mirror of
https://github.com/dolphin-emu/dolphin.git
synced 2025-07-23 22:29:39 -06:00
Core: Threadsafety Synchronization Fixes (Frame Advance / FifoPlayer)
Fix Frame Advance and FifoPlayer pause/unpause/stop. CPU::EnableStepping is not atomic but is called from multiple threads which races and leaves the system in a random state; also instruction stepping was unstable, m_StepEvent had an almost random value because of the dual purpose it served which could cause races where CPU::Run would SingleStep when it was supposed to be sleeping. FifoPlayer never FinishStateMove()d which was causing it to deadlock. Rather than partially reimplementing CPU::Run, just use CPUCoreBase and then call CPU::Run(). More DRY and less likely to have weird bugs specific to the player (i.e the previous freezing on pause/stop). Refactor PowerPC::state into CPU since it manages the state of the CPU Thread which is controlled by CPU, not PowerPC. This simplifies the architecture somewhat and eliminates races that can be caused by calling PowerPC state functions directly instead of using CPU's (because they bypassed the EnableStepping lock).
This commit is contained in:
EmptyChaos
@ -2,11 +2,13 @@
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// Licensed under GPLv2+
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// Refer to the license.txt file included.
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#include <condition_variable>
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#include <mutex>
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#include "AudioCommon/AudioCommon.h"
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#include "Common/CommonTypes.h"
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#include "Common/Event.h"
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#include "Common/Logging/Log.h"
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#include "Core/Core.h"
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#include "Core/Host.h"
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#include "Core/HW/CPU.h"
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@ -14,82 +16,177 @@
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#include "Core/PowerPC/PowerPC.h"
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#include "VideoCommon/Fifo.h"
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namespace
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{
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static Common::Event m_StepEvent;
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static Common::Event *m_SyncEvent = nullptr;
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static std::mutex m_csCpuOccupied;
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}
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namespace CPU
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{
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// CPU Thread execution state.
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// Requires s_state_change_lock to modify the value.
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// Read access is unsynchronized.
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static State s_state = CPU_POWERDOWN;
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// Synchronizes EnableStepping and PauseAndLock so only one instance can be
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// active at a time. Simplifies code by eliminating several edge cases where
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// the EnableStepping(true)/PauseAndLock(true) case must release the state lock
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// and wait for the CPU Thread which would otherwise require additional flags.
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// NOTE: When using the stepping lock, it must always be acquired first. If
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// the lock is acquired after the state lock then that is guaranteed to
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// deadlock because of the order inversion. (A -> X,Y; B -> Y,X; A waits for
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// B, B waits for A)
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static std::mutex s_stepping_lock;
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// Primary lock. Protects changing s_state, requesting instruction stepping and
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// pause-and-locking.
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static std::mutex s_state_change_lock;
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// When s_state_cpu_thread_active changes to false
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static std::condition_variable s_state_cpu_idle_cvar;
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// When s_state changes / s_state_paused_and_locked becomes false (for CPU Thread only)
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static std::condition_variable s_state_cpu_cvar;
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static bool s_state_cpu_thread_active = false;
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static bool s_state_paused_and_locked = false;
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static bool s_state_system_request_stepping = false;
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static bool s_state_cpu_step_instruction = false;
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static Common::Event* s_state_cpu_step_instruction_sync = nullptr;
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void Init(int cpu_core)
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{
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PowerPC::Init(cpu_core);
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m_SyncEvent = nullptr;
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s_state = CPU_STEPPING;
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}
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void Shutdown()
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{
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Stop();
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PowerPC::Shutdown();
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m_SyncEvent = nullptr;
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}
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// Requires holding s_state_change_lock
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static void FlushStepSyncEventLocked()
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{
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if (s_state_cpu_step_instruction_sync)
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{
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s_state_cpu_step_instruction_sync->Set();
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s_state_cpu_step_instruction_sync = nullptr;
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}
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s_state_cpu_step_instruction = false;
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}
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void Run()
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{
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std::lock_guard<std::mutex> lk(m_csCpuOccupied);
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Host_UpdateDisasmDialog();
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while (true)
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std::unique_lock<std::mutex> state_lock(s_state_change_lock);
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while (s_state != CPU_POWERDOWN)
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{
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switch (PowerPC::GetState())
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s_state_cpu_cvar.wait(state_lock, [] { return !s_state_paused_and_locked; });
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switch (s_state)
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{
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case PowerPC::CPU_RUNNING:
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//1: enter a fast runloop
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case CPU_RUNNING:
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s_state_cpu_thread_active = true;
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state_lock.unlock();
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// Adjust PC for JIT when debugging
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// SingleStep so that the "continue", "step over" and "step out" debugger functions
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// work when the PC is at a breakpoint at the beginning of the block
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// If watchpoints are enabled, any instruction could be a breakpoint.
