Allocation Failure happens when there isn’t enough free space to create new objects in Young generation. Allocation failures triggers Young GC.
On Linux, the JVM can trigger a GC if the kernel notifies there isn’t much memory left via mem_notify.
- 触发GC类型：Young GC。
GCLocker Initiated GC
The GC locker prevents GC from occurring when JNI code is in a critical region. If GC is needed while a thread is in a critical region, then it will allow them to complete, i.e. call the corresponding release function. Other threads will not be permitted to enter a critical region. Once all threads are out of critical regions a GC event will be triggered.
- 产生原因：如果线程执行在JNI临界区时，刚好需要进行GC，此时GC locker将会阻止GC的发生，同时阻止其他线程进入JNI临界区，直到最后一个线程退出临界区时触发一次GC。
- 触发GC类型：GCLocker Initiated GC。
Promotion Failure happens when there is no continuous memory space to promote larger object, even though total free memory is large enough. This is problem is called as heap fragmentation. Promotion Failure typically triggers Full GC.
- 触发GC类型：Full GC。
Concurrent Mode Failure
The CMS collector uses one or more garbage collector threads that run simultaneously with the application threads with the goal of completing the collection of the tenured generation before it becomes full. In normal operation, the CMS collector does most of its tracing and sweeping work with the application threads still running, so only brief pauses are seen by the application threads. However, if the CMS collector is unable to finish reclaiming the unreachable objects before the tenured generation fills up, or if an allocation cannot be satisfied with the available free space blocks in the tenured generation, then the application is paused and the collection is completed with all the application threads stopped. The inability to complete a collection concurrently is referred to as concurrent mode failure and indicates the need to adjust the CMS collector parameters. Concurrent mode failure typically triggers Full GC.
- 产生原因：CMS GC运行期间，老年代预留的空间不足以分配给新的对象。
- 触发GC类型：Full GC。
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