mengrao / wfmpmc Goto Github PK

"Even worse, if a writer holding an index crashes before committing, then the corresponding reader will never succeed in reading one element even if other writer has completed a write operation. This is the reason why WFMPMC is not strict wait-free."
Well, with this behaviour it is not even lock-free as lock-freedom requires system-wide progress (some thread must make progress) even if one thread fails or blocks.

With loops like this: "while((data = getWritable(idx)) == nullptr);", it is actually blocking. Essentially, each individual slot is protected by its own lock (which allows for alternating enqueues and dequeues). Any thread that continues to enqueue/dequeue objects will eventually attempt to access all slots, including any slot that is blocked.

这个函数虽然是个while,但是这么看都只运行了一次吧！？

看不懂, 理解不了...

如果pop有阻塞，那么push就会失败，这个感觉没啥用，queue都没buf

WFMPMC.h 57行那里，init_state我遇到了一种情况：init_state 为一个2打头的随机值，然后就卡在那行

在shm_comm.h中， 函数shmmap()里面，在 ret->shmInit();语句之前，少了一个 调用T构造函数。
'''
T* ret = (T*)mmap(0, sizeof(T), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
close(fd);

if(ret == MAP_FAILED) 
{
    std::cerr << "mmap failed: " << strerror(errno) << std::endl;
    return nullptr;
}

new(ret) T(); //这一句

ret->shmInit();

'''

会导致一个问题是，mmap的文件如果是存在的，WFMPMC对象在共享内存上没有调用构造函数，导致readidx,wirteidx 没有正确赋值

如果队列为空，while (try read); 是一个会把cpu core吃满的操作，在实际工程中适用范围很小。

此处需要一个std::condition_variable来等待，引入condition又会有新的问题，不是使用者直接引入就能解决的，应该还是需要wait-free队列处理好这个事情。