【一起来玩RTOS系列】之RT-Thread 信号量用于资源计数

bigfanofloT · 发表于 2017-12-2 12:39:09

本帖最后由 bigfanofloT 于 2017-12-2 12:42 编辑

资源计数适合于线程间速度不匹配的场合，这个时候信号量可以做为前一线程工作完成的计数，而当调度到后一线程时，它可以以一种连续的方式一次处理数个事件。例如，生产者与消费者问题中，生产者可以对信号进行多次释放，而后消费者被调度到时能够一次处理多个资源。
注：一般资源计数类型多是混合方式的线程间同步，因为对于单个的资源处理依然存在线程的多重访问，这就需要对一个单独的资源进行访问、处理，并进行锁方式的互斥操作。

生产者消费者问题（英语：Producer-consumer problem），也称有限缓冲问题（英语：Bounded-buffer problem），是一个多线程同步问题的经典案例。该问题描述了两个共享固定大小缓冲区的线程——即所谓的“生产者”和“消费者”——在实际运行时会发生的问题。生产者的主要作用是生成一定量的数据放到缓冲区中，然后重复此过程。与此同时，消费者也在缓冲区消耗这些数据。该问题的关键就是要保证生产者不会在缓冲区满时加入数据，消费者也不会在缓冲区中空时消耗数据。
解决办法
要解决该问题，就必须让生产者在缓冲区满时休眠（要么干脆就放弃数据），等到下次消费者消耗缓冲区中的数据的时候，生产者才能被唤醒，开始往缓冲区添加数据。同样，也可以让消费者在缓冲区空时进入休眠，等到生产者往缓冲区添加数据之后，再唤醒消费者。通常采用进程间通信的方法解决该问题，常用的方法有信号灯法等。如果解决方法不够完善，则容易出现死锁的情况。出现死锁时，两个线程都会陷入休眠，等待对方唤醒自己。该问题也能被推广到多个生产者和消费者的情形。

接下来在机智云 gokit开发板上演示如何创建并使用信号量作为锁来进行资源的互斥访问，程序中semaphore是作为一种锁的形式存在，当要访问临界资源时，通过持有semaphore 的形式阻止其他线程进入。生产者线程负责生产产品，生产的产品放入缓冲区，当缓冲区满了时，生产者暂停生产，等待消费者消费缓冲区中的产品再重新启动。生产者生产产品前，需要确保缓冲区不满。消费者线程负责消费缓冲区中的产品，当缓冲区为空时，消费者暂停消费，等生产者向缓冲区中放入新的产品后再重新启动。消费者消费产品之前，需要确保缓冲区不为空。

