STDIN_FILENO的aio_read返回OS X中的EAGAIN

Question

当我在OS X中编译此代码时：

#include <unistd.h>
#include <iostream>
#include <memory>
#include <aio.h>
#include <sys/stat.h>
#include <fcntl.h>
using namespace std;

int main(int, char*[])
{
    const int iBufSize = 1<<20;
    unique_ptr<char[]> pBuffer(new char[iBufSize]);
    int iRet;

    int iOpts = fcntl(STDIN_FILENO, F_GETFL);
    cout << "GETFL Before: " << iOpts << endl;
    fcntl(STDIN_FILENO, F_SETFL, iOpts & ~O_NONBLOCK);
    iOpts = fcntl(STDIN_FILENO, F_GETFL);
    cout << "GETFL After: " << iOpts << endl;

    aiocb cb = {0};
    cb.aio_fildes = STDIN_FILENO;
    cb.aio_buf = pBuffer.get();
    cb.aio_nbytes = iBufSize;
    iRet = aio_read(&cb);
    cout << "aio_read retuned " << iRet << endl;
    cout << "errno = " << strerror(errno) << "(" << errno << ")" << endl;
    return 0;
}

用g ++编译它，然后执行它：

echo "Hello" | ./aio_read\ demo

它返回：

GETFL Before: 0
GETFL After: 0
aio_read retuned -1
errno = Resource temporarily unavailable(35)

为什么呢？如果我在没有前面的echo "Hello" |的情况下运行它，它会按预期工作。此外，fcntl调用不是引起问题所必需的，但它们确实显示STDIN没有设置O_NONBLOCK。