[8] Review Request for 8007292 : Add JavaFX internal packages to package.access

[Joseph Darcy]

On 10/9/2013 6:18 PM, David Holmes wrote:
> cc'ing Joe Darcy. :)
>
> Joe: there is a try-with-resources question for you below ...
>
> On 9/10/2013 11:20 PM, Sean Mullan wrote:
>> On 10/09/2013 05:14 AM, Erik Joelsson wrote:
>>> On 2013-10-09 06:33, David Holmes wrote:
>>>> In the tool this code doesn't show correct use of try-with-resources:
>>>>
>>>> 51         try (BufferedReader br = new BufferedReader(new
>>>> FileReader(args[0]));
>>>>   52              BufferedWriter bw = new BufferedWriter(new
>>>> FileWriter(args[1]))) {
>>>>
>>>> The FileReader and FileWriter should also be covered by TWR:
>>>>
>>>>   try (FileReader fr = new FileReader(args[0]);
>>>>        BufferedReader br = new BufferedReader(fr);
>>>>        FileWriter fw = new FileWriter(args[1]);
>>>>        BufferedWriter bw = new BufferedWriter(fw)) {
>>>>
>>> I'm not familiar with the try-with-resources, but calling close on a
>>> BufferedReader/writer will close the underlying reader/writer so 
>>> nothing
>>> will be left open, will it not?
>>
>> That's what I thought as well. David?
>
> It maybe that I am overly pedantic with this but the issue is that 
> with the original code if the BufferedReader/Writer constructors throw 
> an exception then the FileReader/Writer that was already created would 
> not be closed. The revised code accounts for this.
>
> Joe: what is best-practice here? I see a lot of examples of t-w-r 
> where there is a set of chained I/O streams and only the outermost one 
> is a t-w-r resource. And that seems wrong to me.

It is a hazard (I thought I had published a blog entry on this very 
tropic, but apparently not). The most robust pattern is

try(OriginalResource r1 = new OriginalResource;
     WrappingResource r2 = new WrappingResource(r1);
     AnnotherWrappingResource r3 = new WrappingResource(r2)) { ...}

One thing to watch out for in this pattern is a non-idempotent close. 
Calling close on r3 will presumably propagate a close call to r2, and 
then r2 to r1. So give the desguaring the try-with-resource and the 
expected behavior of the wrapping in a normal termination situation, 
close on r3 gets called once, close on r2 gets called twice (first from 
the close on r3, second close from try-with-resources), and close on r1 
gets called three times.

HTH,

-Joe