Fix crash when accessing setValue concurrently

[shota-nishizawa]

No description provided.

[ichiho-ojima]

Why is this type a class and not a struct?

[shota-nishizawa]

When I use ThreadSafeDictionary with struct, I get the error Escaping closure captures mutating 'self' parameter in subscript and removeValue.
It seems difficult to update self in a struct closure, so I use class.

struct ThreadSafeDictionary<V: Hashable,T>: Collection {
    private var dictionary: [V: T]
...
    subscript(key: V) -> T? {
        set(newValue) {
            self.concurrentQueue.async(flags: .barrier) {
                dictionary[key] = newValue   //   Error occurred: Escaping closure captures mutating 'self' parameter
            }
        }
        get {
            self.concurrentQueue.sync {
                return self.dictionary[key]
            }
        }
    }

...
    mutating func removeValue(forKey key: V) {
        self.concurrentQueue.async(flags: .barrier) {
            dictionary.removeValue(forKey: key)   //   Error occurred: Escaping closure captures mutating 'self' parameter
        }
    }
}

[ichiho-ojima]

Thank you for your explanation. Understood.

[ichiho-ojima]

Please unify the format of dictionary type declaration.

Suggested change

	private var dictionary: [V: T]
	private var dictionary: [V : T]

[shota-nishizawa]

Fixed by 7c1ad17.

[ichiho-ojima]

It looks like it hasn't been fixed.

[shota-nishizawa]

CI tests have passed.
https://github.com/cybozu/CachePropertyKit/actions/runs/8506365229

[ichiho-ojima]

Some of your code does not seem to be concurrency-safe.
To check, make the following changes to Package.swift, and then build it using Xcode 15.3 and Swift 5.10.

.target(
    name: "CachePropertyKit",
-    path: "Sources"
+    path: "Sources",
+    swiftSettings: [
+        .unsafeFlags([
+            "-Xfrontend", "-warn-concurrency",
+            "-Xfrontend", "-enable-actor-data-race-checks"
+        ])
+    ]
),

Note

The unsafe flags does not exist in upstream, because the use of unsafe flags makes the products containing this target ineligible for use by other packages.