Feature/quic httpreq init #2
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jrhee17
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Nov 1, 2021
…tor (netty#10890) Motivation: A race detector discovered a data race in GlobalEventExecutor present in netty 4.1.51.Final: ``` Write of size 4 at 0x0000cea08774 by thread T103: #0 io.netty.util.internal.DefaultPriorityQueue.poll()Lio/netty/util/internal/PriorityQueueNode; DefaultPriorityQueue.java:113 #1 io.netty.util.internal.DefaultPriorityQueue.poll()Ljava/lang/Object; DefaultPriorityQueue.java:31 #2 java.util.AbstractQueue.remove()Ljava/lang/Object; AbstractQueue.java:113 #3 io.netty.util.concurrent.AbstractScheduledEventExecutor.pollScheduledTask(J)Ljava/lang/Runnable; AbstractScheduledEventExecutor.java:133 #4 io.netty.util.concurrent.GlobalEventExecutor.fetchFromScheduledTaskQueue()V GlobalEventExecutor.java:119 netty#5 io.netty.util.concurrent.GlobalEventExecutor.takeTask()Ljava/lang/Runnable; GlobalEventExecutor.java:106 netty#6 io.netty.util.concurrent.GlobalEventExecutor$TaskRunner.run()V GlobalEventExecutor.java:240 netty#7 io.netty.util.internal.ThreadExecutorMap$2.run()V ThreadExecutorMap.java:74 netty#8 io.netty.util.concurrent.FastThreadLocalRunnable.run()V FastThreadLocalRunnable.java:30 netty#9 java.lang.Thread.run()V Thread.java:835 netty#10 (Generated Stub) <null> Previous read of size 4 at 0x0000cea08774 by thread T110: #0 io.netty.util.internal.DefaultPriorityQueue.size()I DefaultPriorityQueue.java:46 #1 io.netty.util.concurrent.GlobalEventExecutor$TaskRunner.run()V GlobalEventExecutor.java:263 #2 io.netty.util.internal.ThreadExecutorMap$2.run()V ThreadExecutorMap.java:74 #3 io.netty.util.concurrent.FastThreadLocalRunnable.run()V FastThreadLocalRunnable.java:30 #4 java.lang.Thread.run()V Thread.java:835 netty#5 (Generated Stub) <null> ``` The race is legit, but benign. To trigger it requires a TaskRunner to begin exiting and set 'started' to false, more work to be scheduled which starts a new TaskRunner, that work then needs to schedule additional work which modifies 'scheduledTaskQueue', and then the original TaskRunner checks 'scheduledTaskQueue'. But there is no danger to this race as it can only produce a false negative in the condition which causes the code to CAS 'started' which is thread-safe. Modifications: Delete problematic references to scheduledTaskQueue. The only way scheduledTaskQueue could be modified since the last check is if another TaskRunner is running, in which case the current TaskRunner doesn't care. Result: Data-race free code, and a bit less code to boot.
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