LibWebView+LibCore: Manage process lifecycle using a SIGCHLD handler

This large commit also refactors LibWebView's process handling to use
a top-level Application class that uses a new WebView::Process class to
encapsulate the IPC-centric nature of each helper process.

Userland/Libraries/LibWebView/Application.cpp

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2024, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Debug.h>
+#include <LibImageDecoderClient/Client.h>
+#include <LibWebView/Application.h>
+#include <LibWebView/WebContentClient.h>
+
+namespace WebView {
+
+Application* Application::s_the = nullptr;
+
+Application::Application(int, char**)
+{
+    VERIFY(!s_the);
+    s_the = this;
+
+    m_process_manager.on_process_exited = [this](Process&& process) {
+        process_did_exit(move(process));
+    };
+}
+
+Application::~Application()
+{
+    s_the = nullptr;
+}
+
+int Application::exec()
+{
+    int ret = m_event_loop.exec();
+    m_in_shutdown = true;
+    return ret;
+}
+
+void Application::add_child_process(WebView::Process&& process)
+{
+    m_process_manager.add_process(move(process));
+}
+
+#if defined(AK_OS_MACH)
+void Application::set_process_mach_port(pid_t pid, Core::MachPort&& port)
+{
+    m_process_manager.set_process_mach_port(pid, move(port));
+}
+#endif
+
+Optional<Process&> Application::find_process(pid_t pid)
+{
+    return m_process_manager.find_process(pid);
+}
+
+void Application::update_process_statistics()
+{
+    m_process_manager.update_all_process_statistics();
+}
+
+String Application::generate_process_statistics_html()
+{
+    return m_process_manager.generate_html();
+}
+
+void Application::process_did_exit(Process&& process)
+{
+    if (m_in_shutdown)
+        return;
+
+    dbgln_if(WEBVIEW_PROCESS_DEBUG, "Process {} died, type: {}", process.pid(), process_name_from_type(process.type()));
+
+    switch (process.type()) {
+    case ProcessType::ImageDecoder:
+        if (auto client = process.client<ImageDecoderClient::Client>(); client.has_value()) {
+            dbgln_if(WEBVIEW_PROCESS_DEBUG, "Restart ImageDecoder process");
+            if (auto on_death = move(client->on_death)) {
+                on_death();
+            }
+        }
+        break;
+    case ProcessType::RequestServer:
+        dbgln_if(WEBVIEW_PROCESS_DEBUG, "FIXME: Restart request server");
+        break;
+    case ProcessType::WebContent:
+        if (auto client = process.client<WebContentClient>(); client.has_value()) {
+            dbgln_if(WEBVIEW_PROCESS_DEBUG, "Restart WebContent process");
+            if (auto on_web_content_process_crash = move(client->on_web_content_process_crash))
+                on_web_content_process_crash();
+        }
+        break;
+    case ProcessType::WebWorker:
+        dbgln_if(WEBVIEW_PROCESS_DEBUG, "WebWorker {} died, not sure what to do.", process.pid());
+        break;
+    case ProcessType::Chrome:
+        dbgln("Invalid process type to be dying: Chrome");
+        VERIFY_NOT_REACHED();
+    }
+}
+
+}