[GitHub] [rocketmq] medusar commented on issue #2306: get Selector don't need to judge by programming

[GitBox <gi...@apache.org>]

medusar commented on issue #2306:
URL: https://github.com/apache/rocketmq/issues/2306#issuecomment-699747793


   Yes, the default `SelectorProvider` will choose the right `Selector` based on the system,  as for Linux, it will use `EPollSelectorProvider` if the kernel is 2.6 or newer otherwise it will choose `PollSelectorProvider`.
   But as the the JDK api says, users can specify their own SelectorProvider: 
   ```
   The first invocation of this method locates the default provider object as follows:
   
   If the system property java.nio.channels.spi.SelectorProvider is defined then it is taken to be the fully-qualified name of a concrete provider class. The class is loaded and instantiated; if this process fails then an unspecified error is thrown.
   
   If a provider class has been installed in a jar file that is visible to the system class loader, and that jar file contains a provider-configuration file named java.nio.channels.spi.SelectorProvider in the resource directory META-INF/services, then the first class name specified in that file is taken. The class is loaded and instantiated; if this process fails then an unspecified error is thrown.
   
   Finally, if no provider has been specified by any of the above means then the system-default provider class is instantiated and the result is returned.
   
   Subsequent invocations of this method return the provider that was returned by the first invocation.
   ```
   So, IMHO, if it is the purpose of RocketMQ to disable user-specified Selector and use `EPollSelectorProvider` regardless of user configuration, use only `Selector.open()` would not work.


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