15、异步I/O与I/O调度器：提升系统性能的关键

异步I/O与I/O调度器：提升系统性能的关键

1. 异步I/O

异步I/O的执行需要底层的内核支持。POSIX 1003.1 - 2003定义了aio接口，Linux系统实现了这些接口。aio库提供了一系列函数，用于提交异步I/O操作并在操作完成时接收通知：

#include <aio.h>
/* asynchronous I/O control block */
struct aiocb {
        int aio_fildes;               /* file descriptor */
        int aio_lio_opcode;           /* operation to perform */
        int aio_reqprio;              /* request priority offset */
        volatile void *aio_buf;       /* pointer to buffer */
        size_t aio_nbytes;            /* length of operation */
        struct sigevent aio_sigevent; /* signal number and value */
        /* internal, private members follow... */
};
int aio_read (struct aiocb *aiocbp);
int aio_write (struct aiocb *aiocbp);
int aio_error (c