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Android: run save and load state on the CPU thread

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Saving a state from the pause menu aborted every assert-enabled build. The
screenshot the save embeds goes through MTGS::RunOnGSThread, which asserts it
is on the CPU thread, and the JNI entry point ran the whole save inline on
whatever thread the picker dispatched it from.

Parking the VM first, which is what these two entry points did, is not the
same guarantee. It stops the EE, but the MTGS ring's write position is
single-producer and owned by the CPU thread, and the CPU thread does not stop
producing when the VM is paused: its idle loop keeps draining
Host::PumpMessagesOnCPUThread() every 16 ms, so any GS-settings apply or window
resize queued from the UI pushes to the same ring the save is pushing to. Two
producers claiming one slot drops a packet, and a dropped data-packet header
leaves the GS thread parsing payload qwords as command tags.

So marshal both entry points with a blocking Host::RunOnCPUThread, matching
what commitSettings and changeDisc in the same file already do. The park stays:
it stops the EE for the inline zip and holds the audio pause the picker is
built around. Thread identity is what makes the ring pushes legal.

The load path is fixed alongside it. It has the identical violation — Freeze on
the way in, plus a recompiler cache reset — and goes unreported only because
MTGS::Freeze pushes its packet directly rather than through RunOnGSThread. Its
follow-up present moves into the same task, which also stops it racing the
resume in the pause guard's destructor.
This commit is contained in:
Brian Degenhardt
2026-08-02 21:20:12 -07:00
parent 112838e5fc
commit 9f73c77d59
1 changed files with 30 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files
platforms/android/app/src/main/cpp/native-lib.cpp
+30 -9
View File
@@ -2949,9 +2949,23 @@ Java_kr_co_iefriends_pcsx2_NativeApp_saveStateToSlot(JNIEnv *env, jclass clazz,
const ScopedVMPause pause_guard;
if (!pause_guard.parked())
return fail("cpu_thread_not_parked");
// Parking stops the EE, but it does not make THIS thread the CPU thread — and a save is not
// merely a read of VM state. SaveState_DownloadState freezes the GS through MTGS::Freeze, and
// the screenshot goes through MTGS::RunOnGSThread; both push to the MTGS ring, whose write
// position is single-producer and owned by the CPU thread. Pushing from JNI races whatever the
// CPU thread posts from its own paused idle loop, which keeps calling
// Host::PumpMessagesOnCPUThread() every 16 ms — a live GS-settings apply or a window resize
// queued from the UI lands there and pushes to the same ring. RunOnGSThread asserts exactly
// this, which is how it surfaced: an assert-enabled build aborts on the screenshot every time.
//
// So marshal, the way commitSettings and changeDisc above already do. The park stays: it stops
// the EE for the inline zip (zip_on_thread=false) and holds the audio pause the picker is built
// around. It is thread identity, not the park, that makes the ring pushes legal.
std::string save_error;
VMManager::SaveStateToSlot(p_slot, /*zip_on_thread=*/false,
[&save_error](const std::string& error) { save_error = error; });
Host::RunOnCPUThread([p_slot, &save_error]() {
VMManager::SaveStateToSlot(p_slot, /*zip_on_thread=*/false,
[&save_error](const std::string& error) { save_error = error; });
}, /*block=*/true);
if (!save_error.empty()) {
Console.Error("saveStateToSlot: %s", save_error.c_str());
return fail("save_error");
@@ -2997,16 +3011,23 @@ Java_kr_co_iefriends_pcsx2_NativeApp_loadStateFromSlot(JNIEnv *env, jclass clazz
const ScopedVMPause pause_guard;
if (!pause_guard.parked())
return fail("cpu_thread_not_parked");
const bool loaded = VMManager::LoadStateFromSlot(p_slot);
// Marshalled for the same reason as saveStateToSlot: a load pushes to the single-producer MTGS
// ring (MTGS::Freeze) and resets the recompiler code caches, both of which belong to the CPU
// thread. No assert fires on this one only because Freeze pushes its packet directly instead of
// going through RunOnGSThread — the violation is identical, it is just unpoliced.
//
// A normal LoadState does not present (only the input-recording path does), so the restored
// frame isn't shown until the game draws its next frame. When the game is already running
// that's the next vsync (imperceptible), but a load early in boot — before the present loop
// is flowing — otherwise leaves a black screen. Force the restored frame to display now.
// PresentCurrentFrame posts to the MTGS ring, so it goes through the CPU thread even though
// the park above has the EE stopped — MTGS.h says as much ("Should only be called from the
// CPU thread"). Not blocking: this is a cosmetic nudge, and the load itself already landed.
if (loaded)
Host::RunOnCPUThread([]() { MTGS::PresentCurrentFrame(); });
// is flowing — otherwise leaves a black screen. Force the restored frame to display now, in
// this same task: it is one more ring push, so it wants the same thread, and running it here
// rather than as a second queued job also stops it racing the resume in the pause guard's dtor.
bool loaded = false;
Host::RunOnCPUThread([p_slot, &loaded]() {
loaded = VMManager::LoadStateFromSlot(p_slot);
if (loaded)
MTGS::PresentCurrentFrame();
}, /*block=*/true);
return loaded;
}