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同步進行多個地圖本地搜索

[英]Making multiple map local searches synchronously

 原文  2020-03-28 22:41:07  5   1    swift/ asynchronous/ mklocalsearchrequest

問題描述

我嘗試同步進行多個搜索（我的意思是一個接一個，在運行下一個之前等待上一個請求完成）並阻塞直到所有操作完成后再繼續。

但是一旦信號量放棄，本地搜索的完成句柄看起來就被阻塞並運行。 我做了很多嘗試都沒有成功。

我的代碼和日志如下（可以復制/粘貼到playground）：

import CoreLocation
import MapKit


func search(_ query: String, in span: MKCoordinateSpan, centered center: CLLocationCoordinate2D, id: Int) {

    let semaphore = DispatchSemaphore(value: 0)
    //let group = DispatchGroup(); group.enter()

    // Run the request for this rect
    print("\(#function): local search on the \(id)th portion ")

    let request = MKLocalSearch.Request()
    request.naturalLanguageQuery = query
    request.region = MKCoordinateRegion(center: center, span: span)

    if #available(iOS 13, *) {
        request.resultTypes = .pointOfInterest
    }


    let search = MKLocalSearch(request: request)

    search.start { response, error in
        print("\(id) got \(response?.mapItems.count) items")
        semaphore.signal()
    }


    let s = semaphore
    //let s = group

    // Wait for the request ot complete
    print("\(#function): waiting for the \(id)th portion to complete")
    //guard _ = s.wait(wallTimeout: .distantFuture) else {
    guard s.wait(timeout: .now() + 5) == .success else {
        print("\(#function): ***Warning: \(id)th timeout, job incomplete")
        return
    }

    print("\(#function): \(id)th completed")
}



let rect = CGRect(
    x: 48.10,
    y: 3.43,
    width: 0.09,
    height: 0.09
)


let n = 4
let latDelta = rect.width / CGFloat(n)
var latOffs = rect.minX



let queue = OperationQueue()
//queue.maxConcurrentOperationCount = 1
var ops = [BlockOperation]()

// -- Run all asyn loca search requests synchronuously
for i in 0..<n {
    // Take the next cut of the original region
    let portion = CGRect(
        x: latOffs,
        y: rect.minY,
        width: latDelta,
        height: rect.height
    )

    latOffs += latDelta

    ops.append(BlockOperation { [portion, i] in
        let center = CLLocationCoordinate2D(latitude: CLLocationDegrees(portion.midX), longitude: CLLocationDegrees(portion.midY))
        let span = MKCoordinateSpan(latitudeDelta: CLLocationDegrees(portion.width), longitudeDelta: CLLocationDegrees(portion.height))

        search("coffee", in: span, centered: center, id: i)
    })
}

queue.addOperations(ops, waitUntilFinished: true)

print("All done")

當前的虛假輸出：

search(_:in:centered:id:): local search on the 1th portion 
search(_:in:centered:id:): local search on the 2th portion 
search(_:in:centered:id:): local search on the 3th portion 
search(_:in:centered:id:): local search on the 0th portion 
search(_:in:centered:id:): waiting for the 1th portion to complete
search(_:in:centered:id:): waiting for the 3th portion to complete
search(_:in:centered:id:): waiting for the 2th portion to complete
search(_:in:centered:id:): waiting for the 0th portion to complete
search(_:in:centered:id:): ***Warning: 0th timeout, job incomplete
search(_:in:centered:id:): ***Warning: 2th timeout, job incomplete
search(_:in:centered:id:): ***Warning: 1th timeout, job incomplete
search(_:in:centered:id:): ***Warning: 3th timeout, job incomplete
All done
0 got Optional(10) items
2 got Optional(10) items
1 got Optional(10) items
3 got Optional(10) items

[更新]

預期的輸出應該顯示 no ***Warning和All done作為最后一行，如下（編號的確切順序取決於網絡條件）：

search(_:in:centered:id:): local search on the 1th portion 
search(_:in:centered:id:): local search on the 2th portion 
search(_:in:centered:id:): local search on the 3th portion 
search(_:in:centered:id:): local search on the 0th portion 
search(_:in:centered:id:): waiting for the 1th portion to complete
search(_:in:centered:id:): waiting for the 3th portion to complete
search(_:in:centered:id:): waiting for the 2th portion to complete
search(_:in:centered:id:): waiting for the 0th portion to complete
0 got Optional(10) items
search(_:in:centered:id:): 0th completed
2 got Optional(10) items
search(_:in:centered:id:): 2th completed
1 got Optional(10) items
search(_:in:centered:id:): 1th completed
3 got Optional(10) items
search(_:in:centered:id:): 3th completed
All done

[更新 2] 取消注釋行//queue.maxConcurrentOperationCount = 1時的輸出

search( :in:Centered:id:)：第0部分的本地搜索 2020-03-28 23:49:41 +0000 search( :in: Centered :id:)：等待第0部分完成 2020-03 -28 23:49:41 +0000 搜索( :in: central :id:): ***警告：第 0 次超時，作業未完成 2020-03-28 23:49:46 +0000 搜索( :in: central :id :)：第一部分的本地搜索 2020-03-28 23:49:46 +0000 search( :in: central :id:)：等待第一部分完成 2020-03-28 23:49:46 + 0000 search( :in:central:id:): ***警告：第 1 次超時，作業未完成 2020-03-28 23:49:51 +0000 search( :in: centric :id:)：2 號本地搜索部分 2020-03-28 23:49:51 +0000 搜索（ :in: Centered :id:）：等待第二部分完成 2020-03-28 23:49:51 +0000 搜索（ :in:centered: id:): ***警告: 第二次超時, 作業未完成 2020-03-28 23:49:56 +0000 搜索 ( :in: center :id:): 第三部分的本地搜索 2020-03-28 23: 49:56 +0000 搜索( :in: central :id:): 等待第三部分完成 2020-03-28 23:49:56 +0000 搜索( : in:central:id:): ***警告：第 3 次超時，作業未完成 2020-03-28 23:50:01 +0000 全部完成 2020-03-28 23:50:01 +0000 0 got Optional(10) items 2020-03-28 23:50:02 +0000 3 got Optional(10) items 2020-03-28 23:50:02 +0000 2 got Optional(10) items 2020-03-28 23:50:02 + 0000 1 得到 Optional(10) items 2020-03-28 23:50:02 +0000

