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clojurians | clojure | it lets you keep the logic you wanted without having all the race conditions (as long as you use it properly) | 2017-11-21T17:35:35.000189 | Margaret |
clojurians | clojure | Oh, you're saying compare-and-set! should be used not only for the implementation of compareAndSet, but also for the other implementations too? | 2017-11-21T17:37:05.000114 | Earlie |
clojurians | clojure | right - it lets you coordinate in a more flexible way than swap! | 2017-11-21T17:37:51.000035 | Margaret |
clojurians | clojure | I apologize for not reading that more carefully. Makes sense. :slightly_smiling_face: | 2017-11-21T17:38:08.000298 | Earlie |
clojurians | clojure | I didn't even know `compare-and-set!` was a thing until I went to implement IAtom. | 2017-11-21T17:38:28.000013 | Earlie |
clojurians | clojure | <@Margaret> Like this?
```
(defn- project-g-counter [p]
(reduce + (vals p)))
;; (defn- swap-g-counter [p n f & args]
;; (let [oldv (project-g-counter p)
;; newv (apply f oldv args)]
;; (assert (number? newv) "Swap! G-Counter function must return a Number")
;; (assert (>= newv oldv) "G-Counter is grow only")
;; (update p n + (- newv oldv))))
(defn- swap-g-counter [this f & args]
(let [p (.p this)
n (.n this)]
(loop []
(let [oldval @this
newval (apply f oldval args)
pval @p
nval (update pval n + (- newval oldval))]
(if (compare-and-set! p pval nval)
newval
(recur))))))
(deftype G-Counter [p n]
clojure.lang.IDeref
(deref [this]
(reduce + (vals p))
;; (project-g-counter @p)
)
clojure.lang.IAtom
(swap [this f]
(swap-g-counter this f)
;; (project-g-counter (swap! p swap-g-counter n f))
)
(swap [this f a]
(swap-g-counter this f a)
;; (project-g-counter (swap! p swap-g-counter n f a))
)
(swap [this f a b]
(swap-g-counter this f a b)
;; (project-g-counter (swap! p swap-g-counter n f a b))
)
(swap [this f a b args]
(apply swap-g-counter this f a b args)
;; (project-g-counter (apply swap! p swap-g-counter n f a b args))
)
(compareAndSet [this oldv newv]
(loop []
(let [pval @p]
(if (not= oldv (project-g-counter pval))
false
(or (compare-and-set! p pval (swap-g-counter pval n + (- newv oldv)))
(recur))))))
(reset [this newv]
(assert (number? newv) "Reset! G-Counter value must be a Number")
(swap! this (partial + (- newv @this)))
newv))
(defn g-counter []
(new G-Counter (atom {:id 0}) :id))
``` | 2017-11-21T17:51:19.000180 | Earlie |
clojurians | clojure | I don’t get what’s happening in `reset` but the rest looks better at a first glance | 2017-11-21T17:53:04.000120 | Margaret |
clojurians | clojure | Rreset needs to take the value the user wants the counter to be and find the difference between the that and the current value of the counter, then it adds that to the value in the map the user is allowed to modify. | 2017-11-21T17:54:48.000292 | Earlie |
clojurians | clojure | ```
(reset [this newv]
(assert (number? newv) "Reset! G-Counter value must be a Number")
(swap! this #(+ % (- newv @this)))
newv)
```
I had this originally. I suppose it's more readable. | 2017-11-21T17:55:30.000187 | Earlie |
clojurians | clojure | Can a swap function deref the atom it's swapping? | 2017-11-21T17:55:52.000153 | Earlie |
