FEX-Emu--FEX/Source/Tools/LinuxEmulation/LinuxSyscalls/ThreadManager.cpp

// SPDX-License-Identifier: MIT

#include "LinuxSyscalls/Syscalls.h"
#include "LinuxSyscalls/SignalDelegator.h"

#include <FEXHeaderUtils/Syscalls.h>

namespace FEX::HLE {
  FEXCore::Core::InternalThreadState *ThreadManager::CreateThread(uint64_t InitialRIP, uint64_t StackPointer, FEXCore::Core::CPUState *NewThreadState, uint64_t ParentTID) {
    auto Thread = CTX->CreateThread(InitialRIP, StackPointer, NewThreadState, ParentTID);

    ++IdleWaitRefCount;
    return Thread;
  }

  void ThreadManager::DestroyThread(FEXCore::Core::InternalThreadState *Thread) {
    {
      std::lock_guard lk(ThreadCreationMutex);
      auto It = std::find(Threads.begin(), Threads.end(), Thread);
      LOGMAN_THROW_A_FMT(It != Threads.end(), "Thread wasn't in Threads");
      Threads.erase(It);
    }

    HandleThreadDeletion(Thread);
  }

  void ThreadManager::StopThread(FEXCore::Core::InternalThreadState *Thread) {
    if (Thread->RunningEvents.Running.exchange(false)) {
      SignalDelegation->SignalThread(Thread, FEXCore::Core::SignalEvent::Stop);
    }
  }

  void ThreadManager::RunThread(FEXCore::Core::InternalThreadState *Thread) {
    // Tell the thread to start executing
    Thread->StartRunning.NotifyAll();
  }

  void ThreadManager::HandleThreadDeletion(FEXCore::Core::InternalThreadState *Thread) {
    if (Thread->ExecutionThread) {
      if (Thread->ExecutionThread->joinable()) {
        Thread->ExecutionThread->join(nullptr);
      }

      if (Thread->ExecutionThread->IsSelf()) {
        Thread->ExecutionThread->detach();
      }
    }

    CTX->DestroyThread(Thread);
    --IdleWaitRefCount;
    IdleWaitCV.notify_all();
  }

  void ThreadManager::NotifyPause() {
    // Tell all the threads that they should pause
    std::lock_guard lk(ThreadCreationMutex);
    for (auto &Thread : Threads) {
      SignalDelegation->SignalThread(Thread, FEXCore::Core::SignalEvent::Pause);
    }
  }

  void ThreadManager::Pause() {
    NotifyPause();
    WaitForIdle();
  }

  void ThreadManager::Run() {
    // Spin up all the threads
    std::lock_guard lk(ThreadCreationMutex);
    for (auto &Thread : Threads) {
      Thread->SignalReason.store(FEXCore::Core::SignalEvent::Return);
    }

    for (auto &Thread : Threads) {
      Thread->StartRunning.NotifyAll();
    }
  }

  void ThreadManager::WaitForIdleWithTimeout() {
    std::unique_lock<std::mutex> lk(IdleWaitMutex);
    bool WaitResult = IdleWaitCV.wait_for(lk, std::chrono::milliseconds(1500),
      [this] {
        return IdleWaitRefCount.load() == 0;
    });

    if (!WaitResult) {
      // The wait failed, this will occur if we stepped in to a syscall
      // That's okay, we just need to pause the threads manually
      NotifyPause();
    }

    // We have sent every thread a pause signal
    // Now wait again because they /will/ be going to sleep
    WaitForIdle();
  }

  void ThreadManager::WaitForThreadsToRun() {
    size_t NumThreads{};
    {
      std::lock_guard lk(ThreadCreationMutex);
      NumThreads = Threads.size();
    }

    // Spin while waiting for the threads to start up
    std::unique_lock<std::mutex> lk(IdleWaitMutex);
    IdleWaitCV.wait(lk, [this, NumThreads] {
      return IdleWaitRefCount.load() >= NumThreads;
    });

    Running = true;
  }

  void ThreadManager::Step() {
    LogMan::Msg::AFmt("ThreadManager::Step currently not implemented");
    {
      std::lock_guard lk(ThreadCreationMutex);
      // Walk the threads and tell them to clear their caches
      // Useful when our block size is set to a large number and we need to step a single instruction
      for (auto &Thread : Threads) {
        CTX->ClearCodeCache(Thread);
      }
    }

