Add `SystemProperties` #3924

massimosiani · 2024-01-01T10:34:45Z

Addresses #3313.

djspiewak · 2024-01-03T17:27:48Z

Thank you for looking at this! An interesting question for us to answer though is what we want to do with Native and JavaScript. This is a bit different from Env, which works on all three platforms (with the exception of in-browser JS).

armanbilge · 2024-01-03T17:47:57Z

Native and JavaScript

They both support System properties. It's basically just a global mutable map.

durban · 2024-01-04T15:29:04Z

A question: the getAndSet, modify, and similar methods look like the ones on Ref. However, here they are not atomic, right? So having them could be somewhat misleading. (While having only get and set would make it clear, that there is no atomicity for modification.)

massimosiani · 2024-01-04T20:51:54Z

I would agree. TBH, I wondered whether we should try and make them atomic, but that's probably not something you'd expect by system props.

durban · 2024-01-05T20:26:37Z

I don't think we can make them atomic. Or do you know a way?

massimosiani · 2024-01-06T10:10:59Z

Right, not sure how could be made atomic. Citing Arman, it's basically just a global mutable map.
I'll remove getAndSet and getAndUpdate but I think that update is still useful if we make clear that there are no guarantees about concurrent modifications. It's a handy wrapper for a get followed by set. I also like modify as a wrapper but would like to hear other opinions.

armanbilge · 2024-01-06T16:36:33Z

I think that update is still useful if we make clear that there are no guarantees about concurrent modifications

Unfortunately I think it's still confusing. Anyway, I expect 99% of usecases to just be reading system properties. APIs that require setting/updating system properties seem really dicey 🙄

durban · 2024-01-06T18:01:52Z

I'd just go with get, set and remove. If that's the functionality offered by the platform, and we can't provide atomicity, its best simply to wrap those.

armanbilge · 2024-01-06T18:07:12Z

Similar to Env, we can also add something to list/iterate the keys/entries.

durban · 2024-01-09T23:16:42Z

std/shared/src/main/scala/cats/effect/std/Prop.scala

+   */
+  def unset(key: String): F[Unit]
+
+  def entries: F[Properties]


I'm not sure I like returning a mutable object here. (I think we usually try to avoid that?)

For Env we decided to return an Iterable[(String, String)], but that was because of case-sensitivity issues which I don't think apply here. So probably makes most sense to return an immutable Map[String, String].

durban

I think the entries is not an atomic snapshot of the system properties. it would be nice if we could do that, but I don't think it's possible with the available JDK API.

durban · 2024-06-04T22:15:25Z

std/shared/src/main/scala/cats/effect/std/Prop.scala

+      F.delay(Option(System.getProperty(key))) // thread-safe
+
+    def set(key: String, value: String): F[Unit] =
+      F.void(F.delay(System.setProperty(key, value)))


If I'm reading the JDK source correctly, this eventually calls a synchronized method. So, technically, it should be F.blocking. I don't know if we care about this though...

Yes, that's right. I think we should do that.

Suggested change

F.void(F.delay(System.setProperty(key, value)))

F.void(F.blocking(System.setProperty(key, value)))

durban · 2024-06-04T22:20:16Z

std/shared/src/main/scala/cats/effect/std/Prop.scala

+    @nowarn3("cat=deprecation")
+    def entries: F[Map[String, String]] = {
+      import scala.collection.JavaConverters._
+      F.delay(Map.empty ++ System.getProperties().asScala)


Similarly, I think this calls into a Collections.synchronizedSet, so technically should be blocking. (Although this should be uncontended, I think. So we probably care even less...)

durban · 2024-06-04T22:20:59Z

tests/shared/src/test/scala/cats/effect/std/PropSpec.scala

+      for {
+        _ <- Prop[IO].set("some property", "the value")
+        props <- Prop[IO].entries
+        assertion <- IO(props mustEqual System.getProperties())


There is a test failure here, I think it's just because we're comparing a Scala Map with a Java hashtable.

durban · 2024-06-04T22:26:25Z

std/shared/src/main/scala/cats/effect/std/Prop.scala

+
+import scala.collection.immutable.Map
+
+trait Prop[F[_]] { self =>


Maybe we should make this sealed, just for future-proofing?

On the other hand, this prevents mocking. Our current practice is not really to sealed anything, for better or for worse 🤷

TonioGela · 2024-06-30T17:55:14Z

[BIKESHEDDING] I'm late to the party to comment probably, but I fear that Prop[F] as a name may clash with scalacheck or one of its integrations.

armanbilge · 2024-07-15T17:38:46Z

but I fear that Prop[F] as a name may clash with scalacheck or one of its integrations.

I actually also dislike the name Prop[F], without even considering the Scalacheck issues (good point).

The reason that I dislike it is because this API is very specifically abstracting over the (global singleton) system properties, not the generic JDK Properties datatype.

