User threads (user-level threads) refers to the thread does not need kernel support implemented in the user program, which is independent of the operating system kernel, using the threads library provides application process creation, synchronization, thread scheduling and management functions to control user thread .
GC procedure CMS has six stages (four concurrent, two other suspended applications)
- First marker (STW initial mark)
- Concurrent mark (Concurrent marking)
- Concurrent interruptible precleaning (Concurrent precleaning)
- The final re-mark (STW remark)
- Cleanup concurrent (Concurrent sweeping)
- Concurrent reset (Concurrent reset)
initial mark, when re-sign, requires us to suspend other applications, then the two phases are not involved in user threads
