:Fondation Erwin Mayer

If you make a request for data which results in a lot of events generated by Bloomberg API (such as long historical intraday data request, or possibly real time subscriptions), do not use the pattern specified in the API documentation, as it may end up making your application very slow to retrieve all events. Basically, do not call NextEvent() on a Session object, use a dedicated EventQueue instead.

Instead of doing this:

var cID = new CorrelationID(1);
session.SendRequest(request, cID);
do {
   Event eventObj = session.NextEvent();
   ...
}

Do this:

var cID = new CorrelationID(1);
var eventQueue = new EventQueue();
session.SendRequest(request, eventQueue, cID);
do {
   Event eventObj = eventQueue.NextEvent();
   ...
}

This simple change may yield performance improvements by an order of magnitude (or not, as the API is known to not be particularly deterministic…).

If you need to flatten ordered enumerables, that is taking one element of each enumerable, in order, to flatten a combination, here is a quick solution in C# and VB.NET, accompanied with an example:

Code in VB.NET:

Private Shared Sub GetCombinationsRec(Of T)(sources As IList(Of IEnumerable(Of T)), chain As T(), index As Integer, combinations As ICollection(Of T()))
	For Each element As var In sources(index)
		chain(index) = element
		If index Is sources.Count - 1 Then
			Dim finalChain = New T(chain.Length - 1) {}
			chain.CopyTo(finalChain, 0)
			combinations.Add(finalChain)
		Else
			GetCombinationsRec(sources := sources, chain := chain, index := index + 1, combinations := combinations)
		End If
	Next
End Sub

Public Shared Function GetCombinations(Of T)(ParamArray enumerables As IEnumerable(Of T)()) As List(Of T())
	Dim combinations = New List(Of T())(enumerables.Length)
	If enumerables.Length > 0 Then
		Dim chain = New T(enumerables.Length - 1) {}
		GetCombinationsRec(sources := enumerables, chain := chain, index := 0, combinations := combinations)
	End If
	Return combinations
End Function

Code in C#.NET:

private static void GetCombinationsRec<T>(IList<IEnumerable<T>> sources, T[] chain, int index, ICollection<T[]> combinations) {
	foreach (var element in sources[index]) {
		chain[index] = element;
		if (index == sources.Count - 1) {
			var finalChain = new T[chain.Length];
			chain.CopyTo(finalChain, 0);
			combinations.Add(finalChain);
		}
		else {
			GetCombinationsRec(sources: sources, chain: chain, index: index + 1, combinations: combinations);
		}
	}
}

public static List<T[]> GetCombinations<T>(params IEnumerable<T>[] enumerables) {
	var combinations = new List<T[]>(enumerables.Length);
	if (enumerables.Length > 0) {
		var chain = new T[enumerables.Length];
		GetCombinationsRec(sources: enumerables, chain: chain, index: 0, combinations: combinations);
	}
	return combinations;
}

Usage is simple:

Dim list1 = New String() {"hello", "bonjour", "hallo", "hola"}
Dim list2 = New String() {"Erwin", "Larry", "Bill", "Steve"}
Dim list3 = New String() {"!", ".."}
Dim result = Utils.GetCombinations(list1, list2, list3)
For Each r In result
    Debug.Print(String.Join(" "c, r))
Next

or in C#:

var list1 = new[] { "Hello", "Bonjour", "Hallo", "Hola" };
var list2 = new[] { "Erwin", "Larry", "Bill", "Steve" };
var list3 = new[] { "!", "..." };
var result = Utils.GetCombinations(list1, list2, list3);
foreach (r in result) {
    Debug.Print(string.Join(" ", r));
}

As with any recursive function, memory usage can be exponential so make sure you know the number of target combinations is reasonable. Speed-wise, parallelizing this function is not worth it as we are just iterating over the elements.

2 commentaires

The easiest way to clone an object (deep copy) in .NET is to use the serialization functions available:

    Public Shared Function CloneObject(ByVal obj As Object) As Object
        If Not obj Is Nothing Then
            Dim bf = New System.Runtime.Serialization.Formatters.Binary.BinaryFormatter()
            Dim fs = New System.IO.MemoryStream()
            bf.Serialize(fs, obj)
            fs.Seek(0, System.IO.SeekOrigin.Begin)
            Dim copy = CType(bf.Deserialize(fs), Object)
            fs.Close()
            Return copy
        Else
            Return Nothing
        End If
    End Function

Though the performance is not very good, for occasional operations it will do the job perfectly. However, I was confronted to the following problem: what if there are events inside the class, to which other objects have subscribed? I found several methods (and functions :-)) on various places over the Internet; they basically were:

• Implement ISerializable yourself (meaning you have to update it each time you modify the class);
• Disconnect from events (retrieved using Reflection), serialize the object, and then reconnect the events (I could not make this working properly);
• Implement a serialization surrogate;
• Implement your events in a separate class that is not serialized;
• Implement your events in a C# base class.

Plenty of potential solutions, but none of them was good enough for me. So I played around with Reflection and found something that nobody else might have done so far. For a cloning interface that does just a shallow copy, like what MemberwiseClone does, but without event, I wrote this:

    Public Function Clone() As Object Implements System.ICloneable.Clone
        Dim cl = New MyClassName(Me)
        'Here we don't capture events, only normal fields, including non public ones (private, protected...)
        Dim FldInfos() As Reflection.FieldInfo = Me.GetType.GetFields(Reflection.BindingFlags.Instance Or Reflection.BindingFlags.Public Or Reflection.BindingFlags.NonPublic)
        For Each FldInfo As Reflection.FieldInfo In FldInfos
            FldInfo.SetValue(cl, FldInfo.GetValue(Me)) 'For serialization purpose we just need not to have events, so no need to perform a deep copy of the fields.
        Next
        Return cl
    End Function

Now if one of your class member is an object with events (or if you want to perform a deep copy), you should call its clone method (to be implemented the same way) when performing the FldInfo.SetValue, like this:

        For Each FldInfo As Reflection.FieldInfo In FldInfos
            If FldInfo.Name <> "MyObjectWithEvents" Then
                FldInfo.SetValue(cl, FldInfo.GetValue(Me)) 'It is not really necessary to clone a possible reference class member here for serialization purpose, we just need not to have events in the clone
            Else
                FldInfo.SetValue(cl, Me.MyObjectWithEvents.Clone())
            End If
        Next

If you have an object that is for example a dictionary of objects with events, you can call this:

        For Each FldInfo As Reflection.FieldInfo In FldInfos
            If FldInfo.Name <> "MyObjectsWithEventsDictionary" Then
                FldInfo.SetValue(cl, MyLib.CloneObject(FldInfo.GetValue(Me))) 
            Else
                FldInfo.SetValue(cl, Me.MyObjectsWithEventsDictionary.ToDictionary(Of String, MyObjectWithEvent)(Function(entry) entry.Key, Function(entry) CType(entry.Value.Clone(), MyObjectWithEvent)))
            End If
        Next

Finally, if you intend to use the Clone interface to serialize objects, you should make sure you don’t include class members marked as NonSerialized():

        For Each FldInfo As Reflection.FieldInfo In FldInfos
            If Not FldInfo.IsNotSerialized Then
                FldInfo.SetValue(cl, FldInfo.GetValue(Me))
            End If
        Next

I hope this will give you an insight to build something more tailored to your needs. There are other optimizations I can already think of, such as implementing a recursive Clone function where you would just put your original object and a virgin instance of it as a reference, and get a perfect serializable deep copy, whatever the class members and sub class members are! This could become a universal Clone method…