ConcurrentDictionary öğeleri ekleme ve kaldırma

Bu örnekte bir öğesinden öğe ekleme, alma, güncelleştirme ve kaldırma gösterilmektedir System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>. Bu koleksiyon sınıfı iş parçacığı açısından güvenli bir uygulamadır. Öğelere eşzamanlı olarak erişmeye çalışan birden çok iş parçacığı olduğunda bunu kullanmanızı öneririz.

ConcurrentDictionary<TKey,TValue> , kodun veri eklemeye veya kaldırmaya çalışmadan önce bir anahtarın var olup olmadığını denetlemesini gereksiz hale getiren çeşitli kolaylık yöntemleri sağlar. Aşağıdaki tabloda bu kolaylık yöntemleri listelenerek bunların ne zaman kullanılacağı açıklanmaktadır.

Örnek

Aşağıdaki örnek, bir öğesine eşzamanlı olarak bazı öğeler ConcurrentDictionary<TKey,TValue> eklemek için iki Task örnek kullanır ve sonra öğelerin başarıyla eklendiğini göstermek için tüm içeriklerin çıkışını verir. Örnekte, koleksiyondaki AddOrUpdateöğeleri eklemek, güncelleştirmek ve GetOrAdd almak için , TryGetValueve yöntemlerinin nasıl kullanılacağı da gösterilmektedir.

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace DictionaryHowTo
{
    // The type of the Value to store in the dictionary.
    class CityInfo : IEqualityComparer<CityInfo>
    {
        public string Name { get; set; }
        public DateTime LastQueryDate { get; set; } = DateTime.Now;
        public decimal Longitude { get; set; } = decimal.MaxValue;
        public decimal Latitude { get; set; } = decimal.MaxValue;
        public int[] RecentHighTemperatures { get; set; } = new int[] { 0 };

        public bool Equals(CityInfo x, CityInfo y)
            => (x.Name, x.Longitude, x.Latitude) == 
                  (y.Name, y.Longitude, y.Latitude);

        public int GetHashCode(CityInfo cityInfo) =>
            cityInfo?.Name.GetHashCode() ?? throw new ArgumentNullException(nameof(cityInfo));
    }

    class Program
    {
        static readonly ConcurrentDictionary<string, CityInfo> Cities =
            new ConcurrentDictionary<string, CityInfo>(StringComparer.OrdinalIgnoreCase);

        static async Task Main()
        {
            CityInfo[] cityData =
            {
                new CityInfo { Name = "Boston", Latitude = 42.358769m, Longitude = -71.057806m, RecentHighTemperatures = new int[] { 56, 51, 52, 58, 65, 56,53} },
                new CityInfo { Name = "Miami", Latitude = 25.780833m, Longitude = -80.195556m, RecentHighTemperatures = new int[] { 86,87,88,87,85,85,86 } },
                new CityInfo { Name = "Los Angeles", Latitude = 34.05m, Longitude = -118.25m, RecentHighTemperatures =   new int[] { 67,68,69,73,79,78,78 } },
                new CityInfo { Name = "Seattle", Latitude = 47.609722m, Longitude =  -122.333056m, RecentHighTemperatures =   new int[] { 49,50,53,47,52,52,51 } },
                new CityInfo { Name = "Toronto", Latitude = 43.716589m, Longitude = -79.340686m, RecentHighTemperatures =   new int[] { 53,57, 51,52,56,55,50 } },
                new CityInfo { Name = "Mexico City", Latitude = 19.432736m, Longitude = -99.133253m, RecentHighTemperatures =   new int[] { 72,68,73,77,76,74,73 } },
                new CityInfo { Name = "Rio de Janeiro", Latitude = -22.908333m, Longitude = -43.196389m, RecentHighTemperatures =   new int[] { 72,68,73,82,84,78,84 } },
                new CityInfo { Name = "Quito", Latitude = -0.25m, Longitude = -78.583333m, RecentHighTemperatures =   new int[] { 71,69,70,66,65,64,61 } },
                new CityInfo { Name = "Milwaukee", Latitude = -43.04181m, Longitude = -87.90684m, RecentHighTemperatures =   new int[] { 32,47,52,64,49,44,56 } }
            };

