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Legacy Win32 debugger: fix the painting problem with a frame-scoped mutex

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Debugger windows (register list, disassembly view, memory view, breakpoint/
thread/module/stack lists, watch list) read CPU-thread-owned state directly
from the GUI thread's WM_PAINT/list-fill handlers, racing against the CPU
thread. Routing every read through Core_RunOnCPUThread would be too slow for
something invoked continuously on paint/list-refresh.

Add g_frameMutex (Core.h/Core.cpp), held by NativeFrame() only across the
span where it actually touches that state (running the CPU, processing
breakpoints, running the ImGui debugger) - not across input handling or the
present/frame-pacing waits. Debugger windows now hold the same mutex while
reading, giving synchronized reads without the round-trip cost of queuing
to the CPU thread.

CtrlRegisterList::onPaint() goes back to always reading live values (now
safe under the lock) and grays them out by color alone while the core is
running, rather than the earlier snapshot-caching approach.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Hqm11k99viLfbJm2MkH4BH
This commit is contained in:
Henrik Rydgård
2026-08-08 17:22:12 +02:00
co-authored by Claude Sonnet 5
parent 03dcfd3931
commit f72709feb0
10 changed files with 129 additions and 38 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Windows/Debugger/Debugger_Lists.cpp
+36 -10
View File
@@ -255,7 +255,13 @@ void CtrlThreadList::OnRightClick(int itemIndex, int column, const POINT& point)
void CtrlThreadList::reloadThreads()
{
threads = GetThreadsInfo();
// Reading live kernel thread state here on the GUI thread would otherwise race with the CPU
// thread - hold g_frameMutex for the duration of the read, which NativeFrame() also holds
// while it's actually touching that state. See g_frameMutex in Core.h.
{
std::lock_guard<std::mutex> frameGuard(g_frameMutex);
threads = GetThreadsInfo();
}
Update();
}
@@ -325,9 +331,13 @@ bool CtrlBreakpointList::WindowMessage(UINT msg, WPARAM wParam, LPARAM lParam, L
void CtrlBreakpointList::reloadBreakpoints()
{
// Update the items we're displaying from the debugger.
displayedBreakPoints_ = g_breakpoints.GetBreakpoints();
displayedMemChecks_= g_breakpoints.GetMemChecks();
// Update the items we're displaying from the debugger. g_frameMutex guards this against races
// with the CPU thread - see g_frameMutex in Core.h.
{
std::lock_guard<std::mutex> frameGuard(g_frameMutex);
displayedBreakPoints_ = g_breakpoints.GetBreakpoints();
displayedMemChecks_= g_breakpoints.GetMemChecks();
}
for (int i = 0; i < GetRowCount(); i++)
{
@@ -744,11 +754,16 @@ void CtrlStackTraceView::OnDoubleClick(int itemIndex, int column)
}
void CtrlStackTraceView::loadStackTrace() {
auto memLock = Memory::Lock();
Memory::MemoryInitedLock memLock = Memory::Lock();
if (!PSP_IsInited())
return;
auto threads = GetThreadsInfo();
// Reading live thread/register/stack state here on the GUI thread would otherwise race with
// the CPU thread - hold g_frameMutex for the duration of the read, which NativeFrame() also
// holds while it's actually touching that state. See g_frameMutex in Core.h.
std::lock_guard<std::mutex> frameGuard(g_frameMutex);
std::vector<DebugThreadInfo> threads = GetThreadsInfo();
u32 entry = 0, stackTop = 0;
for (size_t i = 0; i < threads.size(); i++)
@@ -835,10 +850,16 @@ void CtrlModuleList::OnDoubleClick(int itemIndex, int column)
void CtrlModuleList::loadModules()
{
if (g_symbolMap) {
modules = g_symbolMap->getAllModules();
} else {
modules.clear();
// Reading the live symbol map here on the GUI thread would otherwise race with the CPU thread -
// hold g_frameMutex for the duration of the read, which NativeFrame() also holds while it's
// actually touching that state. See g_frameMutex in Core.h.
{
std::lock_guard<std::mutex> frameGuard(g_frameMutex);
if (g_symbolMap) {
modules = g_symbolMap->getAllModules();
} else {
modules.clear();
}
}
Update();
}
@@ -855,6 +876,11 @@ CtrlWatchList::CtrlWatchList(HWND hwnd, DebugInterface *cpu)
}
void CtrlWatchList::RefreshValues() {
// Evaluating watch expressions reads live registers/memory here on the GUI thread, which would
// otherwise race with the CPU thread - hold g_frameMutex for the duration, which NativeFrame()
// also holds while it's actually touching that state. See g_frameMutex in Core.h.
std::lock_guard<std::mutex> frameGuard(g_frameMutex);
int steppingCounter = Core_GetSteppingCounter();
int changes = false;
for (auto &watch : watches_) {