Using C# 4.0 features I want a generic wrapper for encapsulating functions and add a TimeOut parameter to them.
For example we have a function like:
T DoLengthyOperation()
Using Func we have:
Func<T>
This is good and call the function even Sync (Invloke) or Async(BeginInvoke).
Now think of a TimeOut to be added to this behavior and if DoLengthyOperation() returns in specified time we have true returned, otherwise false.
Something like:
FuncTimeOut<in T1, in T2, ..., out TResult, int timeOut, bool result>
Implement C# Generic Timeout
Don't return true/false for complete. Throw an exception.
I don't have time to implement it, but it should be possible and your basic signature would look like this:
T DoLengthyOperation<T>(int TimeoutInMilliseconds, Func<T> operation)
And you could call this method either by passing in the name of any Func<T> as an argument or define it place as a lambda expression. Unfortunately, you'll also need to provide an overload for different kind of function you want, as there's currently no way to specify a variable number a generic type arguments.
Instead of mixing out and bool I would instead construct a separate type to capture the return. For example
struct Result<T> {
private bool _isSuccess;
private T _value;
public bool IsSucces { get { return _success; } }
public T Value { get { return _value; } }
public Result(T value) {
_value = value;
_isSuccess = true;
}
}
This is definitely possible to write. The only problem is that in order to implement a timeout, it's necessary to do one of the following
Move the long running operation onto another thread.
Add cancellation support to the long running operation and signal cancellation from another thread.
Ingrain the notion of timeout into the operation itself and have it check for the time being expired at many points in the operation.
Which is best for you is hard to determine because we don't know enough about your scenario. My instinct though would be to go for #2 or #3. Having the primary code not have to switch threads is likely the least impactful change to your code.
Related
I've been searching for a function that takes an object of type Lock
and runs a block of code with that lock taking care of locking and also unlocking.
I'd implement it as follows:
fun <T : Lock> T.runLocked(block: () -> Unit) {
lock()
try {
block()
} finally {
unlock()
}
}
Used like this:
val l = ReentrantLock()
l.runLocked {
println(l.isLocked)
}
println(l.isLocked)
//true
//false
Anything available like this? I could only find the synchronized function which cannot be used like this.
You are looking for withLock, which has the exact implementation you've written yourself, except it has a generic parameter for the result of the block instead of the receiver type.
You can find other concurrency related methods of the standard library here, in the kotlin.concurrent package.
I'm trying to write my own boolean "abstract" with some additional functions.
#forward
abstract MyBool(Bool) {
public inline function new(b:Bool) {
this = b;
}
#:from
public static inline function fromBool(b:Bool):MyBool {
return new MyBool(b);
}
#:to
public inline function toBool():Bool {
return this;
}
// some additional functions
}
In principal this works fine:
var t:T = true;
if(t) {
trace("1");
}
t.someStrangeMethod();
However #:forward does not forward basic boolean-operators like "!":
var f:T = false;
if(!f) { // fails here, because "!" is not defined as an operator for MyBool ...
trace("2");
}
The error message is "MyBool should be Bool", which I find quite strange because MyBool is an abstract of a Bool with #:forward annotation and there is a #:to-method.
Of course there are some easy workarounds. One could either use:
if(!f.toBool()) {
trace("2");
}
and/or add a function annotated with #:op(!A) to the abstract:
#:op(!A)
public inline function notOp():Bool {
return !this;
}
However I do not like both methods:
I dislike adding #:op(...) to MyBool, because creating a method for each possible operator would require much code (Maybe not with a boolean, but e.g. with an Int, Float, ...).
I dislike using !var.toBool(). If someone has already written quite some code (s)he does not want to go through all of it, when (s)he simply wants to change Bool to a MyBool ... I mean of course (s)he could also cast Bool to MyBool whenever adding new code, but that can be horrible too.
So I was wondering if anyone has a better idea? Is there maybe another "#:forward"-like compiling metadata, I do not know about yet?
There's an open feature request regarding this:
Can #:forward also forward underlying operator overloads? (#5035)
One way to make your code example work is to allow implicit conversions with to Bool. I'm not entirely sure why the equivalent #:to function doesn't work here, as the Haxe Manual states that "Class field casts have the same semantics".
abstract MyBool(Bool) to Bool {
Apart from that, I think the only options is to declare an #:op function for each operator you want to support. If declared without a body, the underlying type's operator will be forwarded:
#:op(!A) function notOp():MyBool;
If your main goal is to just add methods to the Bool type, then perhaps avoid the problem altogether by instead creating a class that adds methods to Bool via static extension (documented in the Haxe manual). This method would eliminate the need for operator forwarding.
