why jmeter not stop thread at Duraion time - jmeter

Question

In my test plan, I create a Thread Group configured as below:
1. Action to be taken after a Sampler error: Continue
2. Number of Threads(users):10000
3. Ramp-up Period(in seconds):1
4. Loop Count:1
5. Duration(seconds):2
6. Startup delay(seconds):10
There is an Http Request Sampler in Thread Group.
After run the test plan, in jmeter.log
2019-04-30 15:46:01,558 INFO o.a.j.e.StandardJMeterEngine: Starting ThreadGroup: 1 : Thread Group-WB
2019-04-30 15:46:01,558 INFO o.a.j.e.StandardJMeterEngine: Starting 10000 threads for group Thread Group-WB.
2019-04-30 15:46:01,558 INFO o.a.j.e.StandardJMeterEngine: Thread will continue on error
2019-04-30 15:46:01,559 INFO o.a.j.t.ThreadGroup: Starting thread group... number=1 threads=10000 ramp-up=1 delayedStart=false
2019-04-30 15:46:06,549 INFO o.a.j.t.ThreadGroup: Started thread group number 1
2019-04-30 15:46:06,549 INFO o.a.j.e.StandardJMeterEngine: All thread groups have been started
2019-04-30 15:46:11,559 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-1
2019-04-30 15:46:11,562 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-2
2019-04-30 15:46:11,614 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-67
...
2019-04-30 15:46:15,541 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-5884
2019-04-30 15:46:15,541 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-5890
2019-04-30 15:46:15,541 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-5891
...
2019-04-30 15:46:15,367 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-7239
...
2019-04-30 15:46:21,913 INFO o.a.j.t.JMeterThread: Thread is done: Thread Group-WB 1-8506
2019-04-30 15:46:21,912 INFO o.a.j.t.JMeterThread: Thread finished: Thread Group-WB 1-8505
...
2019-04-30 15:46:16,872 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-8042
2019-04-30 15:46:16,872 INFO o.a.j.t.JMeterThread: Thread started: Thread Group-WB 1-8041
2019-04-30 15:46:18,767 INFO o.a.j.t.JMeterThread: Stopping because end time detected by thread: Thread Group-WB 1-7239
2019-04-30 15:46:18,767 INFO o.a.j.t.JMeterThread: Thread is done: Thread Group-WB 1-7239
2019-04-30 15:46:18,767 INFO o.a.j.t.JMeterThread: Thread finished: Thread Group-WB 1-7239
...
2019-04-30 15:47:35,716 INFO o.a.j.t.JMeterThread: Thread is done: Thread Group-WB 1-9783
2019-04-30 15:47:35,716 INFO o.a.j.t.JMeterThread: Thread finished: Thread Group-WB 1-9783
2019-04-30 15:47:36,941 INFO o.a.j.t.JMeterThread: Stopping because end time detected by thread: Thread Group-WB 1-1037
2019-04-30 15:47:36,942 INFO o.a.j.t.JMeterThread: Thread is done: Thread Group-WB 1-1037
2019-04-30 15:47:36,942 INFO o.a.j.t.JMeterThread: Thread finished: Thread Group-WB 1-1037
2019-04-30 15:47:36,944 INFO o.a.j.e.StandardJMeterEngine: Notifying test listeners of end of test
2019-04-30 15:47:36,945 INFO o.a.j.g.u.JMeterMenuBar: setRunning(false, *local*)
The first Thread Group-wisebuy 1-1 start at 2019-04-30 15:46:11,559
I set Ramp-up Period as 1 second,why Thread Group-wisebuy 1-5891 started at 2019-04-30 15:46:15,541 ?
I set Duration as 2 seconds,why Thread Group-wisebuy 1-7239 stopping at 2019-04-30 15:46:18,767 ?

Answer 1

From the JMeter User's Manual:
The ramp-up period tells JMeter how long to take to "ramp-up" to the full number of threads chosen. If 10 threads are used, and the ramp-up period is 100 seconds, then JMeter will take 100 seconds to get all 10 threads up and running. Each thread will start 10 (100/10) seconds after the previous thread was begun.
By setting the ramp-up period to just 1 second, you're basically telling JMeter to start all 10,000 threads at once (i.e., as fast as it can).
Hence Thread 1-5891 started very soon after the first one. It looks like Thread 1-7239 started about 16s in, and therefore ended at around 18s because the duration = 2 seconds.
If you meant to start 1 user per second then you can set the ramp-up period = 1 second per # of users (10,000 seconds).