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[runtime] Reduce registered peer storage allocations #12657

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Merged
simonrozsival merged 1 commit into from
Sep 3, 2026
+734 −42
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[runtime] Reduce registered peer storage allocations #12657

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182 changes: 140 additions & 42 deletions src/Mono.Android/Microsoft.Android.Runtime/JavaMarshalRegisteredPeers.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Java;
using System.Threading;
using Android.Runtime;
using Java.Interop;

Expand All @@ -31,8 +32,9 @@ namespace Microsoft.Android.Runtime;
/// </remarks>
static class JavaMarshalRegisteredPeers
{
static readonly Dictionary<int, List<ReferenceTrackingHandle>> RegisteredInstances = new ();
static readonly Dictionary<int, RegisteredPeerBucket> RegisteredInstances = new ();
static readonly ConcurrentQueue<IntPtr> CollectedContexts = new ();
static readonly Lock s_instancesLock = new ();

static readonly object initializeLock = new ();
static bool initialized;
Expand Down Expand Up @@ -65,7 +67,7 @@ public static void CollectPeers ()
Debug.Assert (contextPtr != IntPtr.Zero, "CollectedContexts should not contain null pointers.");
HandleContext* context = (HandleContext*)contextPtr;

lock (RegisteredInstances) {
lock (s_instancesLock) {
Remove (context);
}

Expand All @@ -75,18 +77,19 @@ public static void CollectPeers ()
void Remove (HandleContext* context)
{
int key = context->PeerIdentityHashCode;
if (!RegisteredInstances.TryGetValue (key, out List<ReferenceTrackingHandle>? peers))
if (!RegisteredInstances.TryGetValue (key, out RegisteredPeerBucket peers))
return;

for (int i = peers.Count - 1; i >= 0; i--) {
var peer = peers [i];
if (peer.BelongsToContext (context)) {
if (peers [i].BelongsToContext (context)) {
peers.RemoveAt (i);
}
}

if (peers.Count == 0) {
RegisteredInstances.Remove (key);
} else {
RegisteredInstances [key] = peers;
}
}
}
Expand All @@ -106,45 +109,71 @@ public static void AddPeer (IJavaPeerable value)
JniObjectReference.Dispose (ref r, JniObjectReferenceOptions.CopyAndDispose);
}
int key = value.JniIdentityHashCode;
lock (RegisteredInstances) {
List<ReferenceTrackingHandle>? peers;
if (!RegisteredInstances.TryGetValue (key, out peers)) {
peers = [new ReferenceTrackingHandle (value)];
RegisteredInstances.Add (key, peers);
lock (s_instancesLock) {
if (!RegisteredInstances.TryGetValue (key, out RegisteredPeerBucket peers)) {
RegisteredInstances.Add (key, new RegisteredPeerBucket (new ReferenceTrackingHandle (value)));
return;
}

for (int i = peers.Count - 1; i >= 0; i--) {
ReferenceTrackingHandle peer = peers [i];
if (peer.Target is not IJavaPeerable target)
continue;
if (!JniEnvironment.Types.IsSameObject (target.PeerReference, value.PeerReference))
continue;
// JNIEnv.NewObject/JNIEnv.CreateInstance() compatibility.
// When two MCW's are created for one Java instance [0],
// we want the 2nd MCW to replace the 1st, as the 2nd is
// the one the dev created; the 1st is an implicit intermediary.
//
// Meanwhile, a new "replaceable" instance should *not* replace an
// existing "replaceable" instance; see dotnet/android#9862.
//
// [0]: If Java ctor invokes overridden virtual method, we'll
// transition into managed code w/o a registered instance, and
// thus will create an "intermediary" via
// (IntPtr, JniHandleOwnership) .ctor.
if (target.JniManagedPeerState.HasFlag (JniManagedPeerStates.Replaceable) &&
!value.JniManagedPeerState.HasFlag (JniManagedPeerStates.Replaceable)) {
peer.Dispose ();
peers [i] = new ReferenceTrackingHandle (value);
} else if (JniEnvironment.Runtime.ObjectReferenceManager.LogGlobalReferenceMessages) {
WarnNotReplacing (key, value, target);
var result = ReconcilePeer (peers [i], value, key, out ReferenceTrackingHandle replacement);
if (result == PeerReconciliationResult.Replace) {
peers [i] = replacement;
RegisteredInstances [key] = peers;
return;
}
GC.KeepAlive (target);
return;
if (result == PeerReconciliationResult.Keep)
return;
}

peers.Add (new ReferenceTrackingHandle (value));
RegisteredInstances [key] = peers;
}
}

enum PeerReconciliationResult
{
NoMatch,
Keep,
Replace,
}

static PeerReconciliationResult ReconcilePeer (
ReferenceTrackingHandle registered,
IJavaPeerable value,
int key,
out ReferenceTrackingHandle replacement)
{
replacement = default;
if (registered.Target is not IJavaPeerable target)
return PeerReconciliationResult.NoMatch;
if (!JniEnvironment.Types.IsSameObject (target.PeerReference, value.PeerReference))
return PeerReconciliationResult.NoMatch;

