[DllImportGenerator] Initialize by-value out array to default #61431
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
jkoritzinsky
approved these changes
Nov 10, 2021
AaronRobinsonMSFT
approved these changes
Nov 10, 2021
| @@ -71,6 +71,8 @@ Only single-dimensional arrays are supported for source generated marshalling. | |||
|
|
|||
| In the source-generated marshalling, arrays will be allocated on the stack (instead of through [`AllocCoTaskMem`](https://docs.microsoft.com/dotnet/api/system.runtime.interopservices.marshal.alloccotaskmem)) if they are passed by value or by read-only reference if they contain at most 256 bytes of data. The built-in system does not support this optimization for arrays. | |||
|
|
|||
| In the built-in system, marshalling a `char` array by value with `CharSet.Unicode` would default to also marshalling data out. In the source-generated marshalling, the `char` array must be marked with the `[Out]` attribute for data to be marshalled out by value. | |||
There was a problem hiding this comment.
This is due to the fact that a char array with CharSet.Unicode used to be pinnacle as char is blittable with CharSet.Unicode
There was a problem hiding this comment.
Yeah, I figured that was it once I saw the behaviour, but it was not something I realized immediately 😕
elinor-fung
added
area-System.Runtime.InteropServices
source-generator
This was referenced Nov 29, 2021
ghost
locked as resolved and limited conversation to collaborators
Sign up for free
to subscribe to this conversation on GitHub.
Already have an account?
Sign in.
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
When marshalling an array out by value, we were leaving the native storage uninitialized. This clears it out, so that we don't end up with whatever garbage was there in the array (matches built-in system behaviour).
This is the reason behind the failures in #61389.
@AaronRobinsonMSFT @jkoritzinsky