C#•2y ago

✅ [[QUESTION]] HOW TO CALCULATE THE Rent(int) property for System.Buffers.ArrayPool<byte> ?

Hey, I have a question about System.Buffers.ArrayPool<byte> I tried to read the document many times but I didn't get it. what is the Rent(int) property of System.Buffers.ArrayPool<byte> ? How do I know how many bytes I need for the buffer? If I need a string of 5 characters, Rent(5) is enough ... I know that and it works. but what if I need : 1 - String(5 character) 2 - bool 3 - Int(1 digit ) (1-5) 4 - Int(1 digit ) (1-5) 5 - Int(1 digit ) (1-5) 6 - Int(1 digit ) (1-5) How do I calculate the Rent value I need?

54 Replies

ero•2y ago

5 bytes is not enough for a string of 5 characters sizeof(bool), sizeof(int) for the others But this seems like an incorrect use of ArrayPool It'd be better if you just told is what you're doing

zylogOP•2y ago

@Ero here is an example, if I used Rent(5) with just name it works , if I added everything else it raises an error

ero•2y ago

That's hardly an examplr

Unknown User•2y ago

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MODiX•2y ago

tebeco#0205

REPL Result: Success

sizeof(char)

sizeof(char)

Result: int

Compile: 302.978ms | Execution: 22.345ms | React with ❌ to remove this embed.

Unknown User•2y ago

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gerard•2y ago

The parameter of Rent(int) is the minimal size that the array should have. So note that the array can be larger than requested

How do I calculate the Rent value I need?

By adding the lengths together.

5 bytes is not enough for a string of 5 characters

What they are trying to say that string.Length doesn't equal to the amount of bytes it requires. For example, a string with an emoji ("🤔") is 4 bytes. You can get the amount of bytes you need with:

Encoding.UTF8.GetByteCount("🤔")

Encoding.UTF8.GetByteCount("🤔")

That said, you can add everything together to see how much bytes you need.

var size = Encoding.UTF8.GetByteCount(input) + sizeof(bool) + sizeof(int) * 4; // or sizeof(byte), since they are 1-5

var size = Encoding.UTF8.GetByteCount(input) + sizeof(bool) + sizeof(int) * 4; // or sizeof(byte), since they are 1-5

You don't need to worry about the + and *, C# will optimize these in release mode to 16.

zylogOP•2y ago

sorry I accidentally deleted it -.-

public public ArrayPool<byte> _sendBuffers;
public string someName;
public bool someBool;
public int int1;
public int int2;
public int int3;
public int int4;

int pos = 0;
byte[] sendBuffer = _sendBuffers.Rent(50);

sendBuffer.WriteString(ref pos, someName);            
sendBuffer.WriteBool(ref pos, someBool);
sendBuffer.WriteInt(ref pos, int1);
sendBuffer.WriteInt(ref pos, int2);
sendBuffer.WriteInt(ref pos, int3);
sendBuffer.WriteInt(ref pos, int4);
Program.comms.ServerSend(clientId, 0, new ArraySegment<byte>(sendBuffer, 0, pos));

public public ArrayPool<byte> _sendBuffers;
public string someName;
public bool someBool;
public int int1;
public int int2;
public int int3;
public int int4;

int pos = 0;
byte[] sendBuffer = _sendBuffers.Rent(50);

sendBuffer.WriteString(ref pos, someName);            
sendBuffer.WriteBool(ref pos, someBool);
sendBuffer.WriteInt(ref pos, int1);
sendBuffer.WriteInt(ref pos, int2);
sendBuffer.WriteInt(ref pos, int3);
sendBuffer.WriteInt(ref pos, int4);
Program.comms.ServerSend(clientId, 0, new ArraySegment<byte>(sendBuffer, 0, pos));

@Ero @TeBeConsulting here is an Example that is the problem

The parameter of Rent(int) is the minimal size that the array should have. So note that the array can be larger than requested

If that is the case, then why it doesn't work when I add lower value than 20 ??

gerard•2y ago

What's the problem with that? What do you mean with "it doesn't work"?

zylogOP•2y ago

it raises and error in the Try and catch method

Unknown User•2y ago

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zylogOP•2y ago

the program shuts down

Unknown User•2y ago

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zylogOP•2y ago

doesnt finish the request

Unknown User•2y ago

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zylogOP•2y ago

@TeBeConsulting Where ? if I add more buffer , it works , minimum 18 I think

Unknown User•2y ago

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zylogOP•2y ago

its being incrementing inside

Unknown User•2y ago

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gerard•2y ago

Oh you mean that the array isn't large enough for the data. That's what you mean with Rent(20) doesn't work, which makes sense. Again, you can calculate the length you need to rent. What's also common is that when the array isn't large enough, you return the array and make a larger one. But that's on you how you want to solve that.

