How does tomcat serve multiple requests with same thread simulatenouly?

Question

As per the various documentation available online eg this, I understand that with NIO mode maxConnections are not dependent on maxThreads parameter and each thread can serve any number of connections.

If I take a thread-dump, I get to see what all my threads are doing. Each of these threads is handling one request and this trace remains the same for long-running requests between multiple dumps taken in a quick interval, so how can these threads serve multiple request at the same time. I am using Tomcat v8.0.23, with Java v8.0.45.

"http-nio-8080-exec-35" #151 daemon prio=5 os_prio=0 tid=0x00007f5e70021000 nid=0x7337 runnable [0x00007f5f4ebe8000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.read(SocketInputStream.java:150)
        at java.net.SocketInputStream.read(SocketInputStream.java:121)
        at java.io.BufferedInputStream.fill(BufferedInputStream.java:246)
        at java.io.BufferedInputStream.read1(BufferedInputStream.java:286)
        at java.io.BufferedInputStream.read(BufferedInputStream.java:345)
        - locked <0x000000061d4a4070> (a java.io.BufferedInputStream)
        at org.apache.thrift.transport.TIOStreamTransport.read(TIOStreamTransport.java:127)

It doesn't, and there is no NIO here. – user207421 Sep 12 '19 at 23:55 — user207421, Sep 12 '19 at 23:55

score 2 · Accepted Answer · answered Sep 12 '19 at 20:45

You have misunderstood.

Assuming we are only considering the synchronous, blocking Servlet API then Tomcat will support maxConnections but only maxThreads of those can be allocated to a processing thread at any one time.

The idea is that the majority of the connections will be essentially idle in HTTP keep-alive between requests. Hence a single Poller thread monitors these idle connections and passes them to a processing thread when there is data to process.

In earlier Tomcat releases, the BIO connector allocated 1 thread to a connection so that thread was in use even if the connection was idle which was inefficient.

How does tomcat serve multiple requests with same thread simulatenouly?

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