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if (PowerPC::GetMode() != PowerPC::MODE_INTERPRETER)
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{
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#ifndef ENABLE_MEM_CHECK
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if (PowerPC::breakpoints.IsAddressBreakPoint(PC))
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#endif
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{
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PowerPC::CoreMode old_mode = PowerPC::GetMode();
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PowerPC::SetMode(PowerPC::MODE_INTERPRETER);
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PowerPC::SingleStep();
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PowerPC::SetMode(old_mode);
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}
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}
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// Enter a fast runloop
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PowerPC::RunLoop();
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state_lock.lock();
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s_state_cpu_thread_active = false;
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s_state_cpu_idle_cvar.notify_all();
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break;
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case PowerPC::CPU_STEPPING:
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m_csCpuOccupied.unlock();
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//1: wait for step command..
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m_StepEvent.Wait();
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m_csCpuOccupied.lock();
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if (PowerPC::GetState() == PowerPC::CPU_POWERDOWN)
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return;
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if (PowerPC::GetState() != PowerPC::CPU_STEPPING)
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case CPU_STEPPING:
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// Wait for step command.
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s_state_cpu_cvar.wait(state_lock, []
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{
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return s_state_cpu_step_instruction ||
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s_state != CPU_STEPPING;
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});
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if (s_state != CPU_STEPPING)
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{
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// Signal event if the mode changes.
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FlushStepSyncEventLocked();
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continue;
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}
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if (s_state_paused_and_locked)
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continue;
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//3: do a step
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// Do step
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s_state_cpu_thread_active = true;
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state_lock.unlock();
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PowerPC::SingleStep();
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//4: update disasm dialog
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if (m_SyncEvent)
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{
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m_SyncEvent->Set();
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m_SyncEvent = nullptr;
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}
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state_lock.lock();
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s_state_cpu_thread_active = false;
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s_state_cpu_idle_cvar.notify_all();
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// Update disasm dialog
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FlushStepSyncEventLocked();
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Host_UpdateDisasmDialog();
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break;
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case PowerPC::CPU_POWERDOWN:
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//1: Exit loop!!
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return;
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case CPU_POWERDOWN:
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break;
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}
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}
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state_lock.unlock();
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Host_UpdateDisasmDialog();
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}
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// Requires holding s_state_change_lock
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static void RunAdjacentSystems(bool running)
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{
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// NOTE: We're assuming these will not try to call Break or EnableStepping.
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Fifo::EmulatorState(running);
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AudioCommon::ClearAudioBuffer(!running);
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}
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void Stop()
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{
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PowerPC::Stop();
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m_StepEvent.Set();
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// Change state and wait for it to be acknowledged.
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// We don't need the stepping lock because CPU_POWERDOWN is a priority state which
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// will stick permanently.
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std::unique_lock<std::mutex> state_lock(s_state_change_lock);
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s_state = CPU_POWERDOWN;
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s_state_cpu_cvar.notify_one();
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// FIXME: MsgHandler can cause this to deadlock the GUI Thread. Remove the timeout.
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bool success = s_state_cpu_idle_cvar.wait_for(state_lock, std::chrono::seconds(5), []
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{
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return !s_state_cpu_thread_active;
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});
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if (!success)
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ERROR_LOG(POWERPC, "CPU Thread failed to acknowledge CPU_POWERDOWN. It may be deadlocked.");
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RunAdjacentSystems(false);
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FlushStepSyncEventLocked();
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}
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bool IsStepping()
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{
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return PowerPC::GetState() == PowerPC::CPU_STEPPING;
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return s_state == CPU_STEPPING;
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}
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State GetState()
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{
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return s_state;
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}
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const volatile State* GetStatePtr()
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{
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return &s_state;
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}
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void Reset()
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@ -98,87 +195,142 @@ void Reset()
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void StepOpcode(Common::Event* event)
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{
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m_StepEvent.Set();
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if (PowerPC::GetState() == PowerPC::CPU_STEPPING)
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std::lock_guard<std::mutex> state_lock(s_state_change_lock);
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// If we're not stepping then this is pointless
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if (!IsStepping())
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{
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m_SyncEvent = event;
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if (event)
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event->Set();
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return;
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}
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// Potential race where the previous step has not been serviced yet.
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if (s_state_cpu_step_instruction_sync && s_state_cpu_step_instruction_sync != event)
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s_state_cpu_step_instruction_sync->Set();
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s_state_cpu_step_instruction = true;
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s_state_cpu_step_instruction_sync = event;
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s_state_cpu_cvar.notify_one();
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}
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void EnableStepping(const bool stepping)
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// Requires s_state_change_lock
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static bool SetStateLocked(State s)
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{
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if (s_state == CPU_POWERDOWN)
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return false;
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s_state = s;
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return true;
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}
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void EnableStepping(bool stepping)
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{
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std::lock_guard<std::mutex> stepping_lock(s_stepping_lock);
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std::unique_lock<std::mutex> state_lock(s_state_change_lock);
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if (stepping)
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{
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PowerPC::Pause();
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m_StepEvent.Reset();
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Fifo::EmulatorState(false);
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AudioCommon::ClearAudioBuffer(true);
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}
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else
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{
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// SingleStep so that the "continue", "step over" and "step out" debugger functions
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// work when the PC is at a breakpoint at the beginning of the block
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// If watchpoints are enabled, any instruction could be a breakpoint.
