Created
August 13, 2021 19:01
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comparing mfence and mutes
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// g++ -O3 -lpthread -march=athlon64-sse3 -std=c++17 barier_and_mutexes.cpp -o barrier_and_mutexes | |
#include <stdio.h> | |
#include <cstdint> | |
#include <cstdlib> | |
#include <atomic> | |
#include <vector> | |
#include <thread> | |
#include <mutex> | |
#include <cassert> | |
int const nMaxThreads = std::thread::hardware_concurrency(); | |
std::vector<std::thread> threads; | |
std::atomic<void*> head; | |
std::atomic<void*> data; | |
std::atomic<int*> p=nullptr; | |
typedef struct {int v,c; }myData; | |
// myData data2; | |
void modifyData(std::atomic<void*> d){} | |
void _proceedTest(std::atomic<void*> data2){ | |
static std::mutex mtx; | |
std::unique_lock<std::mutex> lk(mtx); | |
modifyData(&data2); | |
lk.unlock(); | |
} | |
int main(){ | |
int* regularVar1=0; | |
regularVar1++; | |
//head.store(0, std::memory_order_relaxed); | |
head.store(regularVar1,std::memory_order_seq_cst); | |
//std::atomic_thread_fence(std::memory_order_seq_cst); | |
data = head.load(std::memory_order_relaxed); | |
//std::atomic_thread_fence(std::memory_order_seq_cst); | |
p = regularVar1; | |
//first thread | |
{ | |
int* nonatomic_p=(int*) malloc(16*1024*sizeof(int)); | |
for(int i=0;i<16*1024;++i) | |
nonatomic_p[i]=42; | |
p=nonatomic_p; | |
} | |
//second thread reads | |
{ | |
while (p==nullptr) | |
{} | |
assert(p[1234]==42);//1234-random idx in array | |
} | |
for (int iThread = 0; iThread < nMaxThreads; ++iThread) | |
{ | |
threads.push_back(std::thread(_proceedTest, &head)); | |
} | |
for (auto& th : threads) th.join(); | |
} |
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