[英]Running an asynchronous function in a GNOME extension
我想在 GNOME 扩展中运行一个循环。 在 DBus 服务方法调用之后,但 gnome shell 冻结
我了解到扩展在 GLib 的主循环中运行,我应该使用GTask API ,但我找不到使用它的方法,也找不到明确的例子。
我想我不能使用GLib.spawn_async_with_pipes
因为我不想调用命令,而是调用同一个类中的函数
代码示例:
class Foo { constructor () { this._ownName() } _ownName () { Gio.bus_own_name( Gio.BusType.SESSION, 'net.foo', Gio.BusNameOwnerFlags.NONE, this._onBusAcquired.bind(this), this._noOp, this._noOp ) } _onBusAcquired(connection) { connection.register_object( '/net/foo', GioInterface, this._methodCallClosure.bind(this), this._noOp, this._noOp ) _methodCallClosure(connection, sender, objectPath, interfaceName, methodName, parameters, invocation) { this._listen = true this._runLoop() invocation.return_value(null) } // this function should not block GLib's Main Loop _runLoop () { while(this._listen) { ... } } }
可能有多种方法可以避免阻塞主循环,但最好的方法可能取决于什么事件会导致中断while
循环。
如果您真的需要“轮询”某些条件,我认为最简单的方法可能是超时循环:
function myPollingFunc(arg1, arg2) {
if (the_event_occured) {
// Here is where you will invoke whatever it is you want to do
// when the event occurs, then destroy the source since the
// condition has been met.
this.classMethod(arg1, arg2);
return GLib.SOURCE_REMOVE;
}
// If the condition was not met, you can wait until the next loop and
// check again.
return GLib.SOURCE_CONTINUE;
}
// Probably you'll want to store this ID (maybe as a property on your class),
// so you can destroy the source if the DBus service is destroyed before the
// event you're waiting for occurs.
let sourceId;
sourceId = GLib.timeout_add_seconds(
// Generally this priority is fine, but you may choose another lower one
// if that makes sense
GLib.PRIORITY_DEFAULT,
// The timeout interval of your loop. As described in the linked article,
// second-based loops tend to be a better choice in terms of performance,
// however note that at least one interval will pass before the callback
// is invoked.
1,
// Your callback function. Since you're probably creating the source from
// a class method and intