[Java.Interop] Prevent premature collection w/ JniInstance* #768
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jonpryor
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radekdoulik
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src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods_Invoke.cs
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Context: dotnet/android@e88cfbc While writing the commit message for dotnet/android@e88cfbcf, it occurred to me that the same fundamental scenario of: CallIntoJava (new JavaLangObjectSubclass ().Handle); // GC collects instance after `.Handle`, before `CallIntoJava()` could apply to `JniPeerMembers.JniInstanceMethods.Invoke*()` invocations: JniArgumentValue* __args = …; _members.InstanceMethods.InvokeVirtualObjectMethod (__id, this, __args); // What prevents `this` from being collected "too soon"? Address this: update `JniPeerMembers.JniInstanceMethods.Invoke*()` so that there is a `GC.KeepAlive(self)` after accessing `self.PeerReference`. This will ensure that `self` isn't collected "during" `JniEnvironment.InstanceMethods.Call*Method()` invocations. Likewise update `JniPeerMembers.JniInstanceFields.Get*Value()` and `JniPeerMembers.JniInstanceFields.Set*Value()` so that there is a `GC.KeepAlive(self)` after the `JniEnvironment.InstanceFields.*` invocation.
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LGTM.
The only thing I was wondering about is
<#= returnType.ReturnType != "void" ? "var r = " : "" #>JniEnvironment.InstanceMethods.CallNonvirtual<#= returnType.JniCallType #>Method (self.PeerReference, j.JniPeerType.PeerReference, n, parameters); line. If I understand it correctly, the j.JniPeerType should be kept alive by self being alive. So that should be fine.
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Context: dotnet/android@e88cfbc While writing the commit message for xamarin/xamarin-android/@e88cfbcf, it occurred to me that the same fundamental scenario of: CallIntoJava (new JavaLangObjectSubclass ().Handle); // GC collects instance after `.Handle`, before `CallIntoJava()` could apply to `JniPeerMembers.JniInstanceMethods.Invoke*()` invocations: JniArgumentValue* __args = …; _members.InstanceMethods.InvokeVirtualObjectMethod (__id, this, __args); // What prevents `this` from being collected "too soon"? Address this: update `JniPeerMembers.JniInstanceMethods.Invoke*()` so that there is a `GC.KeepAlive(self)` after accessing `self.PeerReference`. This will ensure that `self` isn't collected "during" `JniEnvironment.InstanceMethods.Call*Method()` invocations. Likewise update `JniPeerMembers.JniInstanceFields.Get*Value()` and `JniPeerMembers.JniInstanceFields.Set*Value()` so that there is a `GC.KeepAlive(self)` after the `JniEnvironment.InstanceFields.*` invocation.
jonpryor
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Jan 5, 2021
Context: dotnet/android@e88cfbc While writing the commit message for xamarin/xamarin-android/@e88cfbcf, it occurred to me that the same fundamental scenario of: CallIntoJava (new JavaLangObjectSubclass ().Handle); // GC collects instance after `.Handle`, before `CallIntoJava()` could apply to `JniPeerMembers.JniInstanceMethods.Invoke*()` invocations: JniArgumentValue* __args = …; _members.InstanceMethods.InvokeVirtualObjectMethod (__id, this, __args); // What prevents `this` from being collected "too soon"? Address this: update `JniPeerMembers.JniInstanceMethods.Invoke*()` so that there is a `GC.KeepAlive(self)` after accessing `self.PeerReference`. This will ensure that `self` isn't collected "during" `JniEnvironment.InstanceMethods.Call*Method()` invocations. Likewise update `JniPeerMembers.JniInstanceFields.Get*Value()` and `JniPeerMembers.JniInstanceFields.Set*Value()` so that there is a `GC.KeepAlive(self)` after the `JniEnvironment.InstanceFields.*` invocation.
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Context: dotnet/android@e88cfbc
While writing the commit message for xamarin/xamarin-android/@e88cfbcf,
it occurred to me that the same fundamental scenario of:
could apply to
JniPeerMembers.JniInstanceMethods.Invoke*()invocations:
Address this: update
JniPeerMembers.JniInstanceMethods.Invoke*()so that there is a
GC.KeepAlive(self)after accessingself.PeerReference. This will ensure thatselfisn't collected"during"
JniEnvironment.InstanceMethods.Call*Method()invocations.Likewise update
JniPeerMembers.JniInstanceFields.Get*Value()andJniPeerMembers.JniInstanceFields.Set*Value()so that there is aGC.KeepAlive(self)after theJniEnvironment.InstanceFields.*invocation.