zylogOP•2y ago

@TeBeConsulting its very hard to share and run the code, because its a large communication between clients and server that goes back and furth multiple time from the same request but it breaks at that point

Unknown User•2y ago

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zylogOP•2y ago

but arent we defining the Minimum length not the maximum? why do I need to increase the minimum length ?

gerard•2y ago

Well yes, it's a minimum length. But if you don't know what the string holds and you're guessing the length then you're asking for problems.

zylogOP•2y ago

true , I understand I cant share the entire server just to debug that, no one has the time , Im just fishing for what could be the common causes

gerard•2y ago

I don't understand what the problem is, you don't want to calculate the minimal length and want to put a constant value in? What's wrong with pre-calculating the array length you want to rent?

zylogOP•2y ago

should I not include the rent part of the code and let the program ?

Unknown User•2y ago

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MODiX•2y ago

tebeco#0205

REPL Result: Success

sizeof(char)

sizeof(char)

Result: int

Compile: 278.301ms | Execution: 21.153ms | React with ❌ to remove this embed.

Unknown User•2y ago

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gerard•2y ago

True, we don't know what WriteString does. It can write UTF-16 bytes (then it's 6 bytes) or UTF-8 (then it's 3 bytes).

Unknown User•2y ago

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zylogOP•2y ago

@gerard im just updating a program that isnt mine the original code had only string and it was Rent(5) == > that was working very well. but not I've added a bool and 4 other Integers ( to be converted to Enum on the client side later ) I couldnt leave Rent(5) as its because of the error , and when I raise it above 18 (aka: Rent(18) ) it works what could be the issue ?

Unknown User•2y ago

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zylogOP•2y ago

there is no repro, its private contract.

Unknown User•2y ago

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zylogOP•2y ago

fair

Unknown User•2y ago

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zylogOP•2y ago

I think adding a bigger minimum value for Rent() should be enough hint to the problem , maybe there is buffer hanging somewhere that hasnt returned yet ?

gerard•2y ago

No clue, without code it's hard to say if the buffer hasn't returned. But that has nothing to do with the minimal length

Unknown User•2y ago

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gerard•2y ago

If your array isn't large enough for the amount of data you're trying to send, it makes sense it throws.

Unknown User•2y ago

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zylogOP•2y ago

oh , but I thought we are defining the minimum not the maximum value of the array, isnt that right ?

gerard•2y ago

An array is a fixed length. I don't think you understand how the array pool works. .Rent(16) will always be a length of 16 or higher. So for example: byte[16] but it can also return byte[32]

zylogOP•2y ago

maybe that is the issue, the current array that im renting from isnt big enough maybe.

gerard•2y ago

Because if the array pool would return the exact length for every array (e.g. 16, 17, 18), the pool would have to create a lot of arrays that matches that length. So it makes sense it gets something that's minimal that amount you're trying to get.

zylogOP•2y ago

I think I get what u meant. I dont wanna bother u any longer , let me do few debugs and try to make sense of what exactly in the buffer and how long is it and I'd return with an update if i figured it out , but you said kinda make sense but also I feel I need to learn how pool array works in depth @gerard Thanks a lot 🙂 @TeBeConsulting Thanks 🙂 I'll return with an update if I got anything useful oh shit I got it ... Rent() has fixed values , and @TeBeConsulting @gerard was right , its just not large enough for the data I was trying to send but the fixed value part was the surprise for me Example Rent(1), Rent(2), Rent(3), Rent(4), Rent(5), ... Rent(16) all have the same array length (16) and Rent(17), Rent(18), Rent(19), Rent(20), Rent(21), ... Rent(32) all have the same array length (32) and Rent(33), Rent(34), Rent(35), Rent(36), Rent(37), ... Rent(64) all have the same array length (64)

Unknown User•2y ago

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zylogOP•2y ago

yeah , so my data needed 30+ so I lied in the middle Rent(32) so basically, Rent(17-32) are the same .. they should have made it that simple

gerard•2y ago

It doesn't have to tho. If you rent a lot of .Rent(128) and return them to the pool, it's possible that .Rent(32) will now also return a byte[128] (since all of the 32-length arrays have been disposed). There is a limit on how much the pool holds.

zylogOP•2y ago

I see, so we got to be aware of the length of the array with send and make sure that we return it otherwise, we would have some performance impact. yeah that make sense now :D, thanks a lot 🙂 but I think they should have made it more like Rent(16) , Rent(32) , Rent(64) ... etc instead of Rent(int) >>> this sends the wrong message that we could send an array of length 14 or 15 which is not true

gerard•2y ago

That's why the parameter name is called "minimumLength". Not "length" 😜

zylogOP•2y ago

true 😄

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✅ [[QUESTION]] HOW TO CALCULATE THE Rent(int) property for System.Buffers.ArrayPool<byte> ?