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bool could_be_bp;
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#ifdef ENABLE_MEM_CHECK
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could_be_bp = true;
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#else
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could_be_bp = PowerPC::breakpoints.IsAddressBreakPoint(PC);
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#endif
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if (could_be_bp && PowerPC::GetMode() != PowerPC::MODE_INTERPRETER)
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SetStateLocked(CPU_STEPPING);
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// Wait for the CPU Thread to leave the run loop
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// FIXME: MsgHandler can cause this to deadlock the GUI Thread. Remove the timeout.
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bool success = s_state_cpu_idle_cvar.wait_for(state_lock, std::chrono::seconds(5), []
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{
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PowerPC::CoreMode oldMode = PowerPC::GetMode();
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PowerPC::SetMode(PowerPC::MODE_INTERPRETER);
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PowerPC::SingleStep();
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PowerPC::SetMode(oldMode);
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}
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PowerPC::Start();
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m_StepEvent.Set();
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Fifo::EmulatorState(true);
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AudioCommon::ClearAudioBuffer(false);
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return !s_state_cpu_thread_active;
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});
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if (!success)
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ERROR_LOG(POWERPC, "Abandoned waiting for CPU Thread! The Core may be deadlocked.");
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RunAdjacentSystems(false);
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}
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else if (SetStateLocked(CPU_RUNNING))
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{
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s_state_cpu_cvar.notify_one();
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RunAdjacentSystems(true);
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}
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}
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void Break()
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{
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EnableStepping(true);
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std::lock_guard<std::mutex> state_lock(s_state_change_lock);
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// If another thread is trying to PauseAndLock then we need to remember this
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// for later to ignore the unpause_on_unlock.
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if (s_state_paused_and_locked)
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{
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s_state_system_request_stepping = true;
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return;
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}
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// We'll deadlock if we synchronize, the CPU may block waiting for our caller to
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// finish resulting in the CPU loop never terminating.
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SetStateLocked(CPU_STEPPING);
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RunAdjacentSystems(false);
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}
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bool PauseAndLock(bool do_lock, bool unpause_on_unlock)
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bool PauseAndLock(bool do_lock, bool unpause_on_unlock, bool control_adjacent)
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{
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static bool s_have_fake_cpu_thread;
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bool wasUnpaused = !IsStepping();
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// NOTE: This is protected by s_stepping_lock.
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static bool s_have_fake_cpu_thread = false;
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bool was_unpaused = false;
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if (do_lock)
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{
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// we can't use EnableStepping, that would causes deadlocks with both audio and video
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PowerPC::Pause();
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s_stepping_lock.lock();
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std::unique_lock<std::mutex> state_lock(s_state_change_lock);
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s_state_paused_and_locked = true;
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was_unpaused = s_state == CPU_RUNNING;
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SetStateLocked(CPU_STEPPING);
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// FIXME: MsgHandler can cause this to deadlock the GUI Thread. Remove the timeout.
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bool success = s_state_cpu_idle_cvar.wait_for(state_lock, std::chrono::seconds(10), []
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{
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return !s_state_cpu_thread_active;
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});
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if (!success)
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NOTICE_LOG(POWERPC, "Abandoned CPU Thread synchronization in CPU::PauseAndLock! We'll probably crash now.");
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if (control_adjacent)
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RunAdjacentSystems(false);
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state_lock.unlock();
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// NOTE: It would make more sense for Core::DeclareAsCPUThread() to keep a
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// depth counter instead of being a boolean.
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if (!Core::IsCPUThread())
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{
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m_csCpuOccupied.lock();
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s_have_fake_cpu_thread = true;
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Core::DeclareAsCPUThread();
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}
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else
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{
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s_have_fake_cpu_thread = false;
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}
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}
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else
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{
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if (unpause_on_unlock)
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{
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PowerPC::Start();
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m_StepEvent.Set();
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}
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// Only need the stepping lock for this
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if (s_have_fake_cpu_thread)
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{
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Core::UndeclareAsCPUThread();
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m_csCpuOccupied.unlock();
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s_have_fake_cpu_thread = false;
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Core::UndeclareAsCPUThread();
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}
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{
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std::lock_guard<std::mutex> state_lock(s_state_change_lock);
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if (s_state_system_request_stepping)
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{
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s_state_system_request_stepping = false;
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}
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else if (unpause_on_unlock && SetStateLocked(CPU_RUNNING))
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{
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was_unpaused = true;
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}
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s_state_paused_and_locked = false;
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s_state_cpu_cvar.notify_one();
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if (control_adjacent)
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RunAdjacentSystems(s_state == CPU_RUNNING);
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}
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s_stepping_lock.unlock();
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}
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return wasUnpaused;
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return was_unpaused;
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}
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}
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Block a user