// JNIEnv.NewObject/JNIEnv.CreateInstance() compatibility.
// When two MCW's are created for one Java instance [0],
// we want the 2nd MCW to replace the 1st, as the 2nd is
// the one the dev created; the 1st is an implicit intermediary.
//
// Meanwhile, a new "replaceable" instance should *not* replace an
// existing "replaceable" instance; see dotnet/android#9862.
//
// [0]: If Java ctor invokes overridden virtual method, we'll
// transition into managed code w/o a registered instance, and
// thus will create an "intermediary" via
// (IntPtr, JniHandleOwnership) .ctor.
if (target.JniManagedPeerState.HasFlag (JniManagedPeerStates.Replaceable) &&
!value.JniManagedPeerState.HasFlag (JniManagedPeerStates.Replaceable)) {
registered.Dispose ();
replacement = new ReferenceTrackingHandle (value);
GC.KeepAlive (target);
return PeerReconciliationResult.Replace;
}

if (JniEnvironment.Runtime.ObjectReferenceManager.LogGlobalReferenceMessages)
WarnNotReplacing (key, value, target);
GC.KeepAlive (target);
return PeerReconciliationResult.Keep;
}

static void WarnNotReplacing (int key, IJavaPeerable ignoreValue, IJavaPeerable keepValue)
Expand All @@ -170,8 +199,8 @@ static void WarnNotReplacing (int key, IJavaPeerable ignoreValue, IJavaPeerable

int key = JniEnvironment.References.GetIdentityHashCode (reference);

lock (RegisteredInstances) {
if (!RegisteredInstances.TryGetValue (key, out List<ReferenceTrackingHandle>? peers))
lock (s_instancesLock) {
if (!RegisteredInstances.TryGetValue (key, out RegisteredPeerBucket peers))
return null;

for (int i = peers.Count - 1; i >= 0; i--) {
Expand All @@ -196,9 +225,9 @@ public static void RemovePeer (IJavaPeerable value)
if (value == null)
throw new ArgumentNullException (nameof (value));

lock (RegisteredInstances) {
lock (s_instancesLock) {
int key = value.JniIdentityHashCode;
if (!RegisteredInstances.TryGetValue (key, out List<ReferenceTrackingHandle>? peers))
if (!RegisteredInstances.TryGetValue (key, out RegisteredPeerBucket peers))
return;

for (int i = peers.Count - 1; i >= 0; i--) {
Expand All @@ -212,6 +241,8 @@ public static void RemovePeer (IJavaPeerable value)
}
if (peers.Count == 0)
RegisteredInstances.Remove (key);
else
RegisteredInstances [key] = peers;
}
}

Expand Down Expand Up @@ -255,10 +286,11 @@ public static List<JniSurfacedPeerInfo> GetSurfacedPeers ()
// Remove any collected contexts before iterating over all the registered instances
CollectPeers ();

lock (RegisteredInstances) {
lock (s_instancesLock) {
var peers = new List<JniSurfacedPeerInfo> (RegisteredInstances.Count);
foreach (var (identityHashCode, referenceTrackingHandles) in RegisteredInstances) {
foreach (var peer in referenceTrackingHandles) {
foreach (var (identityHashCode, registered) in RegisteredInstances) {
for (int i = 0; i < registered.Count; i++) {
var peer = registered [i];
if (peer.Target is IJavaPeerable target) {
peers.Add (new JniSurfacedPeerInfo (identityHashCode, new WeakReference<IJavaPeerable> (target)));
}
Expand All @@ -268,6 +300,70 @@ public static List<JniSurfacedPeerInfo> GetSurfacedPeers ()
}
}

struct RegisteredPeerBucket
{
ReferenceTrackingHandle _first;
List<ReferenceTrackingHandle>? _rest;

public RegisteredPeerBucket (ReferenceTrackingHandle first)
{
_first = first;
_rest = null;
}

public int Count => (_first.IsValid ? 1 : 0) + (_rest?.Count ?? 0);

public ReferenceTrackingHandle this [int index] {
get {
if (index == 0 && _first.IsValid)
return _first;

var rest = _rest;
if (rest == null)
throw new ArgumentOutOfRangeException (nameof (index));
return rest [index - 1];
}
set {
if (index == 0 && _first.IsValid) {
_first = value;
return;
}

var rest = _rest;
if (rest == null)
throw new ArgumentOutOfRangeException (nameof (index));
rest [index - 1] = value;
}
}

public void Add (ReferenceTrackingHandle peer)
{
if (!_first.IsValid) {
_first = peer;
return;
}

_rest ??= [];
_rest.Add (peer);
}

public void RemoveAt (int index)
{
if (index == 0) {
_first = default;
if (_rest?.Count > 0) {
_first = _rest [0];
_rest.RemoveAt (0);
}
} else {
_rest?.RemoveAt (index - 1);
}

if (_rest?.Count == 0)
_rest = null;
}
}

unsafe struct ReferenceTrackingHandle : IDisposable
{
WeakReference<IJavaPeerable?> _weakReference;
Expand All @@ -285,6 +381,8 @@ public ReferenceTrackingHandle (IJavaPeerable peer)
public IJavaPeerable? Target
=> _weakReference.TryGetTarget (out var target) ? target : null;

public bool IsValid => _context != null;

public void Dispose ()
{
if (_context == null)
Expand Down
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