#include <unistd.h>
#include <assert.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/select.h>
#include <signal.h>
#include <stdio.h>

void child(int writefd)
{
    ptrace(PTRACE_TRACEME, 0, 0, 0);
    raise(SIGSTOP);
    assert(write(writefd, "x", 1) == 1);
    raise(SIGSTOP);
}

void parent(pid_t child, int readfd)
{
    int status;
    assert(waitpid(child, &status, 0) == child);
    assert(WIFSTOPPED(status));
    assert(WSTOPSIG(status) == SIGSTOP);
    fd_set set;
    struct timeval tv;
    FD_ZERO(&set);
    FD_SET(readfd, &set);
    tv.tv_sec = 0;
    tv.tv_usec = 0;
    assert(select(readfd+1, &set, 0, 0, &tv) == 0);
    FD_ZERO(&set);
    FD_SET(readfd, &set);
    tv.tv_sec = 0;
    tv.tv_usec = 0;

    assert(ptrace(PTRACE_CONT, child, 0, 0) == 0);
    assert(waitpid(child, &status, 0) == child);
    assert(select(readfd+1, &set, 0, 0, &tv) == 1);
    kill(child, SIGKILL);
    assert(close(readfd) == 0);
    assert(waitpid(child, &status, 0) == child);
    assert(WIFSIGNALED(status));
    assert(WTERMSIG(status) == SIGKILL);
}

int main(int argc)
{
    int pipefd[2];
    int i = 0;
    for (;;)
    {
        ++i;
        if (!(i%10))
            printf("%d\n", i);
        assert(openpty(pipefd+0, pipefd+1, 0, 0) == 0);
//        assert(pipe(pipefd) == 0);
        pid_t pid = fork();
        assert(pid != -1);
        if (pid == 0)
        {
            assert(close(pipefd[0]) == 0);
            child(pipefd[1]);
            return 1;
        }
        else
        {
            assert(close(pipefd[1]) == 0);
            parent(pid, pipefd[0]);
        }
    }
    return 0;
}