for slow-workers)
// - one of Cpu* values in case of idle cpu
// - used as futex by blocked fast-worker
static constexpr ui64 CurrentBits = 32;
static constexpr ui64 CurrentMask = ui64((1ull << CurrentBits) - 1);
// Bits 32-63: Assigned pool
// - value is set by balancer
// - NOT used as futex
// - Not balanced
static constexpr ui64 AssignedOffs = 32;
static constexpr ui64 AssignedMask = ~CurrentMask;
public:
TCpuState() {
Y_UNUSED(Padding);
}
void Load(TPoolId& assigned, TPoolId& current) const {
TAtomicBase state = AtomicLoad(&State);
assigned = (state & AssignedMask) >> AssignedOffs;
current = state & CurrentMask;
}
TPoolId CurrentPool() const {
return TPoolId(AtomicLoad(&State) & CurrentMask);
}
void SwitchPool(TPoolId pool) {
while (true) {
TAtomicBase state = AtomicLoad(&State);
if (AtomicCas(&State, (state & ~CurrentMask) | pool, state)) {
return;
}
}
}
TPoolId AssignedPool() const {
return TPoolId((AtomicLoad(&State) & AssignedMask) >> AssignedOffs);
}
// Assigns new pool to cpu and wakes it up if cpu is idle
void AssignPool(TPoolId pool) {
while (true) {
TAtomicBase state = AtomicLoad(&State);
TPoolId current(state & CurrentMask);
if (Y_UNLIKELY(current == CpuStopped)) {
return; // it would be better to shutdown instead of balancing
}
// Idle cpu must be woken up after balancing to handle pending tokens (if any) in assigned/schedulable pool(s)
if (current == CpuSpinning) {
if (AtomicCas(&State, (ui64(pool) << AssignedOffs) | pool, state)) {
return; // successfully woken up
}
} else if (current == CpuBlocked) {
if (AtomicCas(&State, (ui64(pool) << AssignedOffs) | pool, state)) {
FutexWake();
return; // successfully woken up
}
} else {
if (AtomicCas(&State, (ui64(pool) << AssignedOffs) | (state & ~AssignedMask), state)) {
return; // wakeup is not required
}
}
}
}
void Stop() {
while (true) {
TAtomicBase state = AtomicLoad(&State);
if (AtomicCas(&State, (state & ~CurrentMask) | CpuStopped, state)) {
FutexWake();
return; // successfully stopped
}
}
}
// Start waiting, returns false in case of actorsystem shutdown
bool StartSpinning() {
while (true) {
TAtomicBase state = AtomicLoad(&State);
TPoolId current(state & CurrentMask);
if (Y_UNLIKELY(current == CpuStopped)) {
return false;
}
Y_VERIFY_DEBUG(current < MaxPools, "unexpected already waiting state of cpu (%d)", (int)current);
if (AtomicCas(&State, (state & ~CurrentMask) | CpuSpinning, state)) { // successfully marked as spinning
return true;
}
}
}
bool StartBlocking() {
while (true) {
TAtomicBase state = AtomicLoad(&State);
TPoolId current(state & CurrentMask);
if (current == CpuSpinning) {
if (AtomicCas(&State, (state & ~CurrentMask) | CpuBlocked, state)) {
return false; // successful switch
}
} else {
return true; // wakeup
}
}
}
bool Block(ui64 timeoutNs, TPoolId& result) {
#ifdef _linux_
timespec timeout;
timeout.tv_sec = timeoutNs / 1'000'000'000;
timeout.tv_nsec = timeoutNs % 1'000'000'000;
SysFutex(Futex(), FUTEX_WAIT_PRIVATE, CpuBlocked, &timeout, nullptr, 0);
#else
NanoSleep(timeoutNs); // non-linux wake is not supported, cpu will go idle on wake after blocked state
#endif
TAtomicBase state = AtomicLoad(&State);
TPoolId current(state & CurrentMask);
if (current == CpuBlocked) {
return false; // timeout
} else {
result = current;
return true; // wakeup
}
}
enum EWakeResult {
Woken, // successfully woken up
NotIdle, // cpu is already not idle
Forbidden, // cpu is assigned to another pool
Stopped, // cpu is shutdown
};
EWakeResult WakeWithoutToken(TPoolId pool) {
while (true) {
TAtomicBase state = RelaxedLoad(&State);
TPoolId current(state & CurrentMask);
TPoolId assigned((state & AssignedMask) >> AssignedOffs);
if (assigned == CpuShared || assigned == pool) {
if (current == CpuSpinning) {
if (AtomicCas(&State, (state & ~CurrentMask) | pool, state)) {
return Woken;
}
} else if (current == CpuBlocked) {
if (AtomicCas(&State, (state & ~CurrentMask) | pool, state)) {
FutexWake();
return Woken;
}
} else if (current == CpuStopped) {
return Stopped;
} else {
return NotIdle;
}
} else {
return Forbidden;
}
}
}
EWakeResult WakeWithTokenAcquired(TPoolId token) {
while (true) {
TAtomicBase state = RelaxedLoad(&State);
TPoolId current(state & CurrentMask);
// NOTE: We ignore assigned value because we already have token, so
// NOTE: not assigned pool may be run here. This will be fixed
// NOTE: after we finish with current activation
if (current == CpuSpinning) {
if (AtomicCas(&State, (state & ~CurrentMask) | token, state)) {
return Woken;
}
} else if (current == CpuBlocked) {
if (AtomicCas(&State, (state & ~CurrentMask) | token, state)) {
FutexWake();
return Woken;
}
} else if (current == CpuStopped) {
return Stopped;
} else {
return NotIdle;
}
}
}
bool IsPoolReassigned(TPoolId current) const {
TAtomicBase state = AtomicLoad(&State);
TPoolId assigned((state & AssignedMask) >> AssignedOffs);
return assigned != current;
}
private:
void* Futex() {
return (void*)&State; // little endian assumed
}
void FutexWake() {
#ifdef _linux_
SysFutex(Futex(), FUTEX_WAKE_PRIVATE, 1, nullptr, nullptr, 0);
#endif
}
};
}
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