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Fix vm.create child VMs missing native libs and make spawned runtimes libuv-safe #692

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Fix vm.create child VMs missing native libs and make spawned runtimes libuv-safe #692

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4c19f0e
VM fixes
Nicell Dec 14, 2025
4834e3d
fixes
Nicell Dec 14, 2025
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6 changes: 5 additions & 1 deletion lute/cli/src/climain.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -163,7 +163,11 @@ bool runBytecode(

lua_pop(GL, 1);

return runtime.runToCompletion();
bool success = runtime.runToCompletion();
if (success)
waitForSpawnedRuntimes();

return success;
}

static bool runFile(Runtime& runtime, const char* name, lua_State* GL, int program_argc, char** program_argv, LuteReporter& reporter)
Expand Down
30 changes: 19 additions & 11 deletions lute/fs/src/fs.cpp
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Expand Up @@ -233,7 +233,8 @@ int open(lua_State* L)
int fs_remove(lua_State* L)
{
uv_fs_t unlink_req;
int err = uv_fs_unlink(uv_default_loop(), &unlink_req, luaL_checkstring(L, 1), nullptr);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
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@Vighnesh-V Vighnesh-V Jan 7, 2026

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Probably don't want to re-interpret cast here - this should just be a uv_loop_t.

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@Vighnesh-V Vighnesh-V Jan 7, 2026

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  • ditto for all the places below.

int err = uv_fs_unlink(loop, &unlink_req, luaL_checkstring(L, 1), nullptr);
uv_fs_req_cleanup(&unlink_req);

if (err)
Expand All @@ -248,7 +249,8 @@ int fs_mkdir(lua_State* L)
int mode = luaL_optinteger(L, 2, 0777);

uv_fs_t req;
int err = uv_fs_mkdir(uv_default_loop(), &req, path, mode, nullptr);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int err = uv_fs_mkdir(loop, &req, path, mode, nullptr);
uv_fs_req_cleanup(&req);

if (err)
Expand All @@ -262,7 +264,8 @@ int fs_rmdir(lua_State* L)
const char* path = luaL_checkstring(L, 1);

uv_fs_t rmdir_req;
int err = uv_fs_rmdir(uv_default_loop(), &rmdir_req, path, nullptr);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int err = uv_fs_rmdir(loop, &rmdir_req, path, nullptr);
uv_fs_req_cleanup(&rmdir_req);

if (err)
Expand All @@ -276,7 +279,8 @@ int fs_stat(lua_State* L)
const char* path = luaL_checkstring(L, 1);

uv_fs_t stat_req;
int err = uv_fs_stat(uv_default_loop(), &stat_req, path, nullptr);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int err = uv_fs_stat(loop, &stat_req, path, nullptr);

if (err)
{
Expand Down Expand Up @@ -353,7 +357,8 @@ int fs_copy(lua_State* L)
auto* req = new uv_fs_t();
req->data = new ResumeToken(getResumeToken(L));

int err = uv_fs_copyfile(uv_default_loop(), req, path, dest, 0, defaultCallback);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int err = uv_fs_copyfile(loop, req, path, dest, 0, defaultCallback);

if (err)
{
Expand All @@ -373,7 +378,8 @@ int fs_link(lua_State* L)
auto* req = new uv_fs_t();
req->data = new ResumeToken(getResumeToken(L));

int err = uv_fs_link(uv_default_loop(), req, path, dest, defaultCallback);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int err = uv_fs_link(loop, req, path, dest, defaultCallback);

if (err)
{
Expand Down Expand Up @@ -402,7 +408,8 @@ int fs_symlink(lua_State* L)
req->flags = 0;
}

int err = uv_fs_symlink(uv_default_loop(), req, path, dest, req->flags, defaultCallback);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int err = uv_fs_symlink(loop, req, path, dest, req->flags, defaultCallback);

if (err)
{
Expand Down Expand Up @@ -474,7 +481,8 @@ int fs_watch(lua_State* L)
event->callbackReference = std::make_shared<Ref>(L, 2);
event->handle.data = event;

int init_err = uv_fs_event_init(uv_default_loop(), &event->handle);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
int init_err = uv_fs_event_init(loop, &event->handle);

if (init_err)
{
Expand Down Expand Up @@ -539,7 +547,7 @@ int fs_exists(lua_State* L)
req->data = new ResumeToken(getResumeToken(L));

int err = uv_fs_access(
uv_default_loop(),
reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop()),
req,
path,
F_OK,
Expand Down Expand Up @@ -578,7 +586,7 @@ int type(lua_State* L)

uv_fs_t req;

int err = uv_fs_stat(uv_default_loop(), &req, path, nullptr);
int err = uv_fs_stat(reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop()), &req, path, nullptr);

if (err)
{
Expand All @@ -601,7 +609,7 @@ int listdir(lua_State* L)
req->data = new ResumeToken(getResumeToken(L));

int err = uv_fs_scandir(
uv_default_loop(),
reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop()),
req,
path,
0,
Expand Down
19 changes: 13 additions & 6 deletions lute/fs/src/fs_impl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ struct FSRead : FSRequest
: FSRequest(L)
, file(file)
{
loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
chunk.resize(kChunkIOSize);
iov = uv_buf_init(chunk.data(), chunk.size());
buffer.reserve(kChunkIOSize);
Expand All @@ -28,6 +29,7 @@ struct FSRead : FSRequest
static void readCallback(uv_fs_t* req);

