Friday, January 15, 2021

Digest for comp.lang.c++@googlegroups.com - 13 updates in 1 topic

"Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: Jan 14 04:15PM -0800

On 1/13/2021 10:51 PM, Chris M. Thomasson wrote:
> thing, vs one that uses a normal kernel object for the slow path.
 
> You can use a benaphore or any other mutex you want vs futex as a test
> vector.
 
 
Can you run this Bonita? Fwiw, it would be my first time using a Windows
Futex! lol:
______________________________________
#include <iostream>
#include <thread>
#include <functional>
 
#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
 
 
#define CT_L2_ALIGNMENT 128
#define CT_THREADS 32
#define CT_ITERS 6666666
 
 
struct ct_futex_mutex
{
ULONG alignas(CT_L2_ALIGNMENT) m_state;
 
ct_futex_mutex() : m_state(0)
{
 
}
 
void lock()
{
if (InterlockedExchange(&m_state, 1))
{
while (InterlockedExchange(&m_state, 2))
{
ULONG cmp = 2;
WaitOnAddress(&m_state, &cmp, sizeof(ULONG), INFINITE);
}
}
}
 
void unlock()
{
if (InterlockedExchange(&m_state, 0) == 2)
{
WakeByAddressSingle(&m_state);
}
}
};
 
 
struct ct_shared
{
ct_futex_mutex m_mtx;
unsigned long m_count;
 
ct_shared() : m_count(0) {}
 
~ct_shared()
{
if (m_count != 0)
{
std::cout << "counter is totally fubar!\n";
}
}
};
 
 
void ct_thread(ct_shared& shared)
{
for (unsigned long i = 0; i < CT_ITERS; ++i)
{
shared.m_mtx.lock();
++shared.m_count;
shared.m_mtx.unlock();
 
shared.m_mtx.lock();
--shared.m_count;
shared.m_mtx.unlock();
}
}
 
 
int main()
{
std::thread threads[CT_THREADS];
 
std::cout << "Starting up...\n";
 
{
ct_shared shared;
 
for (unsigned long i = 0; i < CT_THREADS; ++i)
{
threads[i] = std::thread(ct_thread, std::ref(shared));
}
 
std::cout << "Running...\n";
 
for (unsigned long i = 0; i < CT_THREADS; ++i)
{
threads[i].join();
}
}
 
std::cout << "Completed!\n";
 
return 0;
}
______________________________________
 
 
Afaict, it should work. I have not tested this in Relacy yet.
Bonita Montero <Bonita.Montero@gmail.com>: Jan 15 08:56AM +0100

> Afaict, it should work. I have not tested this in Relacy yet.
 
It works. And it's not necessary to test such simple code
with Relacy or whatever.
 
I yesterday wrote a portable semaphore-class:
 
// fsemaphore.h
 
#pragma once
#if defined(_MSC_VER)
#include <Windows.h>
#elif defined(__gnu_linux__)
#include <unistd.h>
#include <linux/futex.h>
#include <stdint.h>
#include <sys/time.h>
#include <sys/syscall.h>
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