Android内存使用——垃圾回收LOG，GC_CONCURRENT等的意义的说明
在调试程序的时候，经常发现GC_CONCURRENT之类的打印。在网上搜了一下，感觉说法各式各样。最后，在Google的官方网站上发现了详细介绍。
Every time a garbage collection occurs, logcat prints a message with the following information:
D/dalvikvm: <GC_Reason> <Amount_freed>, <Heap_stats>, <External_memory_stats>, <Pause_time>
- GC Reason
- What triggered the garbage collection and what kind of collection it is. Reasons that may appearinclude:
GC_CONCURRENT- A concurrent garbage collection that frees up memory as your heap begins to fill up.
GC_FOR_MALLOC- A garbage collection caused because your app attempted to allocate memory when your heap wasalready full, so the system had to stop your app and reclaim memory.
GC_HPROF_DUMP_HEAP- A garbage collection that occurs when you create an HPROF file to analyze your heap.
GC_EXPLICIT- An explicit garbage collection, such as when you call
gc()(which youshould avoid calling and instead trust the garbage collector to run when needed). GC_EXTERNAL_ALLOC- This happens only on API level 10 and lower (newer versions allocate everything in the Dalvikheap). A garbage collection for externally allocated memory (such as the pixel data stored innative memory or NIO byte buffers).
- Amount freed
- The amount of memory reclaimed from this garbage collection.
- Heap stats
- Percentage free and (number of live objects)/(total heap size).
- External memory stats
- Externally allocated memory on API level 10 and lower (amount of allocated memory) / (limit atwhich collection will occur).
- Pause time
- Larger heaps will have larger pause times. Concurrent pause times show two pauses: one at thebeginning of the collection and another near the end.
For example:
D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/9991K, external 4703K/5261K, paused 2ms+2ms
GC Reason：引起GC回收的原因。包括a)GC_CONCURRENT：我的理解是当你的堆快被用完的时候，就会触发这个GC回收。b)堆已经满了，同时又要试图分配新的内存，所以系统要回收内存。c）GC_HPROF_DUMP_HEAP这是做HPROF分析用的，正常情况下不会有的。d）这个是明确调用gc产出的垃圾回收。e）GC_EXTERNAL_ALLOC这个在2.3版本以后已经废弃了。所以不用关心了。
Amount freed：本次垃圾回收释放出来的内存。
Heap stats：当前空闲内存占总内存的百分比。比如下面的例子总的65%就是说有65%的空闲。二后面的3571K是占用了这么多，9991K是总的内存。这两个值相除，就是占用的百分比，加上前面的65%正好是100%。
External memory stats：2.3之后就废弃了。
Pause time：你的应用暂停的时间。
假如3571K/9991K 这个值不断增加，从来不减少，则可能有内存泄漏的问题。
