Unused export plugins are polling in the background

[rcorre]

Godot version

3.4.4.stable.arch_linux

System information

Linux 5.16.16-arch1-1

Issue description

While looking into #35868, I noticed that the Javascript, IOS, and Android exporters are in a constant poll loop as soon as I start the editor. They're not consuming an excessive amount of CPU, so it isn't a huge deal, but would it be worth starting the threads only if you have an export target for that platform?

godot/platform/iphone/export/export.cpp

Lines 144 to 178 in 242c05d

	static void _check_for_changes_poll_thread(void *ud) {
	EditorExportPlatformIOS *ea = (EditorExportPlatformIOS *)ud;
	while (!ea->quit_request.is_set()) {
	// Nothing to do if we already know the plugins have changed.
	if (!ea->plugins_changed.is_set()) {
	ea->plugins_lock.lock();
	Vector<PluginConfigIOS> loaded_plugins = get_plugins();
	if (ea->plugins.size() != loaded_plugins.size()) {
	ea->plugins_changed.set();
	} else {
	for (int i = 0; i < ea->plugins.size(); i++) {
	if (ea->plugins[i].name != loaded_plugins[i].name || ea->plugins[i].last_updated != loaded_plugins[i].last_updated) {
	ea->plugins_changed.set();
	break;
	}
	}
	}
	ea->plugins_lock.unlock();
	}
	uint64_t wait = 3000000;
	uint64_t time = OS::get_singleton()->get_ticks_usec();
	while (OS::get_singleton()->get_ticks_usec() - time < wait) {
	OS::get_singleton()->delay_usec(300000);
	if (ea->quit_request.is_set()) {
	break;
	}
	}
	}
	}

Thread 9 (Thread 0x7fffb77fe640 (LWP 83945) "godot.x11.opt.t"):
#0  0x00007ffff7b64a55 in clock_nanosleep@GLIBC_2.2.5 () from /usr/lib/libc.so.6
#1  0x00007ffff7b69717 in nanosleep () from /usr/lib/libc.so.6
#2  0x00000000013f7270 in OS_Unix::delay_usec (this=<optimized out>, p_usec=<optimized out>) at drivers/unix/os_unix.cpp:243
#3  0x0000000001d5f9ed in EditorExportPlatformJavaScript::_server_thread_poll (data=0x9a1a430) at platform/javascript/export/export.cpp:966
#4  0x0000000003179a05 in Thread::callback (p_self=<optimized out>, p_settings=..., p_callback=0x1d5f9c0 <EditorExportPlatformJavaScript::_server_thread_poll(void*)>, p_userdata=0x9a1a430) at core/os/thread.cpp:77
#5  0x00000000034d3ed4 in execute_native_thread_routine ()
#6  0x00007ffff7b195c2 in start_thread () from /usr/lib/libc.so.6
#7  0x00007ffff7b9e584 in clone () from /usr/lib/libc.so.6

Thread 8 (Thread 0x7fffb7fff640 (LWP 83944) "godot.x11.opt.t"):
#0  0x00007ffff7b64a55 in clock_nanosleep@GLIBC_2.2.5 () from /usr/lib/libc.so.6
#1  0x00007ffff7b69717 in nanosleep () from /usr/lib/libc.so.6
#2  0x00000000013f7270 in OS_Unix::delay_usec (this=<optimized out>, p_usec=<optimized out>) at drivers/unix/os_unix.cpp:243
#3  0x0000000001d58c86 in EditorExportPlatformIOS::_check_for_changes_poll_thread (ud=0xa427e00) at platform/iphone/export/export.cpp:171
#4  0x0000000003179a05 in Thread::callback (p_self=<optimized out>, p_settings=..., p_callback=0x1d58b70 <EditorExportPlatformIOS::_check_for_changes_poll_thread(void*)>, p_userdata=0xa427e00) at core/os/thread.cpp:77
#5  0x00000000034d3ed4 in execute_native_thread_routine ()
#6  0x00007ffff7b195c2 in start_thread () from /usr/lib/libc.so.6
#7  0x00007ffff7b9e584 in clone () from /usr/lib/libc.so.6

Thread 7 (Thread 0x7fffbcb38640 (LWP 83943) "godot.x11.opt.t"):
#0  0x00007ffff7b64a55 in clock_nanosleep@GLIBC_2.2.5 () from /usr/lib/libc.so.6
#1  0x00007ffff7b69717 in nanosleep () from /usr/lib/libc.so.6
#2  0x00000000013f7270 in OS_Unix::delay_usec (this=<optimized out>, p_usec=<optimized out>) at drivers/unix/os_unix.cpp:243
#3  0x0000000001d0af43 in EditorExportPlatformAndroid::_check_for_changes_poll_thread (ud=0x9f59d30) at platform/android/export/export_plugin.cpp:380
#4  0x0000000003179a05 in Thread::callback (p_self=<optimized out>, p_settings=..., p_callback=0x1d0adc0 <EditorExportPlatformAndroid::_check_for_changes_poll_thread(void*)>, p_userdata=0x9f59d30) at core/os/thread.cpp:77
#5  0x00000000034d3ed4 in execute_native_thread_routine ()
#6  0x00007ffff7b195c2 in start_thread () from /usr/lib/libc.so.6
#7  0x00007ffff7b9e584 in clone () from /usr/lib/libc.so.6

Moved from godotengine/godot-proposals#4241.

Steps to reproduce

1. Build godot with debug symbols
2. Start a new project
3. Pause with the debugger
4. List threads

Minimal reproduction project

No response