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/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil; -*- */
// SPDX-License-Identifier: MIT OR LGPL-2.0-or-later
// SPDX-FileCopyrightText: 2008 litl, LLC
// SPDX-FileCopyrightText: 2021 Canonical Ltd.
// SPDX-FileContributor: Marco Trevisan <marco.trevisan@canonical.com>
#include <config.h>
#include <glib.h> // for g_assert
#include <js/CallAndConstruct.h>
#include <js/Realm.h>
#include <js/RootingAPI.h>
#include <js/TypeDecls.h>
#include <js/Value.h>
#include "gi/closure.h"
#include "cjs/context-private.h"
#include "cjs/jsapi-util-root.h"
#include "cjs/jsapi-util.h"
#include "cjs/mem-private.h"
#include "util/log.h"
namespace Gjs {
Closure::Closure(JSContext* cx, JSObject* callable, bool root,
const char* description GJS_USED_VERBOSE_GCLOSURE)
: m_cx(cx) {
GJS_INC_COUNTER(closure);
GClosureNotify closure_notify;
if (root) {
// Fully manage closure lifetime if so asked
auto* gjs = GjsContextPrivate::from_cx(cx);
g_assert(cx == gjs->context());
m_callable.root(cx, callable);
gjs->register_notifier(global_context_notifier_cb, this);
closure_notify = [](void*, GClosure* closure) {
static_cast<Closure*>(closure)->closure_invalidated();
};
} else {
// Only mark the closure as invalid if memory is managed
// outside (i.e. by object.c for signals)
m_callable = callable;
closure_notify = [](void*, GClosure* closure) {
static_cast<Closure*>(closure)->closure_set_invalid();
};
}
g_closure_add_invalidate_notifier(this, nullptr, closure_notify);
gjs_debug_closure("Create closure %p which calls callable %p '%s'", this,
m_callable.debug_addr(), description);
}
/*
* Memory management of closures is "interesting" because we're keeping around
* a JSContext* and then trying to use it spontaneously from the main loop.
* I don't think that's really quite kosher, and perhaps the problem is that
* (in xulrunner) we just need to save a different context.
*
* Or maybe the right fix is to create our own context just for this?
*
* But for the moment, we save the context that was used to create the closure.
*
* Here's the problem: this context can be destroyed. AFTER the
* context is destroyed, or at least potentially after, the objects in
* the context's global object may be garbage collected. Remember that
* JSObject* belong to a runtime, not a context.
*
* There is apparently no robust way to track context destruction in
* SpiderMonkey, because the context can be destroyed without running
* the garbage collector, and xulrunner takes over the JS_SetContextCallback()
* callback. So there's no callback for us.
*
* So, when we go to use our context, we iterate the contexts in the runtime
* and see if ours is still in the valid list, and decide to invalidate
* the closure if it isn't.
*
* The closure can thus be destroyed in several cases:
* - invalidation by unref, e.g. when a signal is disconnected, closure is unref'd
* - invalidation because we were invoked while the context was dead
* - invalidation through finalization (we were garbage collected)
*
* These don't have to happen in the same order; garbage collection can
* be either before, or after, context destruction.
*
*/
void Closure::unset_context() {
if (!m_cx)
return;
if (m_callable && m_callable.rooted()) {
auto* gjs = GjsContextPrivate::from_cx(m_cx);
gjs->unregister_notifier(global_context_notifier_cb, this);
}
m_cx = nullptr;
}
void Closure::global_context_finalized() {
gjs_debug_closure(
"Context global object destroy notifier on closure %p which calls "
"callable %p",
this, m_callable.debug_addr());
if (m_callable) {
// Manually unset the context as we don't need to unregister the
// notifier here, or we'd end up touching a vector we're iterating
m_cx = nullptr;
reset();
// Notify any closure reference holders they
// may want to drop references.
g_closure_invalidate(this);
}
}
/* Invalidation is like "dispose" - it is guaranteed to happen at
* finalize, but may happen before finalize. Normally, g_closure_invalidate()
* is called when the "target" of the closure becomes invalid, so that the
* source (the signal connection, say can be removed.) The usage above
* in global_context_finalized() is typical. Since the target of the closure
* is under our control, it's unlikely that g_closure_invalidate() will ever
* be called by anyone else, but in case it ever does, it's slightly better
* to remove the "keep alive" here rather than in the finalize notifier.
*
* Unlike "dispose" invalidation only happens once.
*/
void Closure::closure_invalidated() {
GJS_DEC_COUNTER(closure);
gjs_debug_closure("Invalidating closure %p which calls callable %p", this,
m_callable.debug_addr());
if (!m_callable) {
gjs_debug_closure(" (closure %p already dead, nothing to do)", this);
return;
}
/* The context still exists, remove our destroy notifier. Otherwise we
* would call the destroy notifier on an already-freed closure.
*
* This happens in the normal case, when the closure is
* invalidated for some reason other than destruction of the
* JSContext.
*/
gjs_debug_closure(
" (closure %p's context was alive, "
"removing our destroy notifier on global object)",
this);
reset();
}
void Closure::closure_set_invalid() {
gjs_debug_closure("Invalidating signal closure %p which calls callable %p",
this, m_callable.debug_addr());
m_callable.prevent_collection();
reset();
GJS_DEC_COUNTER(closure);
}
bool Closure::invoke(JS::HandleObject this_obj,
const JS::HandleValueArray& args,
JS::MutableHandleValue retval) {
if (!m_callable) {
/* We were destroyed; become a no-op */
reset();
return false;
}
JSAutoRealm ar{m_cx, m_callable.get()};
if (gjs_log_exception(m_cx)) {
gjs_debug_closure(
"Exception was pending before invoking callback??? "
"Not expected - closure %p",
this);
}
JS::RootedValue v_callable{m_cx, JS::ObjectValue(*m_callable.get())};
bool ok = JS::Call(m_cx, this_obj, v_callable, args, retval);
GjsContextPrivate* gjs = GjsContextPrivate::from_cx(m_cx);
if (!ok) {
/* Exception thrown... */
gjs_debug_closure(
"Closure invocation failed (exception should have been thrown) "
"closure %p callable %p",
this, m_callable.debug_addr());
return false;
}
if (gjs_log_exception_uncaught(m_cx)) {
gjs_debug_closure(
"Closure invocation succeeded but an exception was set"
" - closure %p",
m_cx);
}
gjs->schedule_gc_if_needed();
return true;
}
} // namespace Gjs
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