https://github.com/athierry-oct updated
https://github.com/llvm/llvm-project/pull/144919
>From 52cb93996bf3d59036b84acce96c649724cf8711 Mon Sep 17 00:00:00 2001
From: Adrien Thierry <adrien.thie...@octasic.com>
Date: Thu, 3 Jul 2025 10:13:28 -0400
Subject: [PATCH] [lldb] Transfer events from previous listener when hijacking
This patch addresses a race condition that can occur when a script using
the Python API calls SBProcess::Kill() around the same time a breakpoint
is hit.
If a stop event is broadcast before the hijack listener is installed, it
may be delivered to the default listener and missed entirely by the
hijack listener. This causes Process::WaitForProcessToStop() to hang
until it times out, waiting for a public stop event that is never
received.
To fix this, we now transfer all pending events from the original
listener to the hijack listener before hijacking, using a new
Listener::MoveEvents method. We also do the reverse operation when
restoring the original listener to avoid dropping any event.
---
lldb/include/lldb/Utility/Listener.h | 7 +++++++
lldb/source/Utility/Broadcaster.cpp | 27 +++++++++++++++++++++++++++
lldb/source/Utility/Listener.cpp | 28 ++++++++++++++++++++++++++++
3 files changed, 62 insertions(+)
diff --git a/lldb/include/lldb/Utility/Listener.h
b/lldb/include/lldb/Utility/Listener.h
index d48816ec0ea4d..e48d210a3a749 100644
--- a/lldb/include/lldb/Utility/Listener.h
+++ b/lldb/include/lldb/Utility/Listener.h
@@ -53,6 +53,13 @@ class Listener : public
std::enable_shared_from_this<Listener> {
void AddEvent(lldb::EventSP &event);
+ // Transfers all events matching the specified broadcaster and type to the
+ // destination listener. This can be useful when setting up a hijack
listener,
+ // to ensure that no relevant events are missed.
+ void MoveEvents(lldb::ListenerSP destination,
+ Broadcaster *broadcaster, // nullptr for any broadcaster
+ uint32_t event_type_mask);
+
void Clear();
const char *GetName() { return m_name.c_str(); }
diff --git a/lldb/source/Utility/Broadcaster.cpp
b/lldb/source/Utility/Broadcaster.cpp
index c6b2606afe0c8..9d545d46bade4 100644
--- a/lldb/source/Utility/Broadcaster.cpp
+++ b/lldb/source/Utility/Broadcaster.cpp
@@ -335,6 +335,19 @@ bool Broadcaster::BroadcasterImpl::HijackBroadcaster(
"{0} Broadcaster(\"{1}\")::HijackBroadcaster (listener(\"{2}\")={3})",
static_cast<void *>(this), GetBroadcasterName(),
listener_sp->m_name.c_str(), static_cast<void *>(listener_sp.get()));
+
+ // Move pending events from the previous listener to the
+ // hijack listener. This ensures that no relevant event queued before the
+ // transition is missed by the hijack listener.
+ ListenerSP prev_listener;
+ if (!m_hijacking_listeners.empty())
+ prev_listener = m_hijacking_listeners.back();
+ else if (m_primary_listener_sp)
+ prev_listener = m_primary_listener_sp;
+ if (prev_listener && listener_sp) {
+ prev_listener->MoveEvents(listener_sp, &m_broadcaster, event_mask);
+ }
+
m_hijacking_listeners.push_back(listener_sp);
m_hijacking_masks.push_back(event_mask);
return true;
@@ -367,6 +380,20 @@ void Broadcaster::BroadcasterImpl::RestoreBroadcaster() {
static_cast<void *>(this), GetBroadcasterName(),
listener_sp->m_name.c_str(),
static_cast<void *>(listener_sp.get()));
+
+ // Move any remaining events from the hijack listener back to
+ // the previous listener. This ensures that no events are dropped when
+ // restoring the original listener.
+ ListenerSP prev_listener;
+ if (m_hijacking_listeners.size() > 1)
+ prev_listener = m_hijacking_listeners[m_hijacking_listeners.size() - 2];
+ else if (m_primary_listener_sp)
+ prev_listener = m_primary_listener_sp;
+ if (listener_sp && prev_listener && !m_hijacking_masks.empty()) {
+ listener_sp->MoveEvents(prev_listener, &m_broadcaster,
+ m_hijacking_masks.back());
+ }
+
m_hijacking_listeners.pop_back();
}
if (!m_hijacking_masks.empty())
diff --git a/lldb/source/Utility/Listener.cpp b/lldb/source/Utility/Listener.cpp
index d4ce3bf25ec5a..448ecb9fcc3c4 100644
--- a/lldb/source/Utility/Listener.cpp
+++ b/lldb/source/Utility/Listener.cpp
@@ -176,6 +176,34 @@ void Listener::AddEvent(EventSP &event_sp) {
m_events_condition.notify_all();
}
+void Listener::MoveEvents(
+ ListenerSP destination,
+ Broadcaster *broadcaster, // nullptr for any broadcaster
+ uint32_t event_type_mask) {
+ Log *log = GetLog(LLDBLog::Events);
+
+ std::lock_guard<std::mutex> guard(m_events_mutex);
+ auto pos = m_events.begin();
+ while (pos != m_events.end()) {
+ EventSP &event_sp = *pos;
+ if (event_sp &&
+ ((broadcaster == nullptr) || event_sp->BroadcasterIs(broadcaster)) &&
+ (event_type_mask == 0 || event_type_mask & event_sp->GetType())) {
+ if (log)
+ LLDB_LOGF(
+ log, "%p Listener('%s')::MoveEvents moving event %p to %p('%s')",
+ static_cast<void *>(this), m_name.c_str(),
+ static_cast<void *>(event_sp.get()),
+ static_cast<void *>(destination.get()), destination->GetName());
+
+ destination->AddEvent(event_sp);
+ pos = m_events.erase(pos);
+ } else {
+ ++pos;
+ }
+ }
+}
+
bool Listener::FindNextEventInternal(
std::unique_lock<std::mutex> &lock,
Broadcaster *broadcaster, // nullptr for any broadcaster
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