UVFile* file = nullptr;
uv_loop_t* loop = nullptr;
std::vector<char> buffer;
std::vector<char> chunk;
uv_buf_t iov;
Expand All @@ -41,12 +43,14 @@ struct FSWrite : FSRequest
, toWrite(buf, buf + len)
, offset(0)
{
loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
chunk.resize(kChunkIOSize);
}

static void writeCallback(uv_fs_t* req);

UVFile* file = nullptr;
uv_loop_t* loop = nullptr;
std::vector<char> chunk;
uv_buf_t iov;
std::vector<char> toWrite;
Expand All @@ -59,6 +63,7 @@ struct FSClose : FSRequest
: FSRequest(L)
, file(file)
{
loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
}

~FSClose()
Expand All @@ -67,13 +72,15 @@ struct FSClose : FSRequest
}

UVFile* file = nullptr;
uv_loop_t* loop = nullptr;
};

int open_impl(lua_State* L, const char* path, int flags, int mode)
{
uvutils::ScopedUVRequest<FSRequest> req(L);
uv_loop_t* loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
uv_fs_open(
uv_default_loop(),
loop,
&req->req,
path,
flags,
Expand Down Expand Up @@ -134,7 +141,7 @@ void FSRead::readCallback(uv_fs_t* req)
std::fill(r->chunk.begin(), r->chunk.end(), 0);

uvutils::ScopedUVRequest<FSRead> scopedReq{std::move(r)};
uv_fs_read(uv_default_loop(), &scopedReq->req, scopedReq->file->fd.value(), &scopedReq->iov, 1, -1, FSRead::readCallback);
uv_fs_read(scopedReq->loop, &scopedReq->req, scopedReq->file->fd.value(), &scopedReq->iov, 1, -1, FSRead::readCallback);
}

void FSWrite::writeCallback(uv_fs_t* req)
Expand Down Expand Up @@ -167,7 +174,7 @@ void FSWrite::writeCallback(uv_fs_t* req)
w->iov = uv_buf_init(w->chunk.data(), chunkSize);

uvutils::ScopedUVRequest<FSWrite> scopedReq{std::move(w)};
uv_fs_write(uv_default_loop(), &scopedReq->req, scopedReq->file->fd.value(), &scopedReq->iov, 1, -1, FSWrite::writeCallback);
uv_fs_write(scopedReq->loop, &scopedReq->req, scopedReq->file->fd.value(), &scopedReq->iov, 1, -1, FSWrite::writeCallback);
}

int read_impl(lua_State* L, UVFile* handle)
Expand All @@ -178,7 +185,7 @@ int read_impl(lua_State* L, UVFile* handle)
}

uvutils::ScopedUVRequest<FSRead> req{L, handle};
uv_fs_read(uv_default_loop(), &req->req, handle->fd.value(), &req->iov, 1, -1, FSRead::readCallback);
uv_fs_read(req->loop, &req->req, handle->fd.value(), &req->iov, 1, -1, FSRead::readCallback);
// Automatically releases when req goes out of scope
return lua_yield(L, 0);
}
Expand All @@ -197,7 +204,7 @@ int write_impl(lua_State* L, UVFile* handle, const char* toWrite, size_t numByte
std::copy(req->toWrite.begin(), req->toWrite.begin() + chunkSize, req->chunk.begin());
req->iov = uv_buf_init(req->chunk.data(), chunkSize);

uv_fs_write(uv_default_loop(), &req->req, handle->fd.value(), &req->iov, 1, -1, FSWrite::writeCallback);
uv_fs_write(req->loop, &req->req, handle->fd.value(), &req->iov, 1, -1, FSWrite::writeCallback);

return lua_yield(L, 0);
}
Expand All @@ -211,7 +218,7 @@ int close_impl(lua_State* L, UVFile* handle)

uvutils::ScopedUVRequest<FSClose> req{L, handle};
uv_fs_close(
uv_default_loop(),
req->loop,
&req->req,
handle->fd.value(),
[](uv_fs_t* req)
Expand Down
2 changes: 1 addition & 1 deletion lute/io/src/io.cpp
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Expand Up @@ -82,7 +82,7 @@ static void onTtyRead(uv_stream_t* stream, ssize_t nread, const uv_buf_t* buf)
int read(lua_State* L)
{
auto handle = std::make_shared<IOHandle>();
handle->loop = uv_default_loop();
handle->loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
handle->resumeToken = getResumeToken(L);
handle->self = handle;

