How to get user data for aio signal handler in Mac OS X

Question

I'm trying to use the aio_ * functions for asynchronous IO I / O on Mac OS X, but I'm having problems getting some form of user data into a signal handler.

This is the code that sets up the operation:

class aio_context {
public:
    aio_context(int fildes, boost::uint64_t offset,
        const MyBufferClassPtr &buffer)
    {
        // The aiocb struct must be zeroed
        memset(&m_aiocb, 0, sizeof(struct aiocb));

        // Set what to do
        m_aiocb.aio_fildes = fildes;
        m_aiocb.aio_buf = buffer->data();
        m_aiocb.aio_nbytes = buffer->size();
        m_aiocb.aio_offset = offset;

        // Set notification
        m_aiocb.aio_sigevent.sigev_notify = SIGEV_SIGNAL;
        m_aiocb.aio_sigevent.sigev_signo = SIGUSR1;

        // ATTEMPT TO SET A VALUE THAT CAN BE READ IN THE HANDLER
        m_aiocb.aio_sigevent.sigev_value.sival_ptr = this;
    }

    struct aiocb* GetAiocbp()
    {
        return &m_aiocb;
    }

private:
    struct aiocb m_aiocb;
    // Some more context here
};

Then called from another place:

aio_context *ctx = new aio_context(file_descriptor, offset, data);
// set some more context here
int ret = aio_write(ctx->GetAiocbp());
if (0 != ret) {
    // throw something
}

My signal processing setup is as follows:

sigemptyset(&m_CurrentSIGHandler.sa_mask);
m_CurrentSIGHandler.sa_sigaction = aio_completion_handler;
m_CurrentSIGHandler.sa_flags = SA_SIGINFO;
sigaction(SIGUSR1, &m_CurrentSIGHandler, &m_PreviousSIGHandler);

and the actual handler:

void aio_completion_handler(int signo, siginfo_t *info, void *context)
{
    if (info->si_signo == SIGUSR1) {
        // Get the aio operation
        aio_context *ctx = static_cast<aio_context *>(info->si_value.sival_ptr);

        // THIS ASSERT ALWAYS FAILS - ctx IS NULL
        assert(ctx);

        // next check aio_error and aio_return using the aicb member of the ctx
        // ...
    }
}

So the problem is that si_value.sival_ptr is always NULL in the signal handler, instead of the aio_context pointer that I set in the aiocb structure. I must have misunderstood how to do this, so can someone tell me what I'm doing wrong?

MacOSX 10.6, ( ) 10.5, .

, , , , AIO - ?

Update:

- http://lists.apple.com/archives/darwin-dev/2008/Oct/msg00054.html.

http://www.opensource.apple.com/source/xnu/xnu-1504.9.26/bsd/kern/kern_aio.c, , , sigev_value . , , aio_ * Mac OS X. , , . - , aio_ * ?

Answer 1

Mac OS X ([RTS] posix), POSIX, . Mac OS X AIO. - , .