注意：順便說一句，我還在每次打印的末尾添加了\\(Date())

1 個解決方案

解決方案1
 0 已采納  2020-03-28 22:49:49

如果您希望這些操作以串行方式運行，則必須指定隊列一次只能運行一個，例如

queue.maxConcurrentOperationCount = 1

而且，正如你發現，你要避免使用waitUntilFinished的選項addOperations ，為阻止當前線程，直到操作完成。 相反，使用完成處理程序模式。

這是我使用的代碼：

func performMultipleSearches(completion: @escaping () -> Void) {
    let searches = ["restaurant", "coffee", "hospital", "natural history museum"]

    let queue = OperationQueue()
    queue.maxConcurrentOperationCount = 1

    for (i, searchText) in searches.enumerated() {
        queue.addOperation {
            self.search(searchText, in: self.mapView.region, id: i)
        }
    }

    queue.addOperation {
        completion()
    }
}

func search(_ query: String, in region: MKCoordinateRegion, id: Int) {
    let semaphore = DispatchSemaphore(value: 0)

    os_log("%d starting", id)

    let request = MKLocalSearch.Request()
    request.naturalLanguageQuery = query
    request.region = region

    if #available(iOS 13, *) {
        request.resultTypes = .pointOfInterest
    }

    let search = MKLocalSearch(request: request)

    search.start { response, error in
        defer { semaphore.signal() }

        guard let mapItems = response?.mapItems else {
            os_log("  %d failed", id)
            return
        }

        os_log("  %d succeeded, found %d:", id, mapItems.count)
    }

    os_log("  %d waiting", id)
    guard semaphore.wait(timeout: .now() + 5) == .success else {
        os_log("  %d timedout", id)
        return
    }

    os_log("  %d done", id)
}

這產生了：

2020-03-28 16:16:25.219565-0700 MyApp[46601:2107182] 0 starting
2020-03-28 16:16:25.220018-0700 MyApp[46601:2107182]   0 waiting
2020-03-28 16:16:25.438121-0700 MyApp[46601:2107033]   0 succeeded, found 10:
2020-03-28 16:16:25.438269-0700 MyApp[46601:2107182]   0 done
2020-03-28 16:16:25.438436-0700 MyApp[46601:2107182] 1 starting
2020-03-28 16:16:25.438566-0700 MyApp[46601:2107182]   1 waiting
2020-03-28 16:16:25.639198-0700 MyApp[46601:2107033]   1 succeeded, found 10:
2020-03-28 16:16:25.639357-0700 MyApp[46601:2107182]   1 done
2020-03-28 16:16:25.639490-0700 MyApp[46601:2107182] 2 starting
2020-03-28 16:16:25.639598-0700 MyApp[46601:2107182]   2 waiting
2020-03-28 16:16:25.822085-0700 MyApp[46601:2107033]   2 succeeded, found 10:
2020-03-28 16:16:25.822274-0700 MyApp[46601:2107182]   2 done
2020-03-28 16:16:25.822422-0700 MyApp[46601:2107162] 3 starting
2020-03-28 16:16:25.822567-0700 MyApp[46601:2107162]   3 waiting
2020-03-28 16:16:26.015566-0700 MyApp[46601:2107033]   3 succeeded, found 1:
2020-03-28 16:16:26.015696-0700 MyApp[46601:2107162]   3 done
2020-03-28 16:16:26.015840-0700 MyApp[46601:2107162] all done

就其價值而言，我不會使用信號量，而是使用異步Operation子類。 例如，您可以使用此處定義的AsynchronousOperation類，然后執行以下操作：

class SearchOperation: AsynchronousOperation {
    let identifier: Int
    let searchText: String
    let region: MKCoordinateRegion

    init(identifier: Int, searchText: String, region: MKCoordinateRegion) {
        self.identifier = identifier
        self.searchText = searchText
        self.region = region

        super.init()
    }

    override func main() {
        os_log("%d started", identifier)

        let request = MKLocalSearch.Request()
        request.naturalLanguageQuery = searchText
        request.region = region

        if #available(iOS 13, *) {
            request.resultTypes = .pointOfInterest
        }

        let search = MKLocalSearch(request: request)

        search.start { response, error in
            defer { self.finish() }

            guard let mapItems = response?.mapItems else {
                os_log("  %d failed", self.identifier)
                return
            }

            os_log("  %d succeeded, found %d:", self.identifier, mapItems.count)
        }
    }
}

進而

let searches = ["restaurant", "coffee", "hospital", "natural history museum"]

let queue = OperationQueue()
queue.maxConcurrentOperationCount = 1

for (i, searchText) in searches.enumerated() {
    queue.addOperation(SearchOperation(identifier: i, searchText: searchText, region: mapView.region))
}

queue.addOperation {
    completion()
}

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