On 2 June 2013 at 6:48:13 AM, revin ([email protected]) wrote:
OK,thanks guys,
what I've posted is trying to simplify the question,
this is the real problem:
Yes indeed, try{...} frame "is" work on the "execution flow (stack trace)",
but that's C, that's C++, that's java!
They're all sync language!
When it comes to nodeJs, shouldn't it be async as well as nodeJs itself?
Let's see a real project:
modules:
httpd.js main module, setup server, dispatch requests.
httpdoc.js helper module, if request is a file (e.g.: /index.htm), the request
will be directed from httpd.js to this module
... other modules
REQUEST => httpd.js =(ANALYSE,DISPATCH)=> httpdoc.js
we should handler all errors inside httpd.js:
file not found: respond 404
access denied: respond 404
file IO failure: respond 500
internal error: respond 500
other responds...
then in httpdocs.js:
fs.ReadStream("...").on("error",function(e){
throw e;
});
The real question is "Why throw?"
If you read "throw" as "unwind the stack and handle errors at a higher call
site", and know that async code has already unwound the stack and started
something anew, throw doesn't look like the right tool. It's just a tool --
there are other approaches.
How about calling an error handler on something defined in your httpd.js?
That's a simple approach -- make all of those sub-handlers pass their errors on.
Another, more robust approach that's been baked into node core more recently is
to use error domains: If you set all of your EventEmitter's domain property to
a domain, the domain's error handler will fire for all errors in that domain.
Still fully async.
[snip]
But since nodeJs follows the definition of try{...} after some sync languages,
rather than to start a new one for async languages like nodeJs itself,
these code won't run like expected.
Indeed: node is just javascript -- it has not extended the language at all, so
the concepts are the same. try/catch is synchronous, still only concerned with
the regular execution stack.
Could any one come up with a solution?
How to catch exceptions on event callbacks?
Please don't say that you can setup an uncaught exception handler,
there can be only one of it,
And that's where you're wrong: error domains give you an uncaught exception
handler for each separate domain.
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