What is the C++ equivalent for AutoResetEvent under Linux?

Conditional variables are NOT the equivalent of AutoResetEvent. They are the equivalent of Monitors. The difference is critical and may cause deadlocks if not used properly:

Imagine two threads A and B in a C# program. A calls WaitOne() and B calls Set(). If B executes Set() before A reaches the call to WaitOne(), there is no problem because the signal sent to the AutoResetEvent() by Set() is persistent and it will remain set until a WaitOne() is executed.

Now in C, imagine two threads C and D. C calls wait(), D calls notify(). If C is waiting already when D calls notify() everything is ok. If C did not manage to reach wait() before D calls notify(), you have a deadlock because the signal is lost if nobody is waiting on it and the status of the conditional variable is still "unset".

Be very careful about this.

I'm pretty sure you're looking for condition variables. The accepted answer to this other SO question: Condition variables in C# -- seems to confirm it.

See e.g. this tutorial for details on condition variables in POSIX threads.

An AutoResetEvent is most akin to a binary semaphore. People saying "conditional variables" aren't wrong per se, but condition variables are used in similar situations, rather than being similar objects. You can implement an (unnamed) AutoResetEvent on top of condition variables:

#include <pthread.h>
#include <stdio.h>

class AutoResetEvent
{
  public:
  explicit AutoResetEvent(bool initial = false);

  ~AutoResetEvent();
  void Set();
  void Reset();

  bool WaitOne();

  private:
  AutoResetEvent(const AutoResetEvent&);
  AutoResetEvent& operator=(const AutoResetEvent&); // non-copyable
  bool flag_;
  pthread_mutex_t protect_;
  pthread_cond_t signal_;
};

AutoResetEvent::AutoResetEvent(bool initial)
: flag_(initial)
{
  pthread_mutex_init(&protect_, NULL);
  pthread_cond_init(&signal_, NULL);
}

void AutoResetEvent::Set()
{
  pthread_mutex_lock(&protect_);
  flag_ = true;
  pthread_mutex_unlock(&protect_);
  pthread_cond_signal(&signal_);
}

void AutoResetEvent::Reset()
{
  pthread_mutex_lock(&protect_);
  flag_ = false;
  pthread_mutex_unlock(&protect_);
}

bool AutoResetEvent::WaitOne()
{
  pthread_mutex_lock(&protect_);
  while( !flag_ ) // prevent spurious wakeups from doing harm
    pthread_cond_wait(&signal_, &protect_);
  flag_ = false; // waiting resets the flag
  pthread_mutex_unlock(&protect_);
  return true;
}

AutoResetEvent::~AutoResetEvent()
{
  pthread_mutex_destroy(&protect_);
  pthread_cond_destroy(&signal_);
}


AutoResetEvent event;

void *otherthread(void *)
{
  event.WaitOne();
  printf("Hello from other thread!\n");
  return NULL;
}


int main()
{
  pthread_t h;
  pthread_create(&h, NULL, &otherthread, NULL);
  printf("Hello from the first thread\n");
  event.Set();

  pthread_join(h, NULL);
  return 0;
}

If however, you need named auto reset events, you'll likely want to look at semaphores, and may have a slightly more difficult time translating your code. Either way I would look careful at the documentation for pthreads on your platform, condition variables and auto reset events are not the same and do not behave the same.