            // Add some key/value pairs from multiple threads.
            await Task.WhenAll(
                Task.Run(() => TryAddCities(cityData)),
                Task.Run(() => TryAddCities(cityData)));

            static void TryAddCities(CityInfo[] cities)
            {
                for (var i = 0; i < cities.Length; ++i)
                {
                    var (city, threadId) = (cities[i], Thread.CurrentThread.ManagedThreadId);
                    if (Cities.TryAdd(city.Name, city))
                    {
                        Console.WriteLine($"Thread={threadId}, added {city.Name}.");
                    }
                    else
                    {
                        Console.WriteLine($"Thread={threadId}, could not add {city.Name}, it was already added.");
                    }
                }
            }

            // Enumerate collection from the app main thread.
            // Note that ConcurrentDictionary is the one concurrent collection
            // that does not support thread-safe enumeration.
            foreach (var city in Cities)
            {
                Console.WriteLine($"{city.Key} has been added.");
            }

            AddOrUpdateWithoutRetrieving();
            TryRemoveCity();
            RetrieveValueOrAdd();
            RetrieveAndUpdateOrAdd();

            Console.WriteLine("Press any key.");
            Console.ReadKey();
        }

        // This method shows how to add key-value pairs to the dictionary
        // in scenarios where the key might already exist.
        static void AddOrUpdateWithoutRetrieving()
        {
            // Sometime later. We receive new data from some source.
            var ci = new CityInfo
            {
                Name = "Toronto",
                Latitude = 43.716589M,
                Longitude = -79.340686M,
                RecentHighTemperatures = new int[] { 54, 59, 67, 82, 87, 55, -14 }
            };

            // Try to add data. If it doesn't exist, the object ci is added. If it does
            // already exist, update existingVal according to the custom logic.
            _ = Cities.AddOrUpdate(
                ci.Name,
                ci,
                (cityName, existingCity) =>
                {
                    // If this delegate is invoked, then the key already exists.
                    // Here we make sure the city really is the same city we already have.
                    if (ci != existingCity)
                    {
                        // throw new ArgumentException($"Duplicate city names are not allowed: {ci.Name}.");
                    }

                    // The only updatable fields are the temperature array and LastQueryDate.
                    existingCity.LastQueryDate = DateTime.Now;
                    existingCity.RecentHighTemperatures = ci.RecentHighTemperatures;

                    return existingCity;
                });

            // Verify that the dictionary contains the new or updated data.
            Console.Write($"Most recent high temperatures for {ci.Name} are: ");
            var temps = Cities[ci.Name].RecentHighTemperatures;
            Console.WriteLine(string.Join(", ", temps));
        }

        // This method shows how to use data and ensure that it has been
        // added to the dictionary.
        static void RetrieveValueOrAdd()
        {
            var searchKey = "Caracas";
            CityInfo retrievedValue = null;

            try
            {
                retrievedValue = Cities.GetOrAdd(searchKey, GetDataForCity(searchKey));
            }
            catch (ArgumentException e)
            {
                Console.WriteLine(e.Message);
            }

            // Use the data.
            if (retrievedValue != null)
            {
                Console.Write($"Most recent high temperatures for {retrievedValue.Name} are: ");
                var temps = Cities[retrievedValue.Name].RecentHighTemperatures;
                Console.WriteLine(string.Join(", ", temps));
            }
        }

        // This method shows how to remove a value from the dictionary.
        // If the value is unable to be removed, you can handle that by using the return
        // boolean value from the .TryRemove function.
        static void TryRemoveCity()
        {
            Console.WriteLine($"Total cities = {Cities.Count}");

            var searchKey = "Milwaukee";
            if (Cities.TryRemove(searchKey, out CityInfo retrievedValue))
            {
                Console.Write($"Most recent high temperatures for {retrievedValue.Name} are: ");
                var temps = retrievedValue.RecentHighTemperatures;
                Console.WriteLine(string.Join(", ", temps));
            }
            else
            {
                Console.WriteLine($"Unable to remove {searchKey}");
            }

            Console.WriteLine($"Total cities = {Cities.Count}");
        }

        // This method shows how to retrieve a value from the dictionary,
        // when you expect that the key/value pair already exists,
        // and then possibly update the dictionary with a new value for the key.
        static void RetrieveAndUpdateOrAdd()
        {
            var searchKey = "Buenos Aires";
            if (Cities.TryGetValue(searchKey, out CityInfo retrievedValue))
            {
                // Use the data.
                Console.Write($"Most recent high temperatures for {retrievedValue.Name} are: ");
                var temps = retrievedValue.RecentHighTemperatures;
                Console.WriteLine(string.Join(", ", temps));