clojurians | clojure | It's weird, because derefing doesn't return the same value as the swap function accepts. | 2017-11-21T17:56:25.000388 | Earlie |
clojurians | clojure | I don’t know if that’s correct yet, but fyi you can always replace `(swap! a #(f % b))` with `(swap! a f b)` | 2017-11-21T17:56:33.000348 | Margaret |
clojurians | clojure | Oh yeah, good point. :thumbsup: | 2017-11-21T17:56:52.000015 | Earlie |
clojurians | clojure | Much cleaner | 2017-11-21T17:57:03.000132 | Earlie |
clojurians | clojure | Actually, swap does accept the current counter value. There's no need for the `@this` | 2017-11-21T17:57:45.000119 | Earlie |
clojurians | clojure | a deref of the same atom inside the function arg to swap! is safe because if the atom changes you will retry the swap! | 2017-11-21T17:57:53.000323 | Margaret |
clojurians | clojure | but yes, that too | 2017-11-21T17:58:08.000255 | Margaret |
clojurians | clojure | That's what I thought, which is why I hadn't thought about it. | 2017-11-21T17:58:29.000226 | Earlie |
clojurians | clojure | ```
(reset [this newv]
(assert (number? newv) "Reset! G-Counter value must be a Number")
;; (swap! this + (- newv @this))
(swap! this #(+ % (- newv %)))
newv)
``` | 2017-11-21T17:58:36.000247 | Earlie |
clojurians | clojure | ... I'm not sure why I'm doing this. It just needs to return the newv, and the swap! will handle the difference stuff. | 2017-11-21T18:00:41.000062 | Earlie |
clojurians | clojure | ```
(reset [this newv]
(assert (number? newv) "Reset! G-Counter value must be a Number")
(swap! this (constantly newv))
newv)
``` | 2017-11-21T18:01:48.000033 | Earlie |
clojurians | clojure | won’t the swap! call already return newv? | 2017-11-21T18:02:24.000507 | Margaret |
clojurians | clojure | Uh, yeah, it will. | 2017-11-21T18:02:42.000292 | Earlie |
clojurians | clojure | Well, that shrunk a lot... | 2017-11-21T18:02:48.000201 | Earlie |
clojurians | clojure | It feels a little weird to use swap for reset, though I suppose that allows me to keep the difference logic in the same place. | 2017-11-21T18:03:34.000311 | Earlie |
clojurians | clojure | I'm pretty happy with that.
For anyone interested:
```
(defn- swap-g-counter [this f & args]
(let [p (.p this)
n (.n this)]
(loop []
(let [oldval @this
newval (apply f oldval args)
pval @p
nval (update pval n + (- newval oldval))]
(assert (number? newval) "Swap! G-Counter function must return a Number")
(assert (>= newval oldval) "G-Counter is grow only")
(if (compare-and-set! p pval nval)
newval
(recur))))))
(deftype G-Counter [p n]
clojure.lang.IDeref
(deref [this]
(reduce + (vals p)))
clojure.lang.IAtom
(swap [this f]
(swap-g-counter this f))
(swap [this f a]
(swap-g-counter this f a))
(swap [this f a b]
(swap-g-counter this f a b))
(swap [this f a b args]
(apply swap-g-counter this f a b args))
(compareAndSet [this oldv newv]
(loop []
(let [pval @p]
(if (not= oldv (project-g-counter pval))
false
(or (compare-and-set! p pval (swap-g-counter pval n + (- newv oldv)))
(recur))))))
(reset [this newv]
(assert (number? newv) "Reset! G-Counter value must be a Number")
(swap! this (constantly newv))))
(defn g-counter []
(new G-Counter (atom {:id 0}) :id))
``` | 2017-11-21T18:05:23.000297 | Earlie |
clojurians | clojure | Thanks, <@Margaret>, <@Jonas>, <@Rebeca>!
