tor-browser

commit c141abb081a2a3d2ef3b4aeb70b9476a6b84677e
parent 35055c39b060b8014a4dd74b2e97acdf2abd46ac
Author: Matthew Gaudet <mgaudet@mozilla.com>
Date:   Mon, 20 Oct 2025 17:56:01 +0000

Bug 1990930 - Clarify and validate OOM (crashing) in Gecko use of JS microtask queue r=smaug,arai,dom-worker-reviewers,edenchuang

Differential Revision: https://phabricator.services.mozilla.com/D268619

Diffstat:
M
dom/workers/RuntimeService.cpp
 | 
8
++++----
M
js/public/friend/MicroTask.h
 | 
4
+++-
M
xpcom/base/CycleCollectedJSContext.cpp
 | 
7
+++----

3 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/dom/workers/RuntimeService.cpp b/dom/workers/RuntimeService.cpp
@@ -1015,16 +1015,16 @@ class WorkerJSContext final : public mozilla::CycleCollectedJSContext {
       if (IsWorkerGlobal(global) || IsShadowRealmGlobal(global)) {
         if (!EnqueueMicroTask(cx, runnable.forget())) {
           // This should never fail, but if it does, we have no choice but to
-          // crash.
-          MOZ_CRASH("Failed to enqueue micro task from worker.");
+          // crash. This is always an OOM.
+          NS_ABORT_OOM(0);
         }
       } else {
         MOZ_ASSERT(IsWorkerDebuggerGlobal(global) ||
                    IsWorkerDebuggerSandbox(global));
         if (!EnqueueDebugMicroTask(cx, runnable.forget())) {
           // This should never fail, but if it does, we have no choice but to
-          // crash.
-          MOZ_CRASH("Failed to enqueue debugger micro task from worker.");
+          // crash. This is always an OOM.
+          NS_ABORT_OOM(0);
         }
       }
     } else {
diff --git a/js/public/friend/MicroTask.h b/js/public/friend/MicroTask.h
@@ -66,7 +66,7 @@ JS_PUBLIC_API bool IsJSMicroTask(const JS::Value& hv);
 // Run a MicroTask that is known to be a JS MicroTask. This will crash
 // if provided an invalid task kind.
 //
-// This will return true except on OOM.
+// This will return false if an exception is thrown while processing.
 JS_PUBLIC_API bool RunJSMicroTask(JSContext* cx, Handle<MicroTask> entry);
 
 // Queue Management. This is done per-JSContext.
@@ -81,6 +81,8 @@ JS_PUBLIC_API bool RunJSMicroTask(JSContext* cx, Handle<MicroTask> entry);
 // In general, we highly recommend that most embeddings use only the regular
 // microtask queue. The debugger microtask queue mostly exists to support
 // patterns used by Gecko.
+//
+// These methods only fail for OOM.
 JS_PUBLIC_API bool EnqueueMicroTask(JSContext* cx, const MicroTask& entry);
 JS_PUBLIC_API bool EnqueueDebugMicroTask(JSContext* cx, const MicroTask& entry);
 JS_PUBLIC_API bool PrependMicroTask(JSContext* cx, const MicroTask& entry);
diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
@@ -1212,10 +1212,9 @@ bool CycleCollectedJSContext::PerformMicroTaskCheckPoint(bool aForce) {
         }
         didProcess = true;
 
-        // Note: We're dropping the return value on the floor here. This is
-        // consistent with the previous implementation, which left the
-        // exception if it was there pending on the context, but likely should
-        // be changed.
+        // Note: We're dropping the return value on the floor here, however
+        // cleanup and exception handling are done as part of the CallSetup
+        // destructor if necessary.
         (void)RunMicroTask(cx, &job);
       }
     }