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Refactor SKManagedStream: replace parent/child chain with SKData snapshot for duplicate/fork #3589

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Merged
mattleibow merged 1 commit into from
Mar 30, 2026
Merged

Refactor SKManagedStream: replace parent/child chain with SKData snapshot for duplicate/fork #3589

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99 changes: 30 additions & 69 deletions binding/SkiaSharp/SKManagedStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,10 +11,11 @@ public class SKManagedStream : SKAbstractManagedStream

private bool isAsEnd;
private bool disposeStream;
private bool wasCopied;

private WeakReference parent;
private WeakReference child;
// Lazily-created snapshot for duplicate/fork. Stored in native memory
// via SKData (ref-counted), so multiple duplicates share one native
// byte buffer with no additional managed byte-buffer allocations per duplicate.
private SKData snapshotData;

public SKManagedStream (Stream managedStream)
: this (managedStream, false)
Expand Down Expand Up @@ -56,28 +57,11 @@ protected override void Dispose (bool disposing) =>

protected override void DisposeManaged ()
{
var childStream = child?.Target as SKManagedStream;
var parentStream = parent?.Target as SKManagedStream;

if (childStream != null && parentStream != null) {
// remove this stream from the list by connecting the parent with the child
childStream.parent = parent;
parentStream.child = child;
} else if (childStream != null) {
// transfer ownership to child
childStream.parent = null;
} else if (parentStream != null) {
// transfer ownership back to parent
parentStream.child = null;
parentStream.wasCopied = false;
parentStream.disposeStream = disposeStream;

disposeStream = false;
if (snapshotData != null) {
snapshotData.Dispose ();
snapshotData = null;
}

parent = null;
child = null;

if (disposeStream && stream != null) {
stream.Dispose ();
stream = null;
Expand Down Expand Up @@ -113,15 +97,11 @@ private IntPtr OnReadManagedStream (IntPtr buffer, IntPtr size)

protected internal override IntPtr OnRead (IntPtr buffer, IntPtr size)
{
VerifyOriginal ();

return OnReadManagedStream (buffer, size);
}

protected internal override IntPtr OnPeek (IntPtr buffer, IntPtr size)
{
VerifyOriginal ();

if (!stream.CanSeek) {
return (IntPtr)0;
}
Expand All @@ -133,8 +113,6 @@ protected internal override IntPtr OnPeek (IntPtr buffer, IntPtr size)

protected internal override bool OnIsAtEnd ()
{
VerifyOriginal ();

if (!stream.CanSeek) {
return isAsEnd;
}
Expand All @@ -143,22 +121,16 @@ protected internal override bool OnIsAtEnd ()

protected internal override bool OnHasPosition ()
{
VerifyOriginal ();

return stream.CanSeek;
}

protected internal override bool OnHasLength ()
{
VerifyOriginal ();

return stream.CanSeek;
}

protected internal override bool OnRewind ()
{
VerifyOriginal ();

if (!stream.CanSeek) {
return false;
}
Expand All @@ -168,8 +140,6 @@ protected internal override bool OnRewind ()

protected internal override IntPtr OnGetPosition ()
{
VerifyOriginal ();

if (!stream.CanSeek) {
return (IntPtr)0;
}
Expand All @@ -178,8 +148,6 @@ protected internal override IntPtr OnGetPosition ()

protected internal override IntPtr OnGetLength ()
{
VerifyOriginal ();

if (!stream.CanSeek) {
return (IntPtr)0;
}
Expand All @@ -188,8 +156,6 @@ protected internal override IntPtr OnGetLength ()

protected internal override bool OnSeek (IntPtr position)
{
VerifyOriginal ();

if (!stream.CanSeek) {
return false;
}
Expand All @@ -199,8 +165,6 @@ protected internal override bool OnSeek (IntPtr position)

protected internal override bool OnMove (int offset)
{
VerifyOriginal ();

if (!stream.CanSeek) {
return false;
}
Expand All @@ -210,46 +174,43 @@ protected internal override bool OnMove (int offset)

protected internal override IntPtr OnCreateNew ()
{
VerifyOriginal ();

return IntPtr.Zero;
}

protected internal override IntPtr OnDuplicate ()
private SKData GetOrCreateSnapshot ()
{
VerifyOriginal ();
if (snapshotData != null)
return snapshotData;

if (!stream.CanSeek)
return IntPtr.Zero;

var newStream = new SKManagedStream (stream, disposeStream);
newStream.parent = new WeakReference (this);

wasCopied = true;
disposeStream = false;
child = new WeakReference (newStream);

stream.Position = 0;
return null;

var pos = stream.Position;
try {
stream.Position = 0;
snapshotData = SKData.Create (stream, stream.Length);
} finally {
stream.Position = pos;
}

return newStream.Handle;
return snapshotData;
}

protected internal override IntPtr OnFork ()
protected internal override IntPtr OnDuplicate ()
{
VerifyOriginal ();

var newStream = new SKManagedStream (stream, disposeStream);

wasCopied = true;
disposeStream = false;
var data = GetOrCreateSnapshot ();
if (data == null)
return IntPtr.Zero;

return newStream.Handle;
return SkiaApi.sk_memorystream_new_with_skdata (data.Handle);
}

private void VerifyOriginal ()
protected internal override IntPtr OnFork ()
{
if (wasCopied)
throw new InvalidOperationException ("This stream was duplicated or forked and cannot be read anymore.");
var duplicate = OnDuplicate ();
if (duplicate != IntPtr.Zero)
SkiaApi.sk_stream_seek (duplicate, (IntPtr)stream.Position);
return duplicate;
}
}
}
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