[GTK4] Webkit crash on close

[akurtakov]

Start ControlExample and close it after it loads.
It doesn't exit cleanly but with :

SWT call to Webkit timed out after 10000ms. No return value will be provided.
Possible reasons:
1) Problem: Your javascript needs more than 10000ms to execute.
   Solution: Don't run such javascript, it blocks Eclipse's UI. SWT currently allows such code to complete, but this error is thrown 
     and the return value of execute()/evalute() will be false/null.

2) However, if you believe that your application should execute as expected (in under10000 ms),
 then it might be a deadlock in SWT/Browser/webkit2 logic.
 I.e, it might be a bug in SWT (e.g this does not occur on Windows/Cocoa, but occurs on Linux). If you believe it to be a bug in SWT, then
Please report this issue *with steps to reproduce* via:
 https://github.com/eclipse-platform/eclipse.platform.swt/issues/new?assignees=&labels=&projects=&template=bug_report.md&title=
For bug report, please attach this stack trace:
java.lang.Throwable: 
	at org.eclipse.swt.browser.WebKit.getStackTrace(WebKit.java:305)
	at org.eclipse.swt.browser.WebKit.getInternalErrorMsg(WebKit.java:298)
	at org.eclipse.swt.browser.WebKit$Webkit2AsyncToSync.execAsyncAndWaitForReturn(WebKit.java:1321)
	at org.eclipse.swt.browser.WebKit$Webkit2AsyncToSync.runjavascript(WebKit.java:1063)
	at org.eclipse.swt.browser.WebKit$Webkit2AsyncToSync.evaluate(WebKit.java:1033)
	at org.eclipse.swt.browser.WebKit.evaluate(WebKit.java:1348)
	at org.eclipse.swt.browser.WebKit.close(WebKit.java:898)
	at org.eclipse.swt.browser.WebKit.onDispose(WebKit.java:1841)
	at org.eclipse.swt.browser.WebKit.lambda$5(WebKit.java:787)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5889)
        ...

[akurtakov]

A good starting point is probably

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/org/eclipse/swt/browser/WebKit.java

Line 869 in 4a6ab2a

String message1 = Compatibility.getMessage("SWT_OnBeforeUnload_Message1"); // $NON-NLS-1$

[jonahgraham]

One thing I noticed is that the 10s timeout isn't well respected - it could be better respected in a full IDE where there are always lots of events, but because in the loop we do g_main_context_iteration with true it means we rely on some event before checking the timeout condition.

In GTK4GlibFuture I had a similar thing to worry about, which is why it calls g_main_context_iteration with false to not block at this point and then uses Display.sleep with a short scheduled timerExec to wake it up to make sure it doesn't sleep forever.

By applying a similar change I can see the timeout loop respecting the desired timeout:

diff --git a/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/org/eclipse/swt/browser/WebKit.java b/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/org/eclipse/swt/browser/WebKit.java
index 40e39208603..cd4517cab0e 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/org/eclipse/swt/browser/WebKit.java        
+++ b/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/org/eclipse/swt/browser/WebKit.java        
@@ -1326,7 +1329,12 @@ private static class Webkit2AsyncToSync {
                        }
                        else {
                                if (GTK.GTK4) {
-                                       OS.g_main_context_iteration (0, true);
+                                       if (!OS.g_main_context_iteration (0, false)) {
+                                               browser.getDisplay ().timerExec(50, () -> {
+                                                       /* no-op - this exists to prevent sleep from sleeping forever */
+                                               });
+                                               browser.getDisplay ().sleep();
+                                       }
                                } else {
                                        GTK3.gtk_main_iteration_do (true);
                                }

[jonahgraham]

Snippet326 is also a good example of the problem. The close confirm window is not actually shown.

[jonahgraham]

😢 The timeout of execAsyncAndWaitForReturn means if a user in a case like Snippet326 (on GTK3) does not click a button fast enough the browser is closed.

It seems that the issue is much more than just crash on close, but rather in GTK4 I can't get any scripting to work. Snippet161 doesn't work at all and it is a bit easier to debug because it isn't a close/dispose timing.

[jonahgraham]

To me it looks like the webkit integration is quite broken - for example one of the earliest steps is webkit does a callback for decide_policy to webkit_decide_policy. The first call is to webkit_navigation_policy_decision_get_request, which on GTK3 returns a non-zero request. On GTK4 it always returns 0.

(some time later...)

And this is because webkit_navigation_policy_decision_get_request doesn't exist in GTK4 as it was deprecated in GTK3 and all deprecated methods have been removed

(some more time...)

The dynamic load of functions in webkit native means unloadable functions silently fail, if I make this change I can get an error on stderr.

$ git diff "bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/library/webkitgtk.h"
diff --git a/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/library/webkitgtk.h b/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/library/webkitgtk.h
index 9a44f854215..b0f2bd707e3 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/library/webkitgtk.h        
+++ b/bundles/org.eclipse.swt/Eclipse SWT WebKit/gtk/library/webkitgtk.h        
@@ -52,6 +52,7 @@
                } \
                if (handle) { \
                        var = dlsym(handle,     #name); \
+                       if (!var) {     g_critical("SWT webkitgtk: Failed to load webkit function %s", #name); } \
                } \
                CHECK_DLERROR \
                initialized = 1; \

Now that I know at least one of the issues here, I can try to adapt webkit_navigation_policy_decision_get_request -> webkit_navigation_policy_decision_get_navigation_action in GTK4 and find out what else I need to do.