/**
***********************************
* File Name : main.c
* Description : Main program body
***********************************
** This notice applies to any and all portions of this file
* that are not between comment pairs USER CODE BEGIN and
* USER CODE END. Other portions of this file, whether
* inserted by the user or by software development tools
* are owned by their respective copyright owners.
*
* COPYRIGHT(c) 2017 STMicroelectronics
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* 3. Neither the name of STMicroelectronics nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
***********************************
*/
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "STM32f1xx_hal.h"
#include "usart.h"
#include "gpio.h"
/* USER CODE BEGIN Includes */
#include "rtthread.h"
#include "string.h"
/* USER CODE END Includes */
/* Private variables ---------------------------------------------------------*/
/* USER CODE BEGIN PV */
/* Private variables ---------------------------------------------------------*/
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */
/* Private function prototypes -----------------------------------------------*/
/* USER CODE END PFP */
/* USER CODE BEGIN 0 */
//重映射串口1到rt_kprintf
void rt_hw_console_output(const char *str)
{
/* empty console output */
char aa='\r';
rt_enter_critical();
while(*str!='\0')
{
if(*str=='\n')
{
HAL_UART_Transmit(&huart1, (uint8_t *)&aa, 1, 10);
}
HAL_UART_Transmit(&huart1, (uint8_t *)(str++), 1, 10);
}
rt_exit_critical();
}
void rt_hw_us_delay(int us)
{
rt_uint32_t delta;
/* 获得延时经过的tick数 */
us = us * (SysTick->LOAD/(1000000/RT_TICK_PER_SECOND));
/* 获得当前时间 */
delta = SysTick->VAL;
/* 循环获得当前时间，直到达到指定的时间后退出循环 */
while (delta - SysTick->VAL< us);
}
void rt_hw_ms_delay(int ms)
{
int i=0,j=0;
for(j=0;j<ms;j++)
{
for (i=0;i<2;i++)
rt_hw_us_delay(500);
}
}
/*
* 程序清单：生产者消费者例子
*
* 这个例子中将创建两个线程用于实现生产者消费者问题
*/
#include <rtthread.h>
/* 定义最大5个元素能够被产生 */
#define MAXSEM 5
/* 用于放置生产的整数数组 */
rt_uint32_t array[MAXSEM];
/* 指向生产者、消费者在array数组中的读写位置 */
static rt_uint32_t set, get;
/* 指向线程控制块的指针 */
static rt_thread_t producer_tid = RT_NULL;
static rt_thread_t consumer_tid = RT_NULL;
struct rt_semaphore sem_lock;
struct rt_semaphore sem_empty, sem_full;
/* 生产者线程入口 */
void producer_thread_entry(void* parameter)
{
rt_int32_t cnt = 0;
/* 运行100次 */
while( cnt < 100)
{
/* 获取一个空位 */
rt_sem_take(&sem_empty, RT_WAITING_FOREVER);
/* 修改array内容，上锁 */
rt_sem_take(&sem_lock, RT_WAITING_FOREVER);
array[set%MAXSEM] = cnt + 1;
rt_kprintf("the producer generates a number: %d\n",
array[set%MAXSEM]);
set++;
rt_sem_release(&sem_lock);
/* 发布一个满位 */
rt_sem_release(&sem_full);
cnt++;
/* 暂停一段时间 */
rt_thread_delay(50);
}
rt_kprintf("the producer exit!\n");
}
/* 消费者线程入口 */
void consumer0_thread_entry(void* parameter)
{
rt_uint32_t no;
rt_uint32_t sum = 0;
/* 第0个线程 */
no = 0;
while(1)
{
/* 获取一个满位 */
rt_sem_take(&sem_full, RT_WAITING_FOREVER);
/* 临界区，上锁进行操作 */
rt_sem_take(&sem_lock, RT_WAITING_FOREVER);
sum += array[get%MAXSEM];
rt_kprintf("the consumer[%d] get a number:%d\n", no, array[get%MAXSEM]);
get++;
rt_sem_release(&sem_lock);
/* 释放一个空位 */
rt_sem_release(&sem_empty);
/* 生产者生产到100个数目，停止，消费者线程相应停止 */
if (get == 100) break;
/* 暂停一小会时间 */
rt_thread_delay(10);
}
rt_kprintf("the consumer[%d] sum is %d \n ", no, sum);
rt_kprintf("the consumer[%d] exit!\n",no);
}
/* 消费者线程入口 */
void consumer1_thread_entry(void* parameter)
{
rt_uint32_t no;
rt_uint32_t sum = 0;
/* 第1个线程 */
no = 1;
while(1)
{
/* 获取一个满位 */
rt_sem_take(&sem_full, RT_WAITING_FOREVER);
/* 临界区，上锁进行操作 */
rt_sem_take(&sem_lock, RT_WAITING_FOREVER);
sum += array[get%MAXSEM];
rt_kprintf("the consumer[%d] get a number:%d\n", no, array[get%MAXSEM]);
get++;
rt_sem_release(&sem_lock);
/* 释放一个空位 */
rt_sem_release(&sem_empty);
/* 生产者生产到100个数目，停止，消费者线程相应停止 */
if (get == 100) break;
/* 暂停一小会时间 */
rt_thread_delay(10);
}
rt_kprintf("the consumer[%d] sum is %d \n ", no, sum);
rt_kprintf("the consumer[%d] exit!\n",no);
}
/* 消费者线程入口 */
void consumer2_thread_entry(void* parameter)
{
rt_uint32_t no;
