我相信 XCode 错误地报告了我的 Swift Access Race SynchronizedDictionary
- 或者是吗?
我的SynchronizedDictionary
样子是这样的:
public struct SynchronizedDictionary<K: Hashable, V> {
private var dictionary = [K: V]()
private let queue = DispatchQueue(
label: "SynchronizedDictionary",
qos: DispatchQoS.userInitiated,
attributes: [DispatchQueue.Attributes.concurrent]
)
public subscript(key: K) -> V? {
get {
return queue.sync {
return self.dictionary[key]
}
}
mutating set {
queue.sync(flags: .barrier) {
self.dictionary[key] = newValue
}
}
}
}
以下测试代码将触发“Swift Access Race”问题(当为方案打开 Thread Sanitizer 时):
var syncDict = SynchronizedDictionary<String, String>()
let setExpectation = XCTestExpectation(description: "set_expectation")
let getExpectation = XCTestExpectation(description: "get_expectation")
let queue = DispatchQueue(label: "SyncDictTest", qos: .background, attributes: [.concurrent])
queue.async {
for i in 0...100 {
syncDict["\(i)"] = "\(i)"
}
setExpectation.fulfill()
}
queue.async {
for i in 0...100 {
_ = syncDict["\(i)"]
}
getExpectation.fulfill()
}
self.wait(for: [setExpectation, getExpectation], timeout: 30)
Swift Race Access 如下所示:
我真的没想到这里会有访问竞争条件,因为SynchronizedDictionary
应该处理并发。
我可以通过在测试中将获取和设置包装在类似于实际实现的 DispatchQueue 中来解决此问题SynchronizedDictionary
:
let accessQueue = DispatchQueue(
label: "AccessQueue",
qos: DispatchQoS.userInitiated,
attributes: [DispatchQueue.Attributes.concurrent]
)
var syncDict = SynchronizedDictionary<String, String>()
let setExpectation = XCTestExpectation(description: "set_expectation")
let getExpectation = XCTestExpectation(description: "get_expectation")
let queue = DispatchQueue(label: "SyncDictTest", qos: .background, attributes: [.concurrent])
queue.async {
for i in 0...100 {
accessQueue.sync(flags: .barrier) {
syncDict["\(i)"] = "\(i)"
}
}
setExpectation.fulfill()
}
queue.async {
for i in 0...100 {
accessQueue.sync {
_ = syncDict["\(i)"]
}
}
getExpectation.fulfill()
}
self.wait(for: [setExpectation, getExpectation], timeout: 30)
...但这已经发生在内部SynchronizedDictionary
- 那么为什么 Xcode 报告访问竞争条件?- Xcode 有错,还是我遗漏了什么?