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Home Backend Development PHP Tutorial PHP內(nèi)核(1)內(nèi)存管理

PHP內(nèi)核(1)內(nèi)存管理

Jun 13, 2016 pm 12:28 PM
limit memory php zend

PHP內(nèi)核(一)內(nèi)存管理

本文鏈接:http://www.orlion.ml/tag/php-internal/

一、內(nèi)存管理基礎(chǔ)

用c語言開發(fā)時(shí),開發(fā)者要手動(dòng)進(jìn)行內(nèi)存管理。PHP經(jīng)常作為web服務(wù)器的模塊,內(nèi)存管理與預(yù)防內(nèi)存泄露緊密關(guān)聯(lián)。另外PHP可能用于線程環(huán)境中,所以全局變量可能導(dǎo)致競(jìng)爭情況。此外Zend引擎面對(duì)一個(gè)十分特殊的使用模式:在一段比較短的時(shí)間內(nèi),許多zval結(jié)構(gòu)大小的內(nèi)存塊和其他的小內(nèi)存塊被申請(qǐng)又再被釋放,PHP的內(nèi)存管理也很重視memory_limit(內(nèi)存限制)

為了滿足以上的需求,Zend引擎提供了為了處理請(qǐng)求相關(guān)數(shù)據(jù)提供了一種特殊的內(nèi)存管理器。請(qǐng)求相關(guān)數(shù)據(jù)是指只需要服務(wù)于單個(gè)請(qǐng)求,最遲在請(qǐng)求結(jié)束時(shí)釋放的數(shù)據(jù)。擴(kuò)展開發(fā)者主要接觸下表中列出的慣例,雖然一些所提供的便捷功能使用宏實(shí)現(xiàn)的,但是本文中會(huì)像函數(shù)一樣對(duì)待。

如上所述,防止有內(nèi)存泄露并盡可能快的釋放所有內(nèi)存是內(nèi)存管理的重要組成部分。因?yàn)榘踩?,在?qǐng)求結(jié)束時(shí),Zend引擎會(huì)釋放所有由上面提到的API所分配的內(nèi)存。如果PHP使用--enable-debug配置選項(xiàng)進(jìn)行構(gòu)建,這將產(chǎn)生一個(gè)警告

當(dāng)使用PHP變量時(shí),需要確認(rèn)變量的內(nèi)存要使用emalloc來分配,并注意引用計(jì)數(shù)。

內(nèi)存泄漏檢測(cè)僅可以發(fā)現(xiàn)由 emalloc 分配內(nèi)存塊導(dǎo)致的泄漏。為進(jìn)行深層分析,建議使用內(nèi)存檢測(cè)器,如 valgrind 或 libumem 等。要簡化此分析,可在 PHP 啟動(dòng)時(shí)通過設(shè)置環(huán)境變量 USE_ZEND_ALLOC=0 來禁用 PHP 的內(nèi)存管理器。

(以上是PHP官網(wǎng)中文內(nèi)容)

二、數(shù)據(jù)持久化

數(shù)據(jù)持久化意味著任何數(shù)據(jù)預(yù)計(jì)比當(dāng)前請(qǐng)求生存時(shí)間長,沒有Zend引擎的內(nèi)存管理器非常關(guān)注于請(qǐng)求綁定分配,但是這通常不是實(shí)用或者是合適的。持久化內(nèi)存有時(shí)需要為了滿足外部類庫的要求,它也是有用的"黑科技"。

持久化內(nèi)存通常用在持久化數(shù)據(jù)庫連接上,雖然實(shí)踐起來并不好,但依然是最常使用的特性。

注意:下面所有函數(shù)采取額外的持久化參數(shù)應(yīng)該是false,引擎將用常規(guī)的分配器(emalloc),內(nèi)存不應(yīng)該是?considered persistent(不會(huì)翻譯!)。作為持久化的內(nèi)存,系統(tǒng)調(diào)用分配器,正像主要的內(nèi)存API一樣在大多數(shù)情況下它們?nèi)匀徊环祷乜罩羔?/p>

警告:需要注意被分配用來持久化的內(nèi)存不是最優(yōu)化的或者是被Zend引擎跟蹤的,它不被memory_limit所限制,另外,所有通過the hacker創(chuàng)建的變量一定不能被用來持久化內(nèi)存。

(翻譯的真爛!)

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