    // TODO: Set to single step mode.
    Run();
    WaitForThreadsToRun();
    WaitForIdle();
    // TODO: Set back to full running mode.
  }

  void ThreadManager::Stop(bool IgnoreCurrentThread) {
    pid_t tid = FHU::Syscalls::gettid();
    FEXCore::Core::InternalThreadState* CurrentThread{};

    // Tell all the threads that they should stop
    {
      std::lock_guard lk(ThreadCreationMutex);
      for (auto &Thread : Threads) {
        if (IgnoreCurrentThread &&
            Thread->ThreadManager.TID == tid) {
          // If we are callign stop from the current thread then we can ignore sending signals to this thread
          // This means that this thread is already gone
        }
        else if (Thread->ThreadManager.TID == tid) {
          // We need to save the current thread for last to ensure all threads receive their stop signals
          CurrentThread = Thread;
          continue;
        }

        if (Thread->RunningEvents.Running.load()) {
          StopThread(Thread);
        }

        // If the thread is waiting to start but immediately killed then there can be a hang
        // This occurs in the case of gdb attach with immediate kill
        if (Thread->RunningEvents.WaitingToStart.load()) {
          Thread->RunningEvents.EarlyExit = true;
          Thread->StartRunning.NotifyAll();
        }
      }
    }

    // Stop the current thread now if we aren't ignoring it
    if (CurrentThread) {
      StopThread(CurrentThread);
    }
  }

  void ThreadManager::SleepThread(FEXCore::Context::Context *CTX, FEXCore::Core::CpuStateFrame *Frame) {
    auto Thread = Frame->Thread;

    --IdleWaitRefCount;
    IdleWaitCV.notify_all();

    Thread->RunningEvents.ThreadSleeping = true;

    // Go to sleep
    Thread->StartRunning.Wait();

    Thread->RunningEvents.Running = true;
    ++IdleWaitRefCount;
    Thread->RunningEvents.ThreadSleeping = false;

    IdleWaitCV.notify_all();
  }

  void ThreadManager::UnlockAfterFork(FEXCore::Core::InternalThreadState *LiveThread, bool Child) {
    if (!Child) return;

    // This function is called after fork
    // We need to cleanup some of the thread data that is dead
    for (auto &DeadThread : Threads) {
      if (DeadThread == LiveThread) {
        continue;
      }

      // Setting running to false ensures that when they are shutdown we won't send signals to kill them
      DeadThread->RunningEvents.Running = false;

      // Despite what google searches may susgest, glibc actually has special code to handle forks
      // with multiple active threads.
      // It cleans up the stacks of dead threads and marks them as terminated.
      // It also cleans up a bunch of internal mutexes.

      // FIXME: TLS is probally still alive. Investigate

      // Deconstructing the Interneal thread state should clean up most of the state.
      // But if anything on the now deleted stack is holding a refrence to the heap, it will be leaked
      CTX->DestroyThread(DeadThread);

      // FIXME: Make sure sure nothing gets leaked via the heap. Ideas:
      //         * Make sure nothing is allocated on the heap without ref in InternalThreadState
      //         * Surround any code that heap allocates with a per-thread mutex.
      //           Before forking, the the forking thread can lock all thread mutexes.
    }

    // Remove all threads but the live thread from Threads
    Threads.clear();
    Threads.push_back(LiveThread);

    // Clean up dead stacks
    FEXCore::Threads::Thread::CleanupAfterFork();

    // We now only have one thread.
    IdleWaitRefCount = 1;
  }

  void ThreadManager::WaitForIdle() {
    std::unique_lock<std::mutex> lk(IdleWaitMutex);
    IdleWaitCV.wait(lk, [this] {
      return IdleWaitRefCount.load() == 0;
    });

    Running = false;
  }

  ThreadManager::~ThreadManager() {
    std::lock_guard lk(ThreadCreationMutex);

    for (auto &Thread : Threads) {
      HandleThreadDeletion(Thread);
    }
    Threads.clear();
  }
}