If we want to keep the name short we could rename to SysProps[F] perhaps. Or just go for SystemProperties[F] which I think is my preference.

armanbilge · 2024-07-15T18:14:54Z

I think the entries is not an atomic snapshot of the system properties. it would be nice if we could do that, but I don't think it's possible with the available JDK API.

The JDK suggests there is some notion of "bulk" operations.

    /**
     * Properties does not store values in its inherited Hashtable, but instead
     * in an internal ConcurrentHashMap.  Synchronization is omitted from
     * simple read operations.  Writes and bulk operations remain synchronized,
     * as in Hashtable.
     */

https://github.com/openjdk/jdk/blob/388fcf03c02c41bb690733e8565642c24ead56e0/src/java.base/share/classes/java/util/Properties.java#L161-L167

I am still trying to figure out what the bulk operations are exactly. If serializing the properties to a stream is one such bulk operation, perhaps we can use that to make an atomic copy first ... 🤔

armanbilge · 2024-07-15T19:29:06Z

I think the entries is not an atomic snapshot of the system properties. it would be nice if we could do that, but I don't think it's possible with the available JDK API.

It is possible, I think I was able to fix it. Thanks for catching :)

armanbilge · 2024-07-22T18:57:10Z

std/shared/src/main/scala/cats/effect/std/Prop.scala

+        import scala.collection.JavaConverters._
+        val props = System.getProperties
+        val back = new java.util.HashMap[String, String](props.size())
+        props.putAll(back)


Aw crap, I think I got this backwards 😕 it should be back.putAll(props) but then it's no longer atomic which was the point of copying. Hmm.

massimosiani · 2024-07-30T13:42:42Z

Or just go for SystemProperties[F] which I think is my preference.

That's my favorite too.

std/shared/src/main/scala/cats/effect/std/SystemProperties.scala

armanbilge · 2024-11-21T17:28:57Z

After going through a few iterations, I think we should just stick to get/set/clear.

Technically Properties extends Hashtable, and it is possible to implement a MapRef for Hashtable. But actually it extends Hashtable[Object, Object], and the Properties-specific APIs add special handling for non-String values and defaults. Anyway, it's a bit of a mess, and I really don't see a compelling usecase for atomic modification of Properties.

This reverts commit 99de034.

massimosiani added 4 commits December 31, 2023 18:18

write the Prop interface

72704b1

sbt prePR

4b8144a

add more tests

0385959

randomize the test key

030915f

djspiewak added the 🍄 enhancement label Jan 3, 2024

remove non-atomic functions

fe589e6

durban reviewed Jan 9, 2024

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use an immutable map

cbad5e5

armanbilge added this to the v3.6.0 milestone May 20, 2024

armanbilge closed this May 20, 2024

armanbilge reopened this May 20, 2024

armanbilge added 3 commits May 27, 2024 14:48

Merge remote-tracking branch 'upstream/series/3.x' into feature/prop

dd20429

Update headers

49fa3b2

Fix compile on 2.12

1e2bf07

durban reviewed Jun 4, 2024

View reviewed changes

armanbilge added 2 commits July 15, 2024 11:15

Use blocking when setting a property

967ca63

Make entries atomic

f570b7e

armanbilge marked this pull request as draft July 15, 2024 19:28

armanbilge reviewed Jul 22, 2024

View reviewed changes

massimosiani and others added 3 commits July 30, 2024 16:22

compare the same types

923c0d5

Fix deprecations in test

9436fd6

Prop -> SystemProperties

4a71b85

armanbilge force-pushed the feature/prop branch from 8bf996e to 4a71b85 Compare August 8, 2024 05:59

armanbilge added 3 commits August 8, 2024 06:05

Formatting

638a1fb

Merge remote-tracking branch 'upstream/series/3.x' into feature/prop

51c219f

SystemProperties is a MapRef

99de034

iRevive reviewed Nov 1, 2024

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std/shared/src/main/scala/cats/effect/std/SystemProperties.scala Outdated Show resolved Hide resolved

armanbilge added 2 commits November 21, 2024 17:31

Revert "SystemProperties is a MapRef"

fcd5410

This reverts commit 99de034.

Simplify and fixup

3eaa25b

armanbilge changed the title ~~Feature/prop~~ Add SystemProperties Nov 21, 2024

armanbilge marked this pull request as ready for review November 21, 2024 17:53

djspiewak approved these changes Nov 21, 2024

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djspiewak merged commit 8c305d7 into typelevel:series/3.x Nov 21, 2024
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Add `SystemProperties` #3924

Add `SystemProperties` #3924

massimosiani commented Jan 1, 2024

djspiewak commented Jan 3, 2024

armanbilge commented Jan 3, 2024

durban commented Jan 4, 2024

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armanbilge commented Nov 21, 2024

	F.void(F.delay(System.setProperty(key, value)))
	F.void(F.blocking(System.setProperty(key, value)))


		import scala.collection.immutable.Map

		trait Prop[F[_]] { self =>

Add SystemProperties #3924

Add SystemProperties #3924

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Add `SystemProperties` #3924

Add `SystemProperties` #3924

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