I appreciate the help. | 2017-11-21T18:06:11.000051 | Earlie |
clojurians | clojure | how does the `deref` method work? isn’t `p` an atom? | 2017-11-21T18:13:01.000402 | Jonas |
clojurians | clojure | seems like calling `vals` on `p` in the deref method would throw an exception | 2017-11-21T18:14:13.000466 | Jonas |
clojurians | clojure | Yeah, that's a typo. I've fixed it:
```
clojure.lang.IDeref
(deref [this]
(reduce + (vals @p)))
``` | 2017-11-21T18:15:20.000247 | Earlie |
clojurians | clojure | I'm not sure when that got changed. | 2017-11-21T18:15:29.000193 | Earlie |
clojurians | clojure | i might be reading it wrong, but seems like there’s still a race condition in your `swap-g-counter` function | 2017-11-21T18:17:49.000013 | Jonas |
clojurians | clojure | the compare-and-set! will fail if p no longer olds pval | 2017-11-21T18:18:25.000094 | Margaret |
clojurians | clojure | that’s the point of using that function | 2017-11-21T18:18:30.000427 | Margaret |
clojurians | clojure | `p` is dereferenced twice | 2017-11-21T18:18:40.000369 | Jonas |
clojurians | clojure | inside a loop that retries if the compare-and-set! fails | 2017-11-21T18:18:52.000301 | Margaret |
clojurians | clojure | and the compare-and-set! will fail if p changes | 2017-11-21T18:19:18.000039 | Margaret |
clojurians | clojure | so if it changes between the 1st and 2nd dereference, but not between the 2nd dereference and `compare-and-set!` | 2017-11-21T18:19:26.000187 | Jonas |
clojurians | clojure | it would be inconsistent | 2017-11-21T18:19:30.000185 | Jonas |
clojurians | clojure | since the new value is derived from both the 1st and 2nd dereference | 2017-11-21T18:19:49.000234 | Jonas |
clojurians | clojure | and the first and second dereference might have different values | 2017-11-21T18:20:00.000294 | Jonas |
clojurians | clojure | no- if it changes between binding oldval and compare-and-set! the compare-and-set will fail | 2017-11-21T18:20:12.000080 | Margaret |
clojurians | clojure | `oldval` isn’t passed into `compare-and-set!`, `pval` is | 2017-11-21T18:20:43.000243 | Jonas |
clojurians | clojure | oh, tricky | 2017-11-21T18:21:05.000066 | Margaret |
clojurians | clojure | yeah, this is weird | 2017-11-21T18:21:08.000308 | Margaret |
clojurians | clojure | Yeah, I need to get a better naming convention. | 2017-11-21T18:21:33.000271 | Earlie |
clojurians | clojure | i think the code would be simplified a lot by having functions that work on immutable counter data | 2017-11-21T18:22:01.000191 | Jonas |
clojurians | clojure | I think you need nested compare-and-set! calls to ensure consistency on both dereferences? | 2017-11-21T18:22:16.000121 | Margaret |
clojurians | clojure | and using a plain ol’ atom to hold the data | 2017-11-21T18:22:18.000057 | Jonas |
clojurians | clojure | if you really wanted it to work with this interface, you could have `pval` use the data from the `oldval` dereference | 2017-11-21T18:23:02.000132 | Jonas |
clojurians | clojure | Yeah, I think I'm going to need to switch to immutable functions anyways for my merging logic.
