[RTT例程练习] 3.3 静态内存管理，内存池mempool
内存池是一种静态的内存管理方法。它预先将一块固定连续的内存区域划分成几个大小不同的块。使用者申请时就将对应大小的内存块给他。这种方法的优点是不会有内存碎片，但不够灵活，适用于需要频繁存取的场合，例如buffer。
这个例子有两个线程。thread1不停分配内存块，但其中并没有使用delay() 来使自己挂起，所以thread2 由于优先级低于 thread1 而一直得不到运行。thread1 分配完所有内存块以后，又试着再取得一个内存块，由于内存块已经被分配完，所以thread1 会因为得不到资源而被挂起。此时thread2 开始运行，释放内存块，释放了一个以后，thread1 的等待条件满足而执行了一次，然后thread2 继续运行直至结束。
程序：
#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++)
{
/* 申请内存块 */
rt_kprintf("allocate No.%d\n", i);
if (ptr[i] == RT_NULL)
{
ptr[i] = rt_mp_alloc(&mp, RT_WAITING_FOREVER);
}
}
/* 继续申请一个内存块，因为已经没有内存块，线程应该被挂起 */
block = rt_mp_alloc(&mp, RT_WAITING_FOREVER);
rt_kprintf("allocate the block mem\n");
/* 释放这个内存块 */
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 ++)
{
/* 释放所有分配成功的内存块 */
if (ptr[i] != RT_NULL)
{
rt_kprintf("release block %d\n", i);
rt_mp_free(ptr[i]);
ptr[i] = RT_NULL;
}
}
/* 休眠10个OS Tick */
rt_thread_delay(10);
}
}
int rt_application_init()
{
int i;
for (i = 0; i < 48; i ++) ptr[i] = RT_NULL;
/* 初始化内存池对象 ,每块分配的大小为80，但是另外还有大小为4的控制头，所以实际大小为84*/
rt_mp_init(&mp, "mp1", &mempool[0], sizeof(mempool), 80);
/* 创建线程1 */
tid1 = rt_thread_create("t1",
thread1_entry, RT_NULL, 512, 8, 10);
if (tid1 != RT_NULL)
rt_thread_startup(tid1);
/* 创建线程2 */
tid2 = rt_thread_create("t2",
thread2_entry, RT_NULL, 512, 9, 10);
if (tid2 != RT_NULL)
rt_thread_startup(tid2);
return 0;
}结果：
allocate No.0 allocate No.1 allocate No.2 allocate No.3 allocate No.4 allocate No.5 allocate No.6 allocate No.7 allocate No.8 allocate No.9 allocate No.10 allocate No.11 allocate No.12 allocate No.13 allocate No.14 allocate No.15 allocate No.16 allocate No.17 allocate No.18 allocate No.19 allocate No.20 allocate No.21 allocate No.22 allocate No.23 allocate No.24 allocate No.25 allocate No.26 allocate No.27 allocate No.28 allocate No.29 allocate No.30 allocate No.31 allocate No.32 allocate No.33 allocate No.34 allocate No.35 allocate No.36 allocate No.37 allocate No.38 allocate No.39 allocate No.40 allocate No.41 allocate No.42 allocate No.43 allocate No.44 allocate No.45 allocate No.46 allocate No.47 try to release block release block 0 allocate the block mem release block 1 release block 2 release block 3 release block 4 release block 5 release block 6 release block 7 release block 8 release block 9 release block 10 release block 11 release block 12 release block 13 release block 14 release block 15 release block 16 release block 17 release block 18 release block 19 release block 20 release block 21 release block 22 release block 23 release block 24 release block 25 release block 26 release block 27 release block 28 release block 29 release block 30 release block 31 release block 32 release block 33 release block 34 release block 35 release block 36 release block 37 release block 38 release block 39 release block 40 release block 41 release block 42 release block 43 release block 44 release block 45 release block 46 release block 47
