記憶體管理-swMemoryGlobal

jackbot發表於2019-09-05
記憶體

在swoole_init()中執行了這麼一句SwooleG.memory_pool = swMemoryGlobal_new(SW_GLOBAL_MEMORY_PAGESIZE, 1); 會返回一個swMemoryPool 的”介面實現“。這部分內容屬於記憶體管理。

typedef struct _swMemoryPool
{
    void *object;
    void* (*alloc)(struct _swMemoryPool *pool, uint32_t size);
    void (*free)(struct _swMemoryPool *pool, void *ptr);
    void (*destroy)(struct _swMemoryPool *pool);
} swMemoryPool;

swMemoryPool結構以指標的形式來表現“介面”。下面看swMemoryGlobal的具體實現。首先看結構定義

typedef struct _swMemoryGlobal_page
{
    struct _swMemoryGlobal_page *next;  //下一個page
    char memory[0];   //柔性陣列，指向申請的記憶體地址
} swMemoryGlobal_page;

typedef struct _swMemoryGlobal
{
    uint8_t shared;
    uint32_t pagesize; //每頁大小
    swLock lock;
    swMemoryGlobal_page *root_page; //根節點
    swMemoryGlobal_page *current_page; //尾節點
    uint32_t current_offset; //尾節點資料偏移量
} swMemoryGlobal;

很明顯是以連結串列的形式來組織的。看新建swMemoryGlobal

swMemoryPool* swMemoryGlobal_new(uint32_t pagesize, uint8_t shared)
{
    swMemoryGlobal gm, *gm_ptr;
    assert(pagesize >= SW_MIN_PAGE_SIZE);
    bzero(&gm, sizeof(swMemoryGlobal));

    gm.shared = shared;
    gm.pagesize = pagesize;

    swMemoryGlobal_page *page = swMemoryGlobal_new_page(&gm);
    if (page == NULL)
    {
        return NULL;
    }
    if (swMutex_create(&gm.lock, shared) < 0)
    {
        return NULL;
    }

    gm.root_page = page;

    gm_ptr = (swMemoryGlobal *) page->memory;
    gm.current_offset += sizeof(swMemoryGlobal);

    swMemoryPool *allocator = (swMemoryPool *) (page->memory + gm.current_offset);
    gm.current_offset += sizeof(swMemoryPool);

    allocator->object = gm_ptr;
    allocator->alloc = swMemoryGlobal_alloc;
    allocator->destroy = swMemoryGlobal_destroy;
    allocator->free = swMemoryGlobal_free;

    memcpy(gm_ptr, &gm, sizeof(gm));
    return allocator;
}

static swMemoryGlobal_page* swMemoryGlobal_new_page(swMemoryGlobal *gm)
{
    swMemoryGlobal_page *page = (gm->shared == 1) ? sw_shm_malloc(gm->pagesize) : sw_malloc(gm->pagesize);
    if (page == NULL)
    {
        return NULL;
    }
    bzero(page, gm->pagesize);
    page->next = NULL;

    if (gm->current_page != NULL)
    {
        gm->current_page->next = page;
    }

    gm->current_page = page;
    gm->current_offset = 0;

    return page;
}

在新建頁中，主要是申請記憶體，做一個連結串列的處理,其中需要注意的是。在swMemoryGlobal中需要注意的是current_offset的偏移量是sizeof(swMemoryPool)+sizeof(swMemoryPool)，也就是說明swMemoryPool和swMemoryPool的資訊儲存在page裡。

接下來看3個函式

static void *swMemoryGlobal_alloc(swMemoryPool *pool, uint32_t size)
{
    swMemoryGlobal *gm = pool->object;
    size = SW_MEM_ALIGNED_SIZE(size);
    gm->lock.lock(&gm->lock);
    if (size > gm->pagesize - sizeof(swMemoryGlobal_page))
    {
        swWarn("failed to alloc %d bytes, exceed the maximum size[%d]", size, gm->pagesize - (int) sizeof(swMemoryGlobal_page));
        gm->lock.unlock(&gm->lock);
        return NULL;
    }
    if (gm->current_offset + size > gm->pagesize - sizeof(swMemoryGlobal_page))
    {
        swMemoryGlobal_page *page = swMemoryGlobal_new_page(gm);
        if (page == NULL)
        {
            swWarn("swMemoryGlobal_alloc alloc memory error");
            gm->lock.unlock(&gm->lock);
            return NULL;
        }
        gm->current_page = page;
    }
    void *mem = gm->current_page->memory + gm->current_offset;
    gm->current_offset += size;
    gm->lock.unlock(&gm->lock);
    return mem;
}

static void swMemoryGlobal_free(swMemoryPool *pool, void *ptr)
{
    swWarn("swMemoryGlobal Allocator don't need to release");
}

static void swMemoryGlobal_destroy(swMemoryPool *poll)
{
    swMemoryGlobal *gm = poll->object;
    swMemoryGlobal_page *page = gm->root_page;
    swMemoryGlobal_page *next;

    do
    {
        next = page->next;
        sw_shm_free(page);
        page = next;
    } while (page);
}

不需要free、destroy從連結串列頭依此釋放記憶體。

alloc的規則也很簡單：a.申請的size超過規定，不給分配。 b.當前page剩餘量不夠，申請新個page來分配 c.當前page夠用，直接分配。

還有兩種記憶體分配，ring_buffer和fixed_pool，用到再說。

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