ARM API Support

Joe Darcy joe.darcy at
Thu Jun 24 07:57:39 PDT 2010

Rémi Forax wrote:
> Le 24/06/2010 02:08, Joe Darcy a écrit :
>> Greetings
>> The initial API changes to support the Project Coin feature automatic
>> resource management (ARM) blocks have been pushed into JDK 7 [1] and
>> will appear in subsequent builds. The corresponding compiler changes to
>> support the actual language feature remain in progress.
>> The initial API work to support ARM was divided into two pieces,
>> essential API support and retrofitting platform classes. The essential
>> support includes:
>> * A new interface java.lang.AutoCloseable which defines a single method
>>    void close() throws Exception
>> * A new enum constant in the language model:
>>    javax.lang.model.element.ElementKind.RESOURCE_VARIABLE
>> * Methods on java.lang.Throwable to add and retrieve information about
>> suppressed exceptions, including printing out suppressed exceptions in
>> stack traces.
>> The retrofitting includes:
>> * Having extend java.lang.AutoCloseable. (From a
>> typing perspective, a subtype of AutoCloseable can be declared to throw
>> fewer exceptions than the supertype. Therefore is is fine for the close
>> method in AutoCloseable to throw Exception and the close method in
>> Closeable to throw the more specific IOException. It would even be fine
>> for the close method in a subtype of AutoCloseable to be declared to
>> throw no exceptions at all.)
>> * Adding a close method to java.nio.channels.FileLock and having
>> FileLock implement AutoCloseable.
>> * Adding Closeable as an interface implemented by
>> Other platform classes may be retrofitted to implement AutoCloseable or
>> Closable in future builds.
>> Compared to the API support in earlier versions of the ARM proposal, the
>> top-level interface to mark participation in ARM is in package java.lang
>> rather than its own package and, after consultation with the JDBC and
>> graphics teams, neither java.sql.* nor java.awt.Graphics were
>> retrofitted for ARM.
>> -Joe
>> [1]
> There is a bug in printStackTrace(PrintStreamOrWriter)
> Set<Throwable> dejaVu = new HashSet<Throwable>();
> should be:
> Set<Throwable> dejaVu = Collections.newSetFromMap(
> new IdentityHashMap<Throwable,Boolean>());
> The current code doesn't work as expected if an exception overrides 
> Throwable.equals.

Hi Rémi,

Thanks for catching this bug.  I'll correct that when I next edit the 
file -- I plan to change the addSuppressedException method to throw an 
exception if the exception tries to suppress itself.


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