At the moment I'd need to have a function which takes one of these and a p (from somewhere else) and merge them. I'd also need another function to get the p out to send elsewhere. | 2017-11-21T18:24:23.000413 | Earlie |
clojurians | clojure | the nice thing about atoms is that they just encapsulate identity. I don’t think you want to mix the identity and state pieces into one thing | 2017-11-21T18:24:49.000419 | Jonas |
clojurians | clojure | pval can't use oldval, because oldval is just an integer. | 2017-11-21T18:25:01.000243 | Earlie |
clojurians | clojure | Yeah, I think you're right. | 2017-11-21T18:25:36.000152 | Earlie |
clojurians | clojure | right, I guess you would have to have `oldval` derive from `pval` | 2017-11-21T18:25:40.000082 | Jonas |
clojurians | clojure | Good call, that's something that it could do. | 2017-11-21T18:25:58.000183 | Earlie |
clojurians | clojure | Though I'd need to bring back project-g-counter for the reduction function. | 2017-11-21T18:26:17.000450 | Earlie |
clojurians | clojure | yea | 2017-11-21T18:26:51.000123 | Jonas |
clojurians | clojure | or as long as you dereference `pval` before you do the dereference for `oldval`, it would work | 2017-11-21T18:28:19.000400 | Jonas |
clojurians | clojure | actually, nvmd | 2017-11-21T18:28:29.000238 | Jonas |
clojurians | clojure | i take that back | 2017-11-21T18:28:33.000062 | Jonas |
clojurians | clojure | I think you have to do it with a single dereference | 2017-11-21T18:29:06.000189 | Jonas |
clojurians | clojure | other wise it could change in between dereferences and then change back | 2017-11-21T18:29:21.000355 | Jonas |
clojurians | clojure | ```
(defn- swap-g-counter [this f & args]
(let [p (.p this)
n (.n this)]
(loop []
(let [pval @p
oldval (reduce + (vals pval))
newval (apply f oldval args)
nval (update pval n + (- newval oldval))]
(assert (number? newval) "Swap! G-Counter function must return a Number")
(assert (>= newval oldval) "G-Counter is grow only")
(if (compare-and-set! p pval nval)
newval
(recur))))))
``` | 2017-11-21T18:29:21.000388 | Earlie |
clojurians | clojure | Yeah, I'm pretty sure it's needed. | 2017-11-21T18:29:30.000197 | Earlie |
clojurians | clojure | :thumbsup: | 2017-11-21T18:30:17.000040 | Jonas |
clojurians | clojure | I'm using `wrap-json-response`, but I'd like to opt out and return `Content-Type: text/html` sometimes, is there an easy way out? | 2017-11-21T18:45:22.000067 | Lori |
clojurians | clojure | (oh, I'm working within Compojure-API) | 2017-11-21T18:45:37.000088 | Lori |
clojurians | clojure | so you have one endpoint, that would sometimes return json and sometimes return html? | 2017-11-21T18:52:03.000303 | Margaret |
clojurians | clojure | <@Margaret> correct, based on their request header of `Content-Type`, so they can have json or html | 2017-11-21T18:56:06.000355 | Lori |
clojurians | clojure | I think I need to just pull out this route from the main app, and add it back in separate without the offending middleware | 2017-11-21T18:56:42.000251 | Lori |
clojurians | clojure | is there a less awkward solution tho, perhaps? | 2017-11-21T18:56:53.000244 | Lori |
clojurians | clojure | there’s no rule saying you can’t generate json inside your handler (or have a conditional in your handler that either dispatches to an html function or a json function) | 2017-11-21T18:57:11.000055 | Margaret |
clojurians | clojure | (the ring function `content-type` was a no go) | 2017-11-21T18:57:12.000117 | Lori |
clojurians | clojure | those functions are just modifying data in a hash-map, if using them is at all awkward just skip them | 2017-11-21T18:57:34.000351 | Margaret |
clojurians | clojure | oh no, I mean, I'd like `wrap-json-X` most of the time, but on one route, reset it. I think what I'm setting is getting over-written though by the middleware | 2017-11-21T18:58:19.000116 | Lori |
clojurians | clojure | <@Lori>
I don’t know if that’s wrong, but when I need to return a different content-type I just change manually and return something like this:
