关于例程中邮箱相关问题

发布于 2021-07-07 23:41:42 浏览：813 订阅该版

```c
/* 
 * Copyright (c) 2006-2018, RT-Thread Development Team 
 * 
 * SPDX-License-Identifier: Apache-2.0 
 * 
 * Change Logs: 
 * Date           Author       Notes 
 * 2018-08-24     yangjie      the first version 
 */

/*
 * 程序清单：邮箱例程
 *
 * 这个程序会创建2个动态线程，一个静态的邮箱对象，其中一个线程往邮箱中发送邮件，
 * 一个线程往邮箱中收取邮件。
 */
#include <rtthread.h>

#define THREAD_PRIORITY      10
#define THREAD_TIMESLICE     5

/* 邮箱控制块 */
static struct rt_mailbox mb;
/* 用于放邮件的内存池 */
static char mb_pool[128];

static char mb_str1[] = "I'm a mail!";
static char mb_str2[] = "this is another mail!";
static char mb_str3[] = "over";

ALIGN(RT_ALIGN_SIZE)
static char thread1_stack[1024];
static struct rt_thread thread1;

/* 线程1入口 */
static void thread1_entry(void *parameter)
{
    char *str;

while (1)
    {
        rt_kprintf("thread1: try to recv a mail\n");

/* 从邮箱中收取邮件 */
        if (rt_mb_recv(&mb, (rt_uint32_t *)&str, RT_WAITING_FOREVER) == RT_EOK)
        {					
            rt_kprintf("thread1: get a mail from mailbox, the content:%s\n", str);
					
						rt_kprintf("entry is %d,in_offset is %d,out_offset if %d\n",mb.entry,mb.in_offset,mb.out_offset);
					
            if (str == mb_str3)
                break;

/* 延时100ms */
            rt_thread_mdelay(300);
        }
    }
    /* 执行邮箱对象脱离 */
    rt_mb_detach(&mb);
}

ALIGN(RT_ALIGN_SIZE)
static char thread2_stack[1024];
static struct rt_thread thread2;

/* 线程2入口 */
static void thread2_entry(void *parameter)
{
    rt_uint8_t count;

count = 0;
    while (count < 20)
    {
        count ++;
        if (count & 0x1)
        {
            /* 发送mb_str1地址到邮箱中 */
            rt_mb_send(&mb, (rt_uint32_t)&mb_str1);
        }
        else
        {
            /* 发送mb_str2地址到邮箱中 */
            rt_mb_send(&mb, (rt_uint32_t)&mb_str2);
        }
				
				rt_kprintf("entry is %d,in_offset is %d,out_offset if %d\n",mb.entry,mb.in_offset,mb.out_offset);

/* 延时200ms */
        rt_thread_mdelay(20);
    }

/* 发送邮件告诉线程1，线程2已经运行结束 */
    rt_mb_send(&mb, (rt_uint32_t)&mb_str3);
}

int mailbox_sample(void)
{
    rt_err_t result;

/* 初始化一个mailbox */
    result = rt_mb_init(&mb,
                        "mbt",                      /* 名称是mbt */
                        &mb_pool[0],                /* 邮箱用到的内存池是mb_pool */
                        sizeof(mb_pool) / 4,        /* 邮箱中的邮件数目，因为一封邮件占4字节 */
                        RT_IPC_FLAG_FIFO);          /* 采用FIFO方式进行线程等待 */
    if (result != RT_EOK)
    {
        rt_kprintf("init mailbox failed.\n");
        return -1;
    }
		
    rt_thread_init(&thread1,
                   "thread1",
                   thread1_entry,
                   RT_NULL,
                   &thread1_stack[0],
                   sizeof(thread1_stack),
                   THREAD_PRIORITY, THREAD_TIMESLICE);
    rt_thread_startup(&thread1);

rt_thread_init(&thread2,
                   "thread2",
                   thread2_entry,
                   RT_NULL,
                   &thread2_stack[0],
                   sizeof(thread2_stack),
                   THREAD_PRIORITY, THREAD_TIMESLICE);
    rt_thread_startup(&thread2);
    return 0;
}

/* 导出到 msh 命令列表中 */
MSH_CMD_EXPORT(mailbox_sample, mailbox sample);
```

```

\ | /
- RT -     Thread Operating System
 / | \     3.1.0 build Jul  7 2021
 2006 - 2018 Copyright by rt-thread team
msh >mai
mailbox_sample
msh >mailbox_sample
thread1: try to recv a mail
entry is 1,in_offset is 1,out_offset if 0
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 0,in_offset is 1,out_offset if 1
msh >entry is 1,in_offset is 2,out_offset if 1
entry is 2,in_offset is 3,out_offset if 1
entry is 3,in_offset is 4,out_offset if 1
entry is 4,in_offset is 5,out_offset if 1
entry is 5,in_offset is 6,out_offset if 1
entry is 6,in_offset is 7,out_offset if 1
entry is 7,in_offset is 8,out_offset if 1
entry is 8,in_offset is 9,out_offset if 1
entry is 9,in_offset is 10,out_offset if 1
entry is 10,in_offset is 11,out_offset if 1
entry is 11,in_offset is 12,out_offset if 1
entry is 12,in_offset is 13,out_offset if 1
entry is 13,in_offset is 14,out_offset if 1
entry is 14,in_offset is 15,out_offset if 1
entry is 15,in_offset is 16,out_offset if 1
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 14,in_offset is 16,out_offset if 2
entry is 15,in_offset is 17,out_offset if 2
entry is 16,in_offset is 18,out_offset if 2
entry is 17,in_offset is 19,out_offset if 2
entry is 18,in_offset is 20,out_offset if 2
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 18,in_offset is 21,out_offset if 3
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 17,in_offset is 21,out_offset if 4
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 16,in_offset is 21,out_offset if 5
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 15,in_offset is 21,out_offset if 6
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 14,in_offset is 21,out_offset if 7
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 13,in_offset is 21,out_offset if 8
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 12,in_offset is 21,out_offset if 9
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 11,in_offset is 21,out_offset if 10
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 10,in_offset is 21,out_offset if 11
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 9,in_offset is 21,out_offset if 12
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 8,in_offset is 21,out_offset if 13
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 7,in_offset is 21,out_offset if 14
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 6,in_offset is 21,out_offset if 15
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 5,in_offset is 21,out_offset if 16
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 4,in_offset is 21,out_offset if 17
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 3,in_offset is 21,out_offset if 18
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:I'm a mail!
entry is 2,in_offset is 21,out_offset if 19
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:this is another mail!
entry is 1,in_offset is 21,out_offset if 20
thread1: try to recv a mail
thread1: get a mail from mailbox, the content:over
entry is 0,in_offset is 21,out_offset if 21

```

以上是我将例程的mailbox_sample进行了修改,对于输出,我有以下几个疑问:
1.邮件的发送和收取的对应关系,比如我按顺序发送了1,2,3封邮件,然后进行接收,接收顺序是1,2,3吗?
2.控制块里的entry,in_offset,out_offset的物理意义是什么?in_offset,out_offset为什么会一直增加?会不会清零?
3.如果发送邮件超出预先定义的内存大小会发生什么情况?