RFR 9: 8087286 Need a way to handle control-C and possibly some other signals

Chris Hegarty chris.hegarty at oracle.com
Tue Feb 2 16:58:30 UTC 2016


On 2 Feb 2016, at 16:35, Roger Riggs <Roger.Riggs at Oracle.com> wrote:

:

>>>>  - I agree with Peter, about the permission regarding the thread that executes
>>>>    the consumer. Does it make sense to support a ThreadFactory, or may that
>>>>    is overkill.
>>>> 
>>>> 
>>> Using InnocuousThread should be sufficient.
>>> 
>> Right, but then it should be specified.
> ok
>> 
>>> Adding a ThreadFactory to the register method would give more control but is probably more than necessary.
>>> 
>> Hmmm… maybe. But then it is very restrictive, unless there is some mechanism
>> to override it.
>> 
> same as current s.m.Signal implementation.

But, doesn’t s.m.Signal start a new thread from the VM created signal dispatcher thread
which has all permissions ( inherited ACC )?  j.u.Signal will be different, it would execute
the consumer with no permissions.

: 

>> So the use case is to register a handler and later restore the previously
>> set handler.  It is not possible for register to return the previously registered
>> handler, and then it is up the user to store it and reset it, as necessary. 
>> Rather than the default notion.
>> 
> Returning the previously set handler exposes a reference to some other subsystem's object.
> In some cases it might be a security risk. 

Right, but the user will have to have permission.

:

>>> if you have a Signal reference you have the power; similar to Process and ProcessHandle
>>> the security check is done to get the reference to begin with. From an auditing point of view,
>>> there is no ambiguity in code that has access to a Signal reference; if has the reference it can control
>>> the process.
>>> 
>> There is a potential issue when the Signal is delivered to the consumer when it
>> is raised, if, there is any thread, other than an innocuous thread, executing the
>> consumer.
>> 
>> Another small implementation question: is it still necessary for s.m.Signal.dispatch
>> to start a new Thread ?
>> 
> If it re-uses the VM's Signal Dispatch thread, the latency in the signal consumer might delay other signal
> handling.

I was not suggesting that it use the VM Signal Dispatch Thread. SignalImpl.dispatch,
the common dispatch path, already starts a new thread and executes s.m.dispatch.

>  Like with the Cleaner threads and functions, there is a concern about the impact of one of the clients
> on the shared resource (Thread). Starting a new thread allows the impact to be reduced.
> 
> There might be an argument for using the a common executor but it might also introduce additional
> latency in processing the signal depending on the state of the executor.
> Starting a new thread has more predictable behaviour.

I was actually suggesting supporting a variant taking a thread factory, since the
API will specify that the default handler thread, created per signal raised, will
execute with no permissions.

-Chris.

> Thanks, Roger
> 
>> 
>> -Chris.
>> 
>> 
>>> (I haven't done a review with the security folks on this yet).
>>> 
>>> Thanks, Roger
>>> 
>>> 
>>> 
>>>> -Chris.
>>>> 
>>>> On 1 Feb 2016, at 16:02, Roger Riggs 
>>>> 
>>>> <Roger.Riggs at oracle.com>
>>>> 
>>>>  wrote:
>>>> 
>>>> 
>>>> 
>>>>> Please review an API addition to handle signals such as SIGINT, SIGHUP, and SIGTERM.
>>>>> This JEP 260 motivated alternative to sun.misc.Signal supports the use case for
>>>>> interactive applications that need to handle Control-C and other signals.
>>>>> 
>>>>> The new java.util.Signal class provides a settable primary signal handler and a default
>>>>> signal handler.  The primary signal handler can be unregistered and handling is restored
>>>>> to the default signal handler.  System initialization registers default signal handlers
>>>>> to terminate on SIGINT, SIGHUP, and SIGTERM.  Use of the Signal API requires
>>>>> a permission if a SecurityManager is set.
>>>>> 
>>>>> The sun.misc.Signal implementation is modified to be layered on a common
>>>>> thread and dispatch mechanism. The VM handling of native signals is not affected.
>>>>> The command option to reduce signal use by the runtime with -Xrs is unmodified.
>>>>> 
>>>>> The changes to hotspot are minimal to rename the hardcoded callback to the Java
>>>>> Signal dispatcher.
>>>>> 
>>>>> Please review and comment on the API and implementation.
>>>>> 
>>>>> javadoc:
>>>>>  
>>>>> 
>>>>> http://cr.openjdk.java.net/~rriggs/signal-doc/
>>>>> 
>>>>> 
>>>>> 
>>>>> Webrev:
>>>>> jdk:  
>>>>> 
>>>>> http://cr.openjdk.java.net/~rriggs/webrev-signal-8087286/
>>>>> 
>>>>> 
>>>>> hotspot: 
>>>>> 
>>>>> http://cr.openjdk.java.net/~rriggs/webrev-hs-signal-8087286/
>>>>> 
>>>>> 
>>>>> 
>>>>> Issue:
>>>>>   
>>>>> 
>>>>> https://bugs.openjdk.java.net/browse/JDK-8087286
>>>>> 
>>>>> 
>>>>> 
>>>>> JEP 260:
>>>>>  
>>>>> 
>>>>> https://bugs.openjdk.java.net/browse/JDK-8132928
>>>>> 
>>>>> 
>>>>> 
>>>>> Thanks, Roger
>>>>> 
>>>>> 
>>>>> 
>>>>> 
> 




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