{:status 200
:headers {“content-type” “text/html”}
:body {:message (:message (any-function))}} | 2017-11-21T18:58:47.000283 | Audie |
clojurians | clojure | yeah, if you want to conditionally make json you don’t want a middleware that always returns json | 2017-11-21T18:58:59.000380 | Margaret |
clojurians | clojure | if you do that, the content-type is changed? | 2017-11-21T18:59:12.000302 | Audie |
clojurians | clojure | that middleware isn’t doing as much as you think it is, just skip it | 2017-11-21T18:59:18.000073 | Margaret |
clojurians | clojure | here I’m using `wrap-json-response` as well | 2017-11-21T19:00:40.000009 | Audie |
clojurians | clojure | <@Audie> hm, I think it's not working, still debugging:
```
(-> (ok {:x y)
(assoc "headers" {"content-type" "text/html"}))
Content-Type: application/json; charset=utf-8
``` | 2017-11-21T19:03:09.000262 | Lori |
clojurians | clojure | How are configuring the handlers and middlewares of the app? can you put here? | 2017-11-21T19:22:23.000084 | Audie |
clojurians | clojure | this is weird, I've checked that I'm setting the header where the route is defined, and turned off all middleware, but the header is still reverting to `"application/json"` | 2017-11-21T19:24:22.000025 | Lori |
clojurians | clojure | the above isn't even valid code, so maybe start there before dumpling all the handlers and middlewares | 2017-11-21T19:24:30.000082 | Rebeca |
clojurians | clojure | "headers" isn't the right key | 2017-11-21T19:24:36.000029 | Rebeca |
clojurians | clojure | <https://github.com/ring-clojure/ring/blob/master/SPEC#L117> | 2017-11-21T19:24:53.000120 | Rebeca |
clojurians | clojure | (it helps to use the `ring.util.response` functions to make sure you're creating valid responses) | 2017-11-21T19:25:06.000207 | Daniell |
clojurians | clojure | <@Rebeca> apologies, I've mostly been using `(content-type "text/html")` | 2017-11-21T19:25:18.000184 | Lori |
clojurians | clojure | and <@Daniell> thanks, ya that fn is in `ring.util.response` | 2017-11-21T19:26:11.000073 | Lori |
clojurians | clojure | and <https://github.com/ring-clojure/ring-json/blob/master/src/ring/middleware/json.clj#L103-L112> clearly shows it doesn't check Content-Type at all to determine if it needs to encode | 2017-11-21T19:27:45.000242 | Rebeca |
clojurians | clojure | the docstring here <https://github.com/ring-clojure/ring-json/blob/master/src/ring/middleware/json.clj#L114-L128> says it only encodes vectors or maps | 2017-11-21T19:28:31.000123 | Rebeca |
clojurians | clojure | which of course doesn't match the actual behavior | 2017-11-21T19:28:48.000040 | Rebeca |
clojurians | clojure | <https://github.com/ring-clojure/ring-json/blob/master/src/ring/middleware/json.clj#L107> | 2017-11-21T19:28:49.000034 | Rebeca |
clojurians | clojure | <@Lori> And what exactly is your `ok` function doing? | 2017-11-21T19:53:35.000001 | Daniell |
clojurians | clojure | just returns a simple map (`ring.util.http-response/ok`)
```
(defn ok
"200 OK (Success)
OK"
([] (ok nil))
([body]
{:status 200
:headers {}
:body body}))
``` | 2017-11-21T19:54:39.000048 | Lori |
clojurians | clojure | Using your `ok` and `ring.util.response/content-type` and `ring-json`'s `ring.middleware.json/wrap-json-response` seems to work as expected: <https://www.dropbox.com/s/dzts47q5bwpg59x/Screenshot%202017-11-21%2016.57.17.png?dl=0> | 2017-11-21T19:58:02.000165 | Daniell |
clojurians | clojure | The `(assoc "headers" ...)` you had before, definitely would not work (as <@Rebeca> said) because it uses a string instead of a keyword. | 2017-11-21T19:58:56.000265 | Daniell |
clojurians | clojure | And even if you used `:headers`, you need to capitalize the header name for it to work. | 2017-11-21T20:00:30.000163 | Daniell |
clojurians | clojure | Anyways, did you get it sorted out in the end? Or are you still looking for input? <@Lori> | 2017-11-21T20:00:54.000305 | Daniell |
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