                // Make a copy of the data. Our object will update its LastQueryDate automatically.
                var newValue = new CityInfo
                {
                    Name = retrievedValue.Name,
                    Latitude = retrievedValue.Latitude,
                    Longitude = retrievedValue.Longitude,
                    RecentHighTemperatures = retrievedValue.RecentHighTemperatures
                };

                // Replace the old value with the new value.
                if (!Cities.TryUpdate(searchKey, newValue, retrievedValue))
                {
                    // The data was not updated. Log error, throw exception, etc.
                    Console.WriteLine($"Could not update {retrievedValue.Name}");
                }
            }
            else
            {
                // Add the new key and value. Here we call a method to retrieve
                // the data. Another option is to add a default value here and
                // update with real data later on some other thread.
                var newValue = GetDataForCity(searchKey);
                if (Cities.TryAdd(searchKey, newValue))
                {
                    // Use the data.
                    Console.Write($"Most recent high temperatures for {newValue.Name} are: ");
                    var temps = newValue.RecentHighTemperatures;
                    Console.WriteLine(string.Join(", ", temps));
                }
                else
                {
                    Console.WriteLine($"Unable to add data for {searchKey}");
                }
            }
        }

        // Assume this method knows how to find long/lat/temp info for any specified city.
        static CityInfo GetDataForCity(string name) => name switch
        {
            "Caracas" => new CityInfo
            {
                Name = "Caracas",
                Longitude = 10.5M,
                Latitude = -66.916667M,
                RecentHighTemperatures = new int[] { 91, 89, 91, 91, 87, 90, 91 }
            },
            "Buenos Aires" => new CityInfo
            {
                Name = "Buenos Aires",
                Longitude = -34.61M,
                Latitude = -58.369997M,
                RecentHighTemperatures = new int[] { 80, 86, 89, 91, 84, 86, 88 }
            },
            _ => throw new ArgumentException($"Cannot find any data for {name}")
        };
    }
}

Imports System.Collections.Concurrent
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks

Namespace DictionaryHowToVB

    ' The type of the value to store in the dictionary.
    Class CityInfo
        Public Property Name As String
        Public Property LastQueryDate As DateTime
        Public Property Longitude As Decimal
        Public Property Latitude As Decimal
        Public Property RecentHighTemperatures As Integer()

        Public Sub New()
        End Sub

        Public Sub New(key As String)
            Name = key
            ' MaxValue means "not initialized".
            Longitude = Decimal.MaxValue
            Latitude = Decimal.MaxValue
            LastQueryDate = DateTime.Now
            RecentHighTemperatures = {0}
        End Sub

        Public Sub New(name As String, longitude As Decimal, latitude As Decimal, temps As Integer())
            Me.Name = name
            Me.Longitude = longitude
            Me.Latitude = latitude
            RecentHighTemperatures = temps
        End Sub
    End Class

    Class Program
        ' Create a new concurrent dictionary with the specified concurrency level and capacity.
        Shared cities As New ConcurrentDictionary(Of String, CityInfo)(System.Environment.ProcessorCount, 10)

        Shared Sub Main()

            Dim data As CityInfo() =
                {New CityInfo With {.Name = "Boston", .Latitude = 42.358769, .Longitude = -71.057806, .RecentHighTemperatures = {56, 51, 52, 58, 65, 56, 53}},
                    New CityInfo With {.Name = "Miami", .Latitude = 25.780833, .Longitude = -80.195556, .RecentHighTemperatures = {86, 87, 88, 87, 85, 85, 86}},
                    New CityInfo With {.Name = "Los Angeles", .Latitude = 34.05, .Longitude = -118.25, .RecentHighTemperatures = {67, 68, 69, 73, 79, 78, 78}},
                    New CityInfo With {.Name = "Seattle", .Latitude = 47.609722, .Longitude = -122.333056, .RecentHighTemperatures = {49, 50, 53, 47, 52, 52, 51}},
                    New CityInfo With {.Name = "Toronto", .Latitude = 43.716589, .Longitude = -79.340686, .RecentHighTemperatures = {53, 57, 51, 52, 56, 55, 50}},
                    New CityInfo With {.Name = "Mexico City", .Latitude = 19.432736, .Longitude = -99.133253, .RecentHighTemperatures = {72, 68, 73, 77, 76, 74, 73}},
                    New CityInfo With {.Name = "Rio de Janiero", .Latitude = -22.908333, .Longitude = -43.196389, .RecentHighTemperatures = {72, 68, 73, 82, 84, 78, 84}},
                    New CityInfo With {.Name = "Quito", .Latitude = -0.25, .Longitude = -78.583333, .RecentHighTemperatures = {71, 69, 70, 66, 65, 64, 61}}}