rt_uint32_t sum = 0;
/* 第2个线程 */
no = 2;
while(1)
{
/* 获取一个满位 */
rt_sem_take(&sem_full, RT_WAITING_FOREVER);
/* 临界区，上锁进行操作 */
rt_sem_take(&sem_lock, RT_WAITING_FOREVER);
sum += array[get%MAXSEM];
rt_kprintf("the consumer[%d] get a number:%d\n", no, array[get%MAXSEM]);
get++;
rt_sem_release(&sem_lock);
/* 释放一个空位 */
rt_sem_release(&sem_empty);
/* 生产者生产到100个数目，停止，消费者线程相应停止 */
if (get == 100) break;
/* 暂停一小会时间 */
rt_thread_delay(10);
}
rt_kprintf("the consumer[%d] sum is %d \n ", no, sum);
rt_kprintf("the consumer[%d] exit!\n",no);
}
int semaphore_producer_consumer_init()
{
/* 初始化3个信号量 */
rt_sem_init(&sem_lock , "lock", 1, RT_IPC_FLAG_FIFO);
rt_sem_init(&sem_empty,"empty", MAXSEM, RT_IPC_FLAG_FIFO);
rt_sem_init(&sem_full , "full", 0, RT_IPC_FLAG_FIFO);
/* 创建线程1 */
producer_tid = rt_thread_create("producer",
producer_thread_entry, /* 线程入口是producer_thread_entry */
RT_NULL, /* 入口参数是RT_NULL */
512, 1, 20);
if (producer_tid != RT_NULL)
rt_thread_startup(producer_tid);
/* 创建线程2 */
consumer_tid = rt_thread_create("consumer0",
consumer0_thread_entry,/* 线程入口是consumer_thread_entry */
RT_NULL, /* 入口参数是RT_NULL */
512, 3, 20);
if (consumer_tid != RT_NULL)
rt_thread_startup(consumer_tid);
/* 创建线程3 */
consumer_tid = rt_thread_create("consumer1",
consumer1_thread_entry,/* 线程入口是consumer_thread_entry */
RT_NULL, /* 入口参数是RT_NULL */
512, 3, 20);
if (consumer_tid != RT_NULL)
rt_thread_startup(consumer_tid);
/* 创建线程4 */
consumer_tid = rt_thread_create("consumer1",
consumer2_thread_entry,/* 线程入口是consumer_thread_entry */
RT_NULL, /* 入口参数是RT_NULL */
512, 3, 20);
if (consumer_tid != RT_NULL)
rt_thread_startup(consumer_tid);
return 0;
}
/* USER CODE END 0 */
int main(void)
{
/* USER CODE BEGIN 1 */
/* USER CODE END 1 */
/* MCU Configuration----------------------------------------------------------*/
// /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
// HAL_Init();
// /* USER CODE BEGIN Init */
// /* USER CODE END Init */
// /* Configure the system clock */
// SystemClock_Config();
// /* USER CODE BEGIN SysInit */
// /* USER CODE END SysInit */
// /* Initialize all configured peripherals */
// MX_GPIO_Init();
// MX_USART1_UART_Init();
/* USER CODE BEGIN 2 */
semaphore_producer_consumer_init();
printf("\r\n机智云只为智能硬件而生\r\n");
printf("Gizwits Smart Cloud for Smart Products\r\n");
printf("链接|增值|开放|中立|安全|自有|自由|生态\r\n");
printf("www.gizwits.com\r\n");
printf("\r\nGokit RT-Thread Demo\r\n\r\n");
return 0;
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
// while (1)
// {
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
//
// }
/* USER CODE END 3 */
}
/** System Clock Configuration
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct;
RCC_ClkInitTypeDef RCC_ClkInitStruct;
/**Initializes the CPU, AHB and APB busses clocks
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
/**Initializes the CPU, AHB and APB busses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
/**Configure the Systick interrupt time
*/
HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
/**Configure the Systick
*/
HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);
/* SysTick_IRQn interrupt configuration */
HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
}
/* USER CODE BEGIN 4 */
/* USER CODE END 4 */
/**
* @brief This function is executed in case of error occurrence.
* @param None
* @retval None
*/
void _Error_Handler(char * file, int line)
{
/* USER CODE BEGIN Error_Handler_Debug */
/* User can add his own implementation to report the HAL error return state */
while(1)
{
}
/* USER CODE END Error_Handler_Debug */
}
#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t* file, uint32_t line)
{
/* USER CODE BEGIN 6 */
/* User can add his own implementation to report the file name and line number,
ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
/* USER CODE END 6 */
}
#endif
/**
* @}
*/
/**
* @}
*/
/*********** (C) COPYRIGHT STMicroelectronics ***END OF FILE**/

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串口打印信息如下：

源码下载：

Gokit_RT-Thread.zip (8.7 MB, 下载次数: 2, 售价: 1 金钱)