在調試程序的時候，經常發現GC_CONCURRENT之類的打印。在網上搜了一下，感覺說法各式各樣。最後，在Google的官方網站上發現了詳細介紹。
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 appear include:
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 was already 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 you should 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 Dalvik heap). A garbage collection for externally allocated memory (such as the pixel data stored in native 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 at which collection will occur).
- Pause time
- Larger heaps will have larger pause times. Concurrent pause times show two pauses: one at the beginning 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：我的理解是當你的堆快被用完的時候，就會觸發這個GC回收。b)堆已經滿了，同時又要試圖分配新的內存，所以系統要回收內存。c）GC_HPROF_DUMP_HEAP這是做HPROF分析用的，正常情況下不會有的。d）這個是明確調用gc產出的垃圾回收。e）GC_EXTERNAL_ALLOC這個在2.3版本以後已經廢棄了。所以不用關心了。
Amount freed：本次垃圾回收釋放出來的內存。
Heap stats：當前空閒內存佔總內存的百分比。比如下面的例子總的65%就是說有65%的空閒。二後面的3571K是佔用了這麼多，9991K是總的內存。這兩個值相除，就是佔用的百分比，加上前面的65%正好是100%。
External memory stats：2.3之後就廢棄了。
Pause time：你的應用暫停的時間。
假如3571K/9991K 這個值不斷增加，從來不減少，則可能有內存泄漏的問題。