            '  Add some key/value pairs from multiple threads.
            Dim tasks(1) As Task

            tasks(0) = Task.Run(Sub()
                                    For i As Integer = 0 To 1
                                        If cities.TryAdd(data(i).Name, data(i)) Then
                                            Console.WriteLine($"Added {data(i).Name} on thread {Thread.CurrentThread.ManagedThreadId}")
                                        Else
                                            Console.WriteLine($"Could not add {data(i)}")
                                        End If
                                    Next
                                End Sub)

            tasks(1) = Task.Run(Sub()
                                    For i As Integer = 2 To data.Length - 1
                                        If cities.TryAdd(data(i).Name, data(i)) Then
                                            Console.WriteLine($"Added {data(i).Name} on thread {Thread.CurrentThread.ManagedThreadId}")
                                        Else
                                            Console.WriteLine($"Could not add {data(i)}")
                                        End If
                                    Next
                                End Sub)

            ' Output results so far.
            Task.WaitAll(tasks)

            ' Enumerate data on main thread. Note that
            ' ConcurrentDictionary is the one collection class
            ' that does not support thread-safe enumeration.
            For Each city In cities
                Console.WriteLine($"{city.Key} has been added")
            Next

            AddOrUpdateWithoutRetrieving()
            RetrieveValueOrAdd()
            RetrieveAndUpdateOrAdd()

            Console.WriteLine("Press any key")
            Console.ReadKey()

        End Sub

        ' This method shows how to add key-value pairs to the dictionary
        ' in scenarios where the key might already exist.
        Private Shared Sub AddOrUpdateWithoutRetrieving()
            ' Sometime later. We receive new data from some source.
            Dim ci As New CityInfo With {.Name = "Toronto", .Latitude = 43.716589, .Longitude = -79.340686, .RecentHighTemperatures = {54, 59, 67, 82, 87, 55, -14}}

            ' Try to add data. If it doesn't exist, the object ci is added. If it does
            ' already exist, update existingVal according to the custom logic in the 
            ' delegate.
            cities.AddOrUpdate(ci.Name, ci, Function(key, existingVal)
                                                ' If this delegate is invoked, then the key already exists.
                                                ' Here we make sure the city really is the same city we already have.
                                                ' (Support for multiple keys of the same name is left as an exercise for the reader.)
                                                If (ci.Name = existingVal.Name And ci.Longitude = existingVal.Longitude) = False Then
                                                    Throw New ArgumentException($"Duplicate city names are not allowed: {ci.Name}.")
                                                End If
                                                ' The only updatable fields are the temperature array and LastQueryDate.
                                                existingVal.LastQueryDate = DateTime.Now
                                                existingVal.RecentHighTemperatures = ci.RecentHighTemperatures
                                                Return existingVal
                                            End Function)

            ' Verify that the dictionary contains the new or updated data.
            Console.Write($"Most recent high temperatures for {cities(ci.Name).Name} are: ")
            Dim temps = cities(ci.Name).RecentHighTemperatures
            For Each temp In temps
                Console.Write($"{temp}, ")
            Next

            Console.WriteLine()

        End Sub

        'This method shows how to use data and ensure that it has been
        ' added to the dictionary.
        Private Shared Sub RetrieveValueOrAdd()
            Dim searchKey = "Caracas"
            Dim retrievedValue As CityInfo = Nothing

            Try
                retrievedValue = cities.GetOrAdd(searchKey, GetDataForCity(searchKey))

            Catch e As ArgumentException
                Console.WriteLine(e.Message)
            End Try

