記憶體池是一種靜態的記憶體管理方法。它預先將一塊固定連續的記憶體區域劃分成幾個大小不同的塊。使用者申請時就將對應大小的記憶體塊給他。這種方法的優點是不會有記憶體碎片，但不夠靈活，適用於需要頻繁存取的場合，例如buffer。

這個例子有兩個執行緒。thread1不停分配記憶體塊，但其中並沒有使用delay() 來使自己掛起，所以thread2 由於優先順序低於 thread1 而一直得不到執行。thread1 分配完所有記憶體塊以後，又試著再取得一個記憶體塊，由於記憶體塊已經被分配完，所以thread1 會因為得不到資源而被掛起。此時thread2 開始執行，釋放記憶體塊，釋放了一個以後，thread1 的等待條件滿足而執行了一次，然後thread2 繼續執行直至結束。

程式：

#include <rtthread.h>

static rt_uint8_t *ptr[48];
static rt_uint8_t mempool[4096];
static struct rt_mempool mp;

static rt_thread_t tid1 = RT_NULL;
static rt_thread_t tid2 = RT_NULL;

static void thread1_entry(void* parameter)
{
    int i,j = 1;
    char *block;

    while(j--)
    {
        for (i = 0; i < 48; i++)
        {
            /* 申請記憶體塊 */
            rt_kprintf("allocate No.%d\n", i);
            if (ptr[i] == RT_NULL)
            {
                ptr[i] = rt_mp_alloc(&mp, RT_WAITING_FOREVER);
            }
        }

        /* 繼續申請一個記憶體塊，因為已經沒有記憶體塊，執行緒應該被掛起 */
        block = rt_mp_alloc(&mp, RT_WAITING_FOREVER);
        rt_kprintf("allocate the block mem\n");
        /* 釋放這個記憶體塊 */
        rt_mp_free(block);
        block = RT_NULL;
    }
}

static void thread2_entry(void *parameter)
{
    int i,j = 1;

    while(j--)
    {
        rt_kprintf("try to release block\n");

        for (i = 0 ; i < 48; i ++)
        {
            /* 釋放所有分配成功的記憶體塊 */
            if (ptr[i] != RT_NULL)
            {
                rt_kprintf("release block %d\n", i);

                rt_mp_free(ptr[i]);
                ptr[i] = RT_NULL;
            }
        }

        /* 休眠10個OS Tick */
        rt_thread_delay(10);
    }
}



int rt_application_init()
{
    int i;
    for (i = 0; i < 48; i ++) ptr[i] = RT_NULL;

    /* 初始化記憶體池物件 ,每塊分配的大小為80，但是另外還有大小為4的控制頭，所以實際大小為84*/
    rt_mp_init(&mp, "mp1", &mempool[0], sizeof(mempool), 80);

    /* 建立執行緒1 */
    tid1 = rt_thread_create("t1",
        thread1_entry, RT_NULL, 512, 8, 10);
    if (tid1 != RT_NULL)
        rt_thread_startup(tid1);

    /* 建立執行緒2 */
    tid2 = rt_thread_create("t2",
    thread2_entry, RT_NULL, 512, 9, 10);
    if (tid2 != RT_NULL)
        rt_thread_startup(tid2);

    return 0;
}
 

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