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g_signal_connect returns int while GLib returns gulong, so DropTarget handler ids break at 2^31

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Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
58/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Tranquilla
Stack tecnologico
java
Ambito
desktop

Direzione di ricerca

Read the native declarations in bundles/org.eclipse.swt/Eclipse SWT PI/gtk/org/eclipse/swt/internal/gtk/OS.java alongside the generated stubs in bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/os.c. Then inspect the four handler fields and their connect/disconnect uses in bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/DropTarget.java. Done means the producer declarations and retained handler IDs preserve the GLib return value; build and test the GTK SWT bindings.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

OS.g_signal_connect is declared to return a Java int. GLib's g_signal_connect is a macro over g_signal_connect_data, which returns gulong — 64-bit on LP64. The generated stub casts the result down with (jint), so the C compiler stays quiet and javac never sees the C declaration.

// bundles/org.eclipse.swt/Eclipse SWT PI/gtk/org/eclipse/swt/internal/gtk/OS.java:1357
public static final native int  g_signal_connect(long instance, byte[] detailed_signal, long proc, long data);

// OS.java:1402 — this side was widened by #462 / 417af5e1
public static final native void g_signal_handler_disconnect(long instance, long handler_id);

/* bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/os.c */
rc = (jint)g_signal_connect((gpointer)arg0, (const gchar *)lparg1, ...);

// bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/DropTarget.java
:103    int drag_motion_handler;
:206    drag_motion_handler = OS.g_signal_connect(control.handle, OS.drag_motion, ...);
:669    OS.g_signal_handler_disconnect(control.handle, drag_motion_handler);
What it can cause

#462 widened g_signal_handler_disconnect, but the id is truncated by the producer before it ever reaches the consumer, and DropTarget holds it in an int field. Java's int → long widening is a sign extension (JLS 5.1.2), so widening the parameter could not recover the bits:

handler id what GLib receives on disconnect effect
< 2^31 the same id fine — which is why this has not been seen
2^31 … 2^32 0xFFFFFFFF80000000-style an id GLib never issued; the handler is not disconnected and keeps running against a disposed DropTarget
> 2^32 a different, small id (2^32 + 5 → 5) may name a live handler belonging to something else

The threshold usually quoted for this is 4G, because that is where a gulong stops fitting in 32 bits. Java's int is signed and the conversion back is a sign extension, so the first id that fails to round-trip is 2 147 483 648, half of that. Against the rate measured in 417af5e1 ("counter jumps by ~20k" per window open and close), that halves the time to failure.

No observed failure — nothing here was built or run, and no id above 2^31 was witnessed. LP64 only; under LLP64 gulong is 32-bit and none of this applies.

Fix

Declare long on the producer — g_signal_connect, and the same for g_signal_connect_closure (OS.java:1364) and g_signal_connect_closure_by_id (:1372), which have the identical mismatch but whose returns no caller currently keeps — and widen the four DropTarget fields at :103-106 with them. The consumer side is already correct.

How this was found

By a research tool that compares each Java native declaration against the C declaration of the function its generated stub actually calls. The 2^31 threshold was then derived as arithmetic. Every line quoted above was re-read on master on 2026-08-16.

Edited 2026-08-16: shortened. The claim, the evidence and the line numbers are unchanged.

Lingua principale
Java
Stelle
202
Fork
206
Merge medio
16h 56m
PR unite (30g)
110

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