            ' Use the data.
            If Not retrievedValue Is Nothing Then
                Console.WriteLine($"Most recent high temperatures for {retrievedValue.Name} are: ")
                Dim temps = cities(retrievedValue.Name).RecentHighTemperatures
                For Each temp In temps
                    Console.Write($"{temp}, ")
                Next
            End If
            Console.WriteLine()

        End Sub

        ' This method shows how to retrieve a value from the dictionary,
        ' when you expect that the key/value pair already exists,
        ' and then possibly update the dictionary with a new value for the key.
        Private Shared Sub RetrieveAndUpdateOrAdd()
            Dim retrievedValue As New CityInfo()
            Dim searchKey = "Buenos Aires"

            If (cities.TryGetValue(searchKey, retrievedValue)) Then

                ' Use the data.
                Console.Write($"Most recent high temperatures for {retrievedValue.Name} are: ")
                Dim temps = retrievedValue.RecentHighTemperatures
                For Each temp In temps
                    Console.Write($"{temp}, ")
                Next
                ' Make a copy of the data. Our object will update its LastQueryDate automatically.
                Dim newValue As New CityInfo(retrievedValue.Name,
                                                        retrievedValue.Longitude,
                                                        retrievedValue.Latitude,
                                                        retrievedValue.RecentHighTemperatures)

            Else
                Console.WriteLine($"Unable to find data for {searchKey}")
            End If
        End Sub

        ' Assume this method knows how to find long/lat/temp info for any specified city.
        Private Shared Function GetDataForCity(searchKey As String) As CityInfo
            ' Real implementation left as exercise for the reader.
            If String.CompareOrdinal(searchKey, "Caracas") = 0 Then
                Return New CityInfo() With {.Name = "Caracas",
                                            .Longitude = 10.5,
                                            .Latitude = -66.916667,
                                            .RecentHighTemperatures = {91, 89, 91, 91, 87, 90, 91}}
            ElseIf String.CompareOrdinal(searchKey, "Buenos Aires") = 0 Then
                Return New CityInfo() With {.Name = "Buenos Aires",
                                            .Longitude = -34.61,
                                            .Latitude = -58.369997,
                                            .RecentHighTemperatures = {80, 86, 89, 91, 84, 86, 88}}
            Else
                Throw New ArgumentException($"Cannot find any data for {searchKey}")

            End If
        End Function
    End Class
End Namespace

ConcurrentDictionary<TKey,TValue> çok iş parçacıklı senaryolar için tasarlanmıştır. Koleksiyona öğe eklemek veya koleksiyondan öğe kaldırmak için kodunuzda kilitleri kullanmanız gerekmez. Ancak, bir iş parçacığının bir değeri alması ve başka bir iş parçacığının aynı anahtara yeni bir değer vererek koleksiyonu hemen güncelleştirmesi her zaman mümkündür.

Ayrıca, tüm yöntemleri ConcurrentDictionary<TKey,TValue> iş parçacığı açısından güvenli olsa da, özellikle GetOrAdd ve AddOrUpdatetüm yöntemler atomik değildir. Bilinmeyen kodun tüm iş parçacıklarını engellemesini önlemek için, bu yöntemlere geçirilen kullanıcı temsilcisi sözlüğün iç kilidinin dışında çağrılır. Bu nedenle, bu olay dizisinin gerçekleşmesi mümkündür:

1. threadA çağrıları GetOrAdd, hiçbir öğeyi bulmaz ve temsilciyi çağırarak valueFactory eklenecek yeni bir öğe oluşturur.

2. threadB eşzamanlı olarak çağrılırGetOrAdd, temsilcisi valueFactory çağrılır ve threadA'nın önce iç kilidine ulaşır ve böylece yeni anahtar-değer çifti sözlüğe eklenir.

3. threadA'nın kullanıcı temsilcisi tamamlar ve iş parçacığı kilide ulaşır, ancak artık öğenin zaten var olduğunu görür.

4. threadA bir "Get" gerçekleştirir ve daha önce threadB tarafından eklenen verileri döndürür.

Bu nedenle, tarafından GetOrAdd döndürülen verilerin iş parçacığının valueFactorytarafından oluşturulan veriyle aynı olması garanti değildir. Çağrıldığında AddOrUpdate benzer bir olay dizisi oluşabilir.

Ayrıca bkz.

• System.Collections.Concurrent
• İş Parçacığı Güvenli Koleksiyonları