Expand Down
20 changes: 15 additions & 5 deletions lute/net/src/net.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
#include "uv.h"

#include <memory>
#include <mutex>
#include <optional>
#include <string>
#include <utility>
Expand Down Expand Up @@ -227,6 +228,7 @@ static const int kEmptyServerKey = 0;
static Luau::DenseHashMap<int, uWSApp> serverInstances(kEmptyServerKey);
static Luau::DenseHashMap<int, std::shared_ptr<struct ServerLoopState>> serverStates(kEmptyServerKey);
static int nextServerId = 1;
static std::mutex serverMutex;

struct ServerLoopState
{
Expand Down Expand Up @@ -500,6 +502,8 @@ void setupAppAndListen(auto* app, std::shared_ptr<ServerLoopState> state, bool&

bool closeServer(int serverId)
{
std::scoped_lock lock(serverMutex);

if (!serverInstances.contains(serverId) || !serverStates.contains(serverId))
{
return false;
Expand Down Expand Up @@ -530,8 +534,6 @@ bool closeServer(int serverId)

int lua_serve(lua_State* L)
{
uWS::Loop::get(uv_default_loop());

std::string hostname = "127.0.0.1";
int port = 3000;
bool reusePort = false;
Expand Down Expand Up @@ -618,8 +620,13 @@ int lua_serve(lua_State* L)
}

Runtime* runtime = getRuntime(L);
uWS::Loop::get(runtime->getUvLoop());

int serverId = nextServerId++;
int serverId = 0;
{
std::scoped_lock lock(serverMutex);
serverId = nextServerId++;
}

auto state = std::make_shared<ServerLoopState>();
state->runtime = runtime;
Expand Down Expand Up @@ -655,8 +662,11 @@ int lua_serve(lua_State* L)
return 0;
}

serverInstances[serverId] = std::move(app);
serverStates[serverId] = state;
{
std::scoped_lock lock(serverMutex);
serverInstances[serverId] = std::move(app);
serverStates[serverId] = state;
}

lua_createtable(L, 0, 3);

Expand Down
2 changes: 1 addition & 1 deletion lute/process/src/process.cpp
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Expand Up @@ -225,7 +225,7 @@ const std::string kStdioKindNone = "none";
int executionHelper(lua_State* L, std::vector<std::string> args, ProcessOptions opts)
{
auto handle = std::make_shared<ProcessHandle>();
handle->loop = uv_default_loop();
handle->loop = reinterpret_cast<uv_loop_t*>(getRuntime(L)->getUvLoop());
handle->self = handle;

uv_process_options_t options = {};
Expand Down
13 changes: 13 additions & 0 deletions lute/runtime/include/lute/runtime.h
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Expand Up @@ -14,6 +14,7 @@
#include <vector>

struct lua_State;
struct uv_loop_s;
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@Vighnesh-V Vighnesh-V Jan 7, 2026

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This is an internal libuv type - you'll want to store uv_loop_t


struct ThreadToContinue
{
Expand Down Expand Up @@ -44,6 +45,9 @@ struct Runtime
Runtime();
~Runtime();

bool useDedicatedUvLoop();
uv_loop_s* getUvLoop() const;
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@Vighnesh-V Vighnesh-V Jan 7, 2026

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Suggested change
uv_loop_s* getUvLoop() const;
uv_loop_t* getUVLoop() const;


bool runToCompletion();
RuntimeStep runOnce();

Expand Down Expand Up @@ -77,6 +81,9 @@ struct Runtime
// Shorthand for global state
lua_State* GL = nullptr;

// Event loop for this runtime; defaults to `uv_default_loop()`, but can be dedicated via `useDedicatedUvLoop`.
uv_loop_s* uvLoop = nullptr;
Comment on lines +84 to +85
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@Vighnesh-V Vighnesh-V Jan 7, 2026

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This adds a lot of complexity. Instead of defaulting, just initialize a uv_loop manually for this runtime.


std::mutex dataCopyMutex;
std::unique_ptr<lua_State, void (*)(lua_State*)> dataCopy;

Expand All @@ -92,6 +99,8 @@ struct Runtime
std::thread runLoopThread;

std::atomic<int> activeTokens;

bool ownsUvLoop = false;
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@Vighnesh-V Vighnesh-V Jan 7, 2026 •
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We could do one runtime, one loop - see my comment below, since we might not actually need this?

};

Runtime* getRuntime(lua_State* L);
Expand All @@ -114,3 +123,7 @@ struct ResumeTokenData
ResumeToken getResumeToken(lua_State* L);

lua_State* setupState(Runtime& runtime, std::function<void(lua_State*)> doBeforeSandbox);

// Track child runtimes created via `@lute/vm` so the CLI can stay alive when they have work (e.g. servers).
void registerSpawnedRuntime(const std::shared_ptr<Runtime>& runtime);
void waitForSpawnedRuntimes();
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