TA貢獻(xiàn)1772條經(jīng)驗(yàn) 獲得超5個(gè)贊
如果沒有對(duì)多線程做特殊處理的話，任何會(huì)帶來副作用的函數(shù)內(nèi)都可能導(dǎo)致這個(gè)問題。
給你舉個(gè)栗子：glibc的qsort函數(shù)在多線程使用的時(shí)候也可能會(huì)core。為什么呢？因?yàn)橛幸欢未a是這樣的
if (phys_pages == 0)
{
phys_pages = __sysconf (_SC_PHYS_PAGES);
//__sysconf函數(shù)在sysdeps/posix/sysconf.c中
//_SC_PHYS_PAGES對(duì)應(yīng)到函數(shù)__get_phys_pages()
//位于文件sysdeps/unix/sysv/linux/getsysstats.c中
//通過phys_pages_info()打開/proc/meminfo來讀取內(nèi)存信息
//(這就定位到了qsort打開文件的問題)
if (phys_pages == -1)
/* Error while determining the memory size. So let's
assume there is enough memory. Otherwise the
implementer should provide a complete implementation of the `sysconf' function. */
phys_pages = (long int) (~0ul >> 1);
/* The following determines that we will never use more than
a quarter of the physical memory. */
phys_pages /= 4;
pagesize = __sysconf (_SC_PAGESIZE);
}
//注意，上面這一段if會(huì)產(chǎn)生競(jìng)爭(zhēng)，出現(xiàn)線程安全安全：
//如果兩個(gè)線程都調(diào)用qsort，當(dāng)線程1獲取了phys_pages之后，線程2
//才到達(dá)if，線程2就會(huì)跳過這一段代碼，直接執(zhí)行下面的if語句——
//而此時(shí)pagesize尚未初始化（=0），于是就會(huì)出現(xiàn)除零錯(cuò)誤，導(dǎo)致
//core dump
/* Just a comment here. We cannot compute (phys_pages * pagesize) and compare the needed amount of memory against this value.
The problem is that some systems might have more physical
memory then can be represented with a `size_t' value (when
measured in bytes. */
/* If the memory requirements are too high don't allocate memory. */
//如果所需的內(nèi)存頁數(shù)大于總的可用內(nèi)存，則不分配內(nèi)存（防止swap降低性能）
if (size / pagesize > (size_t) phys_pages)
{
//直接使用stdlib/qsort.c中的 _quicksort 進(jìn)行排序
_quicksort (b, n, s, cmp, arg); return;
}
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