blocks|key|3977761|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3977762|调用unset()是否会释放与该对象关联的内存？|blockquote|3977763|3977764|3977765|是这样的。|offset|length|style|BOLD|3977766|使用memory_get_usage()自己检查|CODE|3977767|echo+memory_get_usage()+.+"<br+/>";
unset($array['key']);
unset($array['key2']);
unset($array['key3']);
echo+memory_get_usage();|code-block|syntax|javascript|3977768|更多资源：|3977769|3977770|Garbage+Collection+(Offical+Docs+but+for+5.3)|unordered-list-item|3977771|Be+wary+of+garbage+collection|3977772|3977773|从后面的链接引用：|3977774|3977775|+PHP在三个主要时刻执行垃圾收集：|3977776|3977777|3977778|当您离开function|3977779|When时告诉|3977780|ordered-list-item|3977781|脚本将结束|3977782|3977783|3977784|当您使用unset()、、mysql_free_result()或其他显式清除变量之后的资源销毁函数时，就会发生情况1。情况2隐含地清除了资源--任何离开作用域的变量，即不再适用的变量，都会被清除。最后，情景3隐式地释放了所有与脚本相关的资源。|3977785|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.memory-get-usage.php|1|http://php.net/manual/en/features.gc.php|2|http://www.tuxradar.com/practicalphp/18/1/10^0|0|0|0|0|0|5|0|2|I|2|I|0|0|0|0|5|0|0|0|19|1|0|0|T|2|0|0|8|1|0|0|0|0|0|0|0|0|0|0|0|4|8|0^^$0|@$1|2|3|-4|4|5|6|1X|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|1Y|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|1Z|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|20|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|21|7|@$H|22|I|23|J|K]]|8|@]|9|$]]|$1|L|3|M|4|5|6|24|7|@$H|25|I|26|J|N]]|8|@$H|27|I|28|1|29]]|9|$]]|$1|O|3|P|4|Q|6|2A|7|@]|8|@]|9|$R|S]]|$1|T|3|U|4|5|6|2B|7|@$H|2C|I|2D|J|K]]|8|@]|9|$]]|$1|V|3|-4|4|5|6|2E|7|@]|8|@]|9|$]]|$1|W|3|X|4|Y|6|2F|7|@]|8|@$H|2G|I|2H|1|2I]]|9|$]]|$1|Z|3|10|4|Y|6|2J|7|@]|8|@$H|2K|I|2L|1|2M]]|9|$]]|$1|11|3|-4|4|5|6|2N|7|@]|8|@]|9|$]]|$1|12|3|13|4|5|6|2O|7|@$H|2P|I|2Q|J|K]]|8|@]|9|$]]|$1|14|3|-4|4|5|6|2R|7|@]|8|@]|9|$]]|$1|15|3|16|4|C|6|2S|7|@]|8|@]|9|$]]|$1|17|3|-4|4|5|6|2T|7|@]|8|@]|9|$]]|$1|18|3|-4|4|5|6|2U|7|@]|8|@]|9|$]]|$1|19|3|1A|4|5|6|2V|7|@]|8|@]|9|$]]|$1|1B|3|1C|4|Y|6|2W|7|@]|8|@]|9|$]]|$1|1D|3|-4|4|1E|6|2X|7|@]|8|@]|9|$]]|$1|1F|3|1G|4|1E|6|2Y|7|@]|8|@]|9|$]]|$1|1H|3|-4|4|5|6|2Z|7|@]|8|@]|9|$]]|$1|1I|3|-4|4|5|6|30|7|@]|8|@]|9|$]]|$1|1J|3|1K|4|5|6|31|7|@$H|32|I|33|J|K]]|8|@]|9|$]]|$1|1L|3|-4|4|5|6|34|7|@]|8|@]|9|$]]]|1M|$1N|$4|1O|1P|1Q|9|$1R|1S]]|1T|$4|1O|1P|1Q|9|$1R|1U]]|1V|$4|1O|1P|1Q|9|$1R|1W]]]]

<blockquote>
 Does calling unset() free the memory
 that was associated with that object?
</blockquote>

Yes it does.

