lokinet/llarp/util/thread/threading.hpp

#ifndef LLARP_THREADING_HPP
#define LLARP_THREADING_HPP

#include <absl/synchronization/barrier.h>
#include <absl/synchronization/mutex.h>
#include <absl/types/optional.h>
#include <absl/time/time.h>

#include <iostream>
#include <thread>

#if defined(WIN32) && !defined(__GNUC__)
#include <process.h>
using pid_t = int;
#else
#include <sys/types.h>
#include <unistd.h>
#endif

#ifdef TRACY_ENABLE
#include "Tracy.hpp"
#define DECLARE_LOCK(type, var, ...) TracyLockable(type, var)
#define ACQUIRE_LOCK(lock, mtx) lock(mtx)
#else
#define DECLARE_LOCK(type, var, ...) type var __VA_ARGS__
#define ACQUIRE_LOCK(lock, mtx) lock(&mtx)
#endif

namespace llarp
{
  namespace util
  {
    /// a mutex that does nothing
    ///
    /// this exists to convert mutexes that were initially in use (but may no
    /// longer be necessary) into no-op placeholders (except in debug mode
    /// where they complain loudly when they are actually accessed across
    /// different threads; see below).
    ///
    /// the idea is to "turn off" the mutexes and see where they are actually
    /// needed.
    struct LOCKABLE NullMutex
    {
#ifdef LOKINET_DEBUG
      /// in debug mode, we implement lock() to enforce that any lock is only
      /// used from a single thread. the point of this is to identify locks that
      /// are actually needed by dying a painful death when used across threads
      mutable absl::optional< std::thread::id > m_id;
      void
      lock() const
      {
        if(!m_id)
        {
          m_id.emplace(std::this_thread::get_id());
        }
        else if(m_id.value() != std::this_thread::get_id())
        {
          std::cerr << "NullMutex " << this
                    << " was used across threads: locked by "
                    << std::this_thread::get_id()
                    << " and was previously locked by " << m_id.value() << "\n";
          // if you're encountering this abort() call, you may have discovered a
          // case where a NullMutex should be reverted to a "real mutex"
          std::abort();
        }
      }
#else
      void
      lock() const
      {
      }
#endif
    };

    /// a lock that does nothing
    struct SCOPED_LOCKABLE NullLock
    {
      NullLock(ABSL_ATTRIBUTE_UNUSED const NullMutex* mtx)
          EXCLUSIVE_LOCK_FUNCTION(mtx)
      {
        mtx->lock();
      }

      ~NullLock() UNLOCK_FUNCTION()
      {
        (void)this;  // trick clang-tidy
      }
    };

    using Mutex = absl::Mutex;
    using Lock  = absl::MutexLock;

    using ReleasableLock = absl::ReleasableMutexLock;
    using Condition      = absl::CondVar;

    class Semaphore
    {
     private:
      Mutex m_mutex;  // protects m_count
      size_t m_count GUARDED_BY(m_mutex);

      bool
      ready() const SHARED_LOCKS_REQUIRED(m_mutex)
      {
        return m_count > 0;
      }

     public:
      Semaphore(size_t count) : m_count(count)
      {
      }

      void
      notify() LOCKS_EXCLUDED(m_mutex)
      {
        Lock lock(&m_mutex);
        m_count++;
      }

      void
      wait() LOCKS_EXCLUDED(m_mutex)
      {
        Lock lock(&m_mutex);
        m_mutex.Await(absl::Condition(this, &Semaphore::ready));

        m_count--;
      }

      bool
      waitFor(absl::Duration timeout) LOCKS_EXCLUDED(m_mutex)
      {
        Lock lock(&m_mutex);

        if(!m_mutex.AwaitWithTimeout(absl::Condition(this, &Semaphore::ready),
                                     timeout))
        {
          return false;
        }

        m_count--;
        return true;
      }
    };

    using Barrier = absl::Barrier;

    void
    SetThreadName(const std::string& name);

    inline pid_t
    GetPid()
    {
#ifdef WIN32
      return _getpid();
#else
      return ::getpid();
#endif
    }

    // type for detecting contention on a resource
    struct ContentionKiller
    {
      void
      TryAccess(std::function< void(void) > visit) const;

     private:
      mutable NullMutex __access;
    };
  }  // namespace util
}  // namespace llarp

#endif