fix(ab): destroy the native libplctag tag a failed initialisation leaves behind (T21 press pass 1 crash)

The T21 press pass 1 test host died at exit with "A callback was made on a garbage collected delegate of type ...plctag+callback_func_ex::Invoke". The cause is in libplctag.NET 1.5.2. When a tag's create fails, for example with NotFound, InitializeAsync throws with the callback still registered. Dispose() destroys a tag only if it is initialised, so the native tag outlives its wrapper. The GC then frees the delegate, and libplctag's atexit plc_tag_shutdown raises DESTROYED into it. Reproduced against ab_server: the production LibplctagTagRuntime with a NotFound tag exits 134 with that exact message, and exits 0 with this fix. A timed-out create unregisters its callback but never destroys the handle either, so that native tag keeps reconnecting for the life of the process. The fix adds LibplctagOrphanRelease (AbCip and AbLegacy). After a failed initialise/read/write that leaves the tag uninitialised, it reads the handle through the pinned wrapper's private fields, unregisters the callback and destroys the tag. If those fields cannot be read, it roots the tag for the life of the process instead. It is applied in both tag runtimes, the symbol-listing reader and the template reader. GetStatus keeps the status the tag held before it was destroyed. Pins: offline refused-connection tests in AbCip.Tests and AbLegacy.Tests, a live NotFound test on ab_server, and a reflection-shape pin. All go red with the release disabled. The differential harness also asserts that no orphan had to be rooted. Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
2026-10-07 19:49:03 -04:00
parent c306c6f674
commit 6cd6876229
10 changed files with 462 additions and 12 deletions
@@ -138,6 +138,21 @@ public sealed class TransportDifferentialTests(DifferentialRunFixture fixture)
        r.ConnectionsBeforeNative.Value.ShouldBeLessThanOrEqualTo(r.ConnectionsBaseline.Value);
    }

+    /// <summary>
+    ///     T21 press pass 1 ended in "A callback was made on a garbage collected delegate": libplctag tags whose
+    ///     initialisation failed (NotFound tags, refused latency setups) were left native-side with a live callback.
+    ///     Every libplctag tag this harness creates goes through the driver's adapters, which now destroy such a tag
+    ///     (<see cref="LibplctagOrphanRelease"/>); this pins that none had to fall back to being rooted instead.
+    /// </summary>
+    [Fact]
+    public async Task No_failed_libplctag_tag_is_left_with_a_live_native_callback()
+    {
+        await RunOrSkipAsync();
+        Log($"libplctag orphans destroyed so far: {LibplctagOrphanRelease.Released}; rooted (unreleasable): {LibplctagOrphanRelease.RootedCount}.");
+        LibplctagOrphanRelease.CanReadHandles.ShouldBeTrue();
+        LibplctagOrphanRelease.RootedCount.ShouldBe(0);
+    }
+
    [Fact]
    public async Task The_native_side_makes_exactly_one_forward_open_over_the_whole_run()
    {
@@ -0,0 +1,43 @@
+using libplctag.NativeImport;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests;
+
+/// <summary>
+///     T21 press pass 1 crash, the variant that killed the test host: a tag the controller does not have. libplctag
+///     raises <c>Created</c> with NotFound, so libplctag.NET 1.5.2 throws WITHOUT unregistering its callback, and its
+///     <c>Dispose()</c> skips the uninitialised tag. Before the fix the native tag survived with a live callback into a
+///     delegate the GC was free to collect; libplctag's <c>atexit</c> shutdown then raised DESTROYED into it ("A callback
+///     was made on a garbage collected delegate"). This pins that the native tag is destroyed instead.
+/// </summary>
+[Trait("Category", "Integration")]
+[Trait("Requires", "AbServer")]
+public sealed class LibplctagOrphanReleaseLiveTests
+{
+    [AbServerFact]
+    public async Task A_tag_the_controller_lacks_leaves_no_native_tag_behind()
+    {
+        var fixture = new AbServerFixture();
+        var rt = new LibplctagTagRuntime(new AbCipTagCreateParams(
+            Gateway: fixture.Host, Port: fixture.Port, CipPath: "1,0", LibplctagPlcAttribute: "controllogix",
+            TagName: "T21_NoSuchTag", Timeout: TimeSpan.FromSeconds(5)));
+        try
+        {
+            var ex = await Should.ThrowAsync<AbTransportException>(() => rt.InitializeAsync(CancellationToken.None));
+            ex.Status.ShouldBe(AbStatus.NotFound);
+            rt.GetStatus().ShouldBe((int)AbStatus.NotFound);
+
+            var handle = rt.NativeHandle;
+            handle.ShouldBeGreaterThan(0);
+            var exists = plctag.plc_tag_lock(handle) == 0;
+            if (exists) plctag.plc_tag_unlock(handle);
+            exists.ShouldBeFalse("a NotFound tag must not survive with its callback registered");
+        }
+        finally
+        {
+            rt.Dispose();
+        }
+    }
+}