Check for yourself using <a href="http://php.net/manual/en/function.memory-get-usage.php" rel="nofollow noreferrer"><code>memory_get_usage()</code></a>:

<pre><code>echo memory_get_usage() . "&lt;br /&gt;";
unset($array['key']);
unset($array['key2']);
unset($array['key3']);
echo memory_get_usage();
</code></pre>

More Resources:

<ul>
<li><a href="http://php.net/manual/en/features.gc.php" rel="nofollow noreferrer">Garbage Collection (Offical Docs but for 5.3)</a></li>
<li><a href="http://www.tuxradar.com/practicalphp/18/1/10" rel="nofollow noreferrer">Be wary of garbage collection</a></li>
</ul>

Quoting from later link:

<blockquote>
 PHP performs garbage collection at
 three primary junctures:
 
 <ol>
 <li>When you tell it to</li>
 <li>When you leave a function</li>
 <li>When the script ends</li>
 </ol>
 
 Situation 1 occurs when you use
 unset(), mysql_free_result(), or other
 resource-destroying functions that
 explicitly clear up after your
 variables. Situation 2 clears up
 resources implicitly - any variable
 that leaves scope, i.e. is no longer
 applicable, gets cleared up for you.
 Finally, situation 3 frees up all
 script-related resources implicitly.
</blockquote>

blocks|key|2569664|text|unset()在php中确实“释放”内存，但它让垃圾收集器决定何时实际释放内存。因此，可以根据需要或方便的情况(在PHP耗尽可用内存之前)释放内存。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2569665|一个主要的警告是要注意，您不是试图在局部范围内unset()全局变量。当在函数的区域设置中执行此操作时，即使是通过引用传递的变量也只会有它们的本地引用unset。要真正使内存可用，任何unset()都应该在该变量的适当作用域内执行。|2569666|entityMap^0|0|7|0|N|7|23|5|2K|7|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|I|$]]

<code>unset()</code> does "free" memory in php, but it lets the garbage collector decide when to actually release said memory. Thus, memory is freed on an as-needed or as-convenient basis (prior to PHP running out of available memory).

A major caveat is to watch that you're not attempting to <code>unset()</code> global variables within a local scope. Even variables passed in by reference will only have their local references <code>unset</code> when this is performed in a function's locale. To truly make memory available, any <code>unset()</code> should be done in that variable's appropriate scope.

blocks|key|3977713|text|它不会立即释放内存，但它允许垃圾收集器这样做。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3977714|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It doesn't free the memory immediately, but it allows the garbage collector to do it.

blocks|key|2569741|text|通过取消设置一个变量，您可以将它的"refcount“设置为0。这允许Zend引擎在内存中移动东西，它知道它可以覆盖内存中的变量区域，因为它的refcount为0。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2569742|这在垃圾收集被考虑之前就已经发生了。至此，unset()确实在应用程序的生命周期中为您提供了帮助。|2569743|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

By unsetting a variable you're setting it's "refcount" to 0. This allows for the Zend Engine to shift things about in memory and it knows that it can overwrite your variables area in memory as it has a refcount of 0.

This occurs before garbage collection is even thought of. So there you have it, unset() does actually help you out during the lifecycle of your app.

blocks|key|2569772|text|不，它不一定会释放任何东西。它只是减少了引用计数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2569773|示例：|2569774|//object+has+reference+count+1+because+it+has+one+variable+referencing+1
$a+=+new+BigObject;
//object+still+has+reference+count+2,+but+no+new+object+was+allocated+in+memory
$b+=+$a;
//object+has+reference+count+1
unset($a);
//the+object+is+still+in+memory|code-block|syntax|javascript|2569775|吹毛求疵:从技术上讲，这里有两个引用计数--对象的引用计数和zval的引用计数。在整个程序中，对象的引用计数只有1，它实际上是在赋值和对unset的调用中更改的zval的引用计数。|offset|length|style|CODE|2569776|entityMap^0|0|0|0|1W|5|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

No, it doesn't necessarily free anything. It just decreases the reference count.

Example:

<pre><code>//object has reference count 1 because it has one variable referencing 1
$a = new BigObject;
//object still has reference count 2, but no new object was allocated in memory
$b = $a;
//object has reference count 1
unset($a);
//the object is still in memory
</code></pre>

Nitpick corner: technically, there are two reference counts in play here -- the object's and the zval's. The reference count of the object is only 1 throughout the program, it's actually the reference count of the zval that's changed in the assignment and in the call to <code>unset</code>.

blocks|key|3977862|text|在PHP+>5.3.0中，gc_collect_cycles()函数强制收集任何现有的垃圾循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3977863|entityMap|0|LINK|mutability|MUTABLE|url|http://uk.php.net/manual/en/function.gc-collect-cycles.php^0|D|J|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

In PHP >5.3.0, the <a href="http://uk.php.net/manual/en/function.gc-collect-cycles.php" rel="nofollow noreferrer">gc_collect_cycles()</a> function forces collection of any existing garbage cycles.

Does calling <code>unset()</code> free the memory that was associated with that object? There are a couple cases where I find myself handling large associative arrays and I would like to remove them when done (freeing up memory to create new ones).

Memory Issues with PHP (5)

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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调用unset()是否会释放与该对象关联的内存？有几种情况下，我发现自己在处理大型关联数组，并且我想在处理完后删除它们(释放内存以创建新的关联数组)。

问PHP的内存问题(5)
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回答 6

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