C中的内存分配测试-如何为malloc和free编写CUnit测试

Question

因为有几天我一直在为一个无法修复的应用程序进行测试。所以我决定为我的测试写一个测试。。。

我想分配记忆，看着使用中的记忆成长，然后再次释放记忆。我估计分配的内存不再使用了，对吧？

我正在开发Mac OSX（10.6.8）和gcc（gcc）4.2.1

所以我写了这个测试：

void testMemoryFreeCheck(){
    puts("- test Memory Free Check  -");
    puts("- ----------------------- -");
    puts("- This test takes a while -");
    puts("");
    struct rusage rus;
    getrusage(RUSAGE_SELF, &rus);
    // Things befor we want to mature. 
    char *holder[10000];
    char *bigHolder;
    int loops =  10000;
    int i;
    // Variables used for tests. 
    long int afterFirstTestKiloByte = 0;
    long int afterSecondTestKiloByte = 0;
    long int afterThirdTestKiloByte = 0;
    long int afterForuthTestKiloByte = 0;
    getrusage(RUSAGE_SELF, &rus);
    long int initialKiloByte = rus.ru_maxrss;
    printf("Initial KB Used: %ldn", initialKiloByte);
    // a adder to proof that we get it write
    char add = "A";
    getrusage(RUSAGE_SELF, &rus);
    long int afterAddKiloByte = rus.ru_maxrss;
    printf("After a char add KB Used: %ldn", initialKiloByte);
    getrusage(RUSAGE_SELF, &rus);
    long int growingKiloByte = rus.ru_maxrss;
    // This loop should do nothing.
    for(i=0; i<loops; ++i){
        printf(".");
    }
    puts("");
    getrusage(RUSAGE_SELF, &rus);
    afterFirstTestKiloByte = rus.ru_maxrss;
    printf("First Test should be 0 : %ldn", (afterFirstTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterFirstTestKiloByte - afterAddKiloByte) == 0);
    // This loop should free all allocated space.
    for(i=0; i<(loops * 128); ++i){
        char *tmp = malloc(1024 * 1024);
        free(tmp);
    }
    getrusage(RUSAGE_SELF, &rus);
    afterSecondTestKiloByte = rus.ru_maxrss;
    printf("Second Test should be 0 (4096 is ok for some reasons): %ldn", (afterSecondTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterSecondTestKiloByte - afterAddKiloByte) <= 4096);
    // This loop should increase the allocated space.
    for(i=0; i<loops; ++i){
        holder[i] = malloc(1024 * 1024);
    }
    getrusage(RUSAGE_SELF, &rus);
    afterThirdTestKiloByte = rus.ru_maxrss;
    printf("Third Test should be grater than 0 : %ldn", (afterThirdTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterThirdTestKiloByte - afterAddKiloByte) > 0);
    // now free the memmory and get back to the initial value
    for(i=0; i<loops; ++i){
        free(holder[i]);
    }  
    getrusage(RUSAGE_SELF, &rus);
    afterForuthTestKiloByte = rus.ru_maxrss;
    printf("Forth Test should be reset to 0 : %ldn", (afterForuthTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterThirdTestKiloByte - afterAddKiloByte) == 0);
    puts("- ----------------------- -");
}

我的输出是：

- test Memory Free Check  -
- ----------------------- -
- This test takes a while -
Initial KB Used: 458752
After a char add KB Used: 458752
[...]
First Test should be 0 : 0
Second Test should be 0 (4096 is ok for some reasons): 4096
Third Test should be grater than 0 : 1601536
Forth Test should be reset to 0 : 1601536
- ----------------------- -

我现在有两个问题无法解释：

1. 为什么第二个测试是4096而不是0
2. 为什么Forth测试没有0

第四次考试把我吓坏了。请看一看，也许你可以解释如何测试免费内存调用。我假设内存管理器不会杀死字节，而是重用它，所以内存会感染rus.ru_maxrss。但我该如何测试免费？

Answer 1

使用malloc分配的内存不会返回到操作系统，即使在free'd时也是如此。直到程序退出，内存才会返回到操作系统。

getrusage返回操作系统测量的程序正在使用的内存量。

结合以上信息，您就可以对这两个问题都有答案。