[swift-users] Making a copy of an UnsafePointer<UInt8>

[Rick Mann]

> On Nov 15, 2017, at 00:48 , Quinn The Eskimo! via swift-users <swift-users at swift.org> wrote:
> 
> 
> On 15 Nov 2017, at 04:16, Rick Mann via swift-users <swift-users at swift.org> wrote:
> 
>> Is UnsafeMutablePointer<> not memory managed?
> 
> It is not.  Specifically, the code you posted creates a copy of the data and then never destroys it.

Hmm. So it should leak, not crash. I wonder what I'm doing wrong.

> If I were in your shoes I’d construct a `Data` value from the unsafe pointer and then pass that around.
> 
> let source = Data(bytes: inSourceBuffer, count: inSourceBufferLength)
> self.queue.async {
>    let size = source.count
>    source.withUnsafeBytes { (p: UnsafePointer<UInt8>) in
>        self.foo(data: p, length: size)
>    }
> }
> 
> The main drawback to this is that you have to jump through the hoops to access the data unsafely.  It might be easier to recast your consumer (the `foo(…)` method) in terms of `Data`.  That’s what I generally do when I work with foreign APIs like this, that is, keep the data in ‘Swift space’ and only deal with foreign types at the boundaries.
> 
> Whether that makes sense here really depends on the specifics of your program.  For example, if your program has lots of this boundary code, it might be nicer to just stick with the foreign type.  Or build a specific wrapper that makes it easier to do this conversion.

Thanks. I have to call this code from Objective-C, passing a pointer and length (which is how I get the raw data). I could create CGImages from that, and I might, since eventually the consumer will be implemented in Metal 2. But right now, I just have to get back to the raw data to do the processing, so it seemed like extra work to create a CGImage.


-- 
Rick Mann
rmann at latencyzero.com