RFR: 8260366: ExtendedSocketOptions <clinit> can deadlock in some circumstances [v4]

[Daniel Fuchs]

On Thu, 18 Feb 2021 13:31:07 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>> Hi Jaikiran,
>> 
>> I tested with my suggested change and i did not see any deadlock at my local Linux environment. I just ran  test in loop and it worked as expected.
>> 
>> Thanks,
>> Vyom
>
> Hello Vyom,
> 
> The trick is to change the test case to have something like this in the "task":
> 
> diff --git a/test/jdk/sun/net/ext/ExtendedSocketOptionsTest.java b/test/jdk/sun/net/ext/ExtendedSocketOptionsTest.java
> index 0702abf5279..26c8a1384a2 100644
> --- a/test/jdk/sun/net/ext/ExtendedSocketOptionsTest.java
> +++ b/test/jdk/sun/net/ext/ExtendedSocketOptionsTest.java
> @@ -96,7 +96,11 @@ public class ExtendedSocketOptionsTest {
>                  classLoadingTriggerLatch.countDown();
>                  // wait for the other task to let us know it's ready too, to load the class
>                  classLoadingTriggerLatch.await();
> -                return Class.forName(this.className);
> +                final Class<?> c = Class.forName(this.className);
> +                // let's call getInstance on sun.net.ext.ExtendedSocketOptions
> +                final Class<?> k = Class.forName("sun.net.ext.ExtendedSocketOptions");
> +                final Object extSocketOptions = k.getDeclaredMethod("getInstance").invoke(null);
> +                return c;
>              } catch (Exception e) {
>                  System.err.println("Failed to load " + this.className);
>                  throw new RuntimeException(e);
> 
> Essentially, trigger a call to `sun.net.ext.ExtendedSocketOptions#getInstance` and a classload of `jdk.net.ExtendedSocketOptions` simultaneously from different threads. That will end up with:
> 
> 
> 
> "pool-1-thread-1" #16 prio=5 os_prio=31 cpu=18.25ms elapsed=120.03s tid=0x00007ff9008c8a00 nid=0x6203 waiting for monitor entry  [0x0000700010c8b000]
>    java.lang.Thread.State: BLOCKED (on object monitor)
> 	at sun.net.ext.ExtendedSocketOptions.register(java.base at 17-internal/ExtendedSocketOptions.java:197)
> 	- waiting to lock <0x000000070f9f8e68> (a java.lang.Class for sun.net.ext.ExtendedSocketOptions)
> 	at jdk.net.ExtendedSocketOptions.<clinit>(jdk.net at 17-internal/ExtendedSocketOptions.java:234)
> 	at java.lang.Class.forName0(java.base at 17-internal/Native Method)
> 	at java.lang.Class.forName(java.base at 17-internal/Class.java:375)
> 	at ExtendedSocketOptionsTest$Task.call(ExtendedSocketOptionsTest.java:100)
> 	at ExtendedSocketOptionsTest$Task.call(ExtendedSocketOptionsTest.java:84)
> 	at java.util.concurrent.FutureTask.run(java.base at 17-internal/FutureTask.java:264)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base at 17-internal/ThreadPoolExecutor.java:1135)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base at 17-internal/ThreadPoolExecutor.java:635)
> 	at java.lang.Thread.run(java.base at 17-internal/Thread.java:831)
> 
> "pool-1-thread-2" #17 prio=5 os_prio=31 cpu=8.76ms elapsed=120.03s tid=0x00007ff90102be00 nid=0x6403 in Object.wait()  [0x0000700010d8e000]
>    java.lang.Thread.State: RUNNABLE
> 	at java.lang.Class.forName0(java.base at 17-internal/Native Method)
> 	- waiting on the Class initialization monitor for jdk.net.ExtendedSocketOptions
> 	at java.lang.Class.forName(java.base at 17-internal/Class.java:375)
> 	at sun.net.ext.ExtendedSocketOptions.getInstance(java.base at 17-internal/ExtendedSocketOptions.java:185)
> 	- locked <0x000000070f9f8e68> (a java.lang.Class for sun.net.ext.ExtendedSocketOptions)
> 	at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(java.base at 17-internal/Native Method)
> 	at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(java.base at 17-internal/NativeMethodAccessorImpl.java:78)
> 	at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(java.base at 17-internal/DelegatingMethodAccessorImpl.java:43)
> 	at java.lang.reflect.Method.invoke(java.base at 17-internal/Method.java:566)
> 	at ExtendedSocketOptionsTest$Task.call(ExtendedSocketOptionsTest.java:102)
> 	at ExtendedSocketOptionsTest$Task.call(ExtendedSocketOptionsTest.java:84)
> 	at java.util.concurrent.FutureTask.run(java.base at 17-internal/FutureTask.java:264)
> 	at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base at 17-internal/ThreadPoolExecutor.java:1135)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base at 17-internal/ThreadPoolExecutor.java:635)
> 	at java.lang.Thread.run(java.base at 17-internal/Thread.java:831)

> Hello Daniel, I had thought about it in my previous commit. But this won't work, since in the normal case where the `ClassNotFoundException` doesn't get thrown, the `instance` is actually set in the `register` method which gets triggered due to the class load on `jdk.net.ExtendedSocketOptions`. As a result, returning the local `ext` variable won't work in that case, unless of course I do `ext = instance` in both the catch block and outside of it, which would, IMO, defeat the purpose of optimization in that last commit.

Oh - right - still - if you'd stick with that fix - I believe you should do that:

            try {
                // If the class is present, it will be initialized which
                // triggers registration of the extended socket options.
                Class<?> c = Class.forName("jdk.net.ExtendedSocketOptions");
                ext = instance;
            } catch (ClassNotFoundException e) {
                // the jdk.net module is not present => no extended socket options
                ext = instance = new NoExtendedSocketOptions();
            }
        }
        return ext;
 ```
 
 Anyway: waiting for the next fix :-)

-------------

PR: https://git.openjdk.java.net/jdk/pull/2601