For a parameter class
class Criteria {
private Map params;
public getMap(){ return params; }
}
and a service method accept this criteria
class Service{
public List<Person> query(Criteria criteria){ ... }
}
A custom featureMatcher is used to match the criteria key
private Matcher<Criteria> hasCriteria(final String key, final Matcher<?> valueMatcher){
return new FeatureMatcher<Criteria, Object>((Matcher<? super Object>)valueMatcher, key, key){
#Override protected Object featureValueOf(Criteria actual){
return actual.getMap().get(key);
}
}
}
when using mockito to veryify the arguments:
verify(Service).query((Criteria) argThat("id", hasCriteria("id", equalTo(new Long(12)))));
The error message shows that:
Argument(s) are different! Wanted:
Service.query(
id <12L>
);
-> at app.TestTarget.test_id (TestTarget.java:134)
Actual invocation has different arguments:
Service.query(
app.Criteria#509f5011
);
If I use ArugmentCaptor,
ArgumentCaptor<Criteria> argument = ArgumentCaptor.forClass(Criteria.class);
verify(Service).query(argument.capture());
assertThat(argument.getValue(), hasCriteria("id", equalTo(new Long(12))));
The message is much better:
Expected: id <12L> but id was <2L>
How can I get such message, without using ArgumentCaptor?
The short answer is to adjust the Criteria code, if it's under your control, to write a better toString method. Otherwise, you may be better off using the ArgumentCaptor method.
Why is it hard to do without ArgumentCaptor? You know you're expecting one call, but Mockito was designed to handle it even if you have a dozen similar calls to evaluate. Even though you're using the same matcher implementation, with the same helpful describeMismatch implementation, assertThat inherently tries once to match where verify sees a mismatch and keeps trying to match any other call.
Consider this:
// in code:
dependency.call(true, false);
dependency.call(false, true);
dependency.call(false, false);
// in test:
verify(mockDependency).call(
argThat(is(equalTo(true))),
argThat(is(equalTo(true))));
Here, Mockito wouldn't know which of the calls was supposed to be call(true, true); any of the three might have been it. Instead, it only knows that there was a verification you were expecting that was never satisfied, and that one of three related calls might have been close. In your code with ArgumentCaptor, you can use your knowledge that there's only one call, and provide a more-sane error message; for Mockito, the best it can do is to output all the calls it DID receive, and without a helpful toString output for your Criteria, that's not very helpful at all.
I used the below to see how dart calls methods passed in to other methods to see what context the passed in method would/can be called under.
void main() {
var one = new IDable(1);
var two = new IDable(2);
print('one ${caller(one.getMyId)}'); //one 1
print('two ${caller(two.getMyId)}'); //two 2
print('one ${callerJustForThree(one.getMyId)}'); //NoSuchMethod Exception
}
class IDable{
int id;
IDable(this.id);
int getMyId(){
return id;
}
}
caller(fn){
return fn();
}
callerJustForThree(fn){
var three = new IDable(3);
three.fn();
}
So how does caller manager to call its argument fn without a context i.e. one.fn(), and why does callerJustForThree fail to call a passed in fn on an object which has that function defined for it?
In Dart there is a difference between an instance-method, declared as part of a class, and other functions (like closures and static functions).
Instance methods are the only ones (except for constructors) that can access this. Conceptually they are part of the class description and not the object. That is, when you do a method call o.foo() Dart first extracts the class-type of o. Then it searches for foo in the class description (recursively going through the super classes, if necessary). Finally it applies the found method with this set to o.
In addition to being able to invoke methods on objects (o.foo()) it is also possible to get a bound closure: o.foo (without the parenthesis for the invocation). However, and this is crucial, this form is just syntactic sugar for (<args>) => o.foo(<args>). That is, this just creates a fresh closure that captures o and redirects calls to it to the instance method.
This whole setup has several important consequences:
You can tear off instance methods and get a bound closure. The result of o.foo is automatically bound to o. No need to bind it yourself (but also no way to bind it to a different instance). This is way, in your example, one.getMyId works. You are actually getting the following closure: () => one.getMyId() instead.
It is not possible to add or remove methods to objects. You would need to change the class description and this is something that is (intentionally) not supported.
var f = o.foo; implies that you get a fresh closure all the time. This means that you cannot use this bound closure as a key in a hashtable. For example, register(o.foo) followed by unregister(o.foo) will most likely not work, because each o.foo will be different. You can easily see this by trying print(o.foo == o.foo).
You cannot transfer methods from one object to another. However you try to access instance methods, they will always be bound.
Looking at your examples:
print('one ${caller(one.getMyId)}'); //one 1
print('two ${caller(two.getMyId)}'); //two 2
print('one ${callerJustForThree(one.getMyId)}'); //NoSuchMethod Exception
These lines are equivalent to:
print('one ${caller(() => one.getMyId())}');
print('two ${caller(() => two.getMyId())}');
print('one ${callerJustForThree(() => one.getMyId())}';
Inside callerJustForThree:
callerJustForThree(fn){
var three = new IDable(3);
three.fn();
}
The given argument fn is completely ignored. When doing three.fn() in the last line Dart will find the class description of three (which is IDable) and then search for fn in it. Since it doesn't find one it will call the noSuchMethod fallback. The fn argument is ignored.
If you want to call an instance member depending on some argument you could rewrite the last example as follows:
main() {
...
callerJustForThree((o) => o.getMyId());
}
callerJustForThree(invokeIDableMember){
var three = new IDable(3);
invokeIDableMember(three);
}
I'll try to explain, which is not necessarily a strength of mine. If something I wrote isn't understandable, feel free to give me a shout.
Think of methods as normal objects, like every other variable, too.
When you call caller(one.getMyId), you aren't really passing a reference to the method of the class definition - you pass the method "object" specific for instance one.
In callerJustForThree, you pass the same method "object" of instance one. But you don't call it. Instead of calling the object fn in the scope if your method, you are calling the object fn of the instance three, which doesn't exist, because you didn't define it in the class.
Consider this code, using normal variables:
void main() {
var one = new IDable(1);
var two = new IDable(2);
caller(one.id);
caller(two.id);
callerJustForThree(one.id);
}
class IDable{
int id;
IDable(this.id);
}
caller(param){
print(param);
}
callerJustForThree(param){
var three = new IDable(3);
print(three.id); // This works
print(param); // This works, too
print(three.param); // But why should this work?
}
It's exactly the same concept. Think of your callbacks as normal variables, and everything makes sense. At least I hope so, if I explained it good enough.
UPDATE
I have to apologize for confusing the readers. After I got totally lost in the code, I reverted all my changes from Mercurial repo, carefully applied the same logic as before -- and it worked. The answers below helped me understand the (new to me) concept better, and for that I gave them upvotes.
Bottom line: if a call to a missing method happens within a closure, and resolution set to DELEGATE_FIRST, methodMissing() will be called on the delegate. If it doesn't -- check you own code, there is a typo somewhere.
Thanks a lot!
Edit:
OK, now that you've clarified what your are doing (somewhat ;--))
Another approach (one that I use for DSLs) is to parse your closure group to map via a ClosureToMap utility like this:
// converts given closure to map method => value pairs (1-d, if you need nested, ask)
class ClosureToMap {
Map map = [:]
ClosureToMap(Closure c) {
c.delegate = this
c.resolveStrategy = Closure.DELEGATE_FIRST
c.each{"$it"()}
}
def methodMissing(String name, args) {
if(!args.size()) return
map[name] = args[0]
}
def propertyMissing(String name) { name }
}
// Pass your closure to the utility and access the generated map
Map map = new ClosureToMap(your-closure-here)?.map
Now you can iterate through the map, perhaps adding methods to applicable MCL instance. For example, some of my domains have dynamic finders like:
def finders = {
userStatusPaid = { Boolean active = true->
eq {
active "$active"
paid true
}
}
}
I create a map using the ClosureToMap utility, and then iterate through, adding map keys (methods, like "userStatus") and values (in this case, closure "eq") to domain instance MCL, delegating the closure to our ORM, like so:
def injectFinders(Object instance) {
if(instance.hasProperty('finders')) {
Map m = ClosureToMap.new(instance.finders).map
m?.each{ String method, Closure cl->
cl.delegate = instance.orm
cl.resolveStrategy = Closure.DELEGATE_FIRST
instance.orm.metaClass."$method" = cl
}
}
}
In this way in controller scope I can do, say:
def actives = Orders.userStatusPaid()
and "eq" closure will delegate to the ORM and not domain Orders where an MME would occur.
Play around with it, hopefully I've given you some ideas for how to solve the problem. In Groovy, if you can't do it one way, try another ;--)
Good luck!
Original:
Your missingMethod is defined on string metaclass; in order for it to be invoked, you need "someString".foo()
If you simply call foo() by itself within your closure it will fail, regardless of delegation strategy used; i.e. if you don't use the (String) delegate, good luck. Case in point, do "".foo() and it works.
I don't fully understand the issue either, why will you not have access to the closure's delegate? You are setting the closure's delegate and will invoke the closure, which means you will have access to the delegate within the closure itself (and can just delegate.foo())
nope, you will not catch a missing method and redirect it to the delegate with metaclass magic.
the closure delegate is the chance to capture those calls and adapt them to the backing domain.
that means...
you should create your own delegate with the methods required by the dsl.
do not try to force a class to do delegate work if it's not designed for the task, or the code will get really messy in not time.
keep everything dsl related in a set of specially designed delegate classes and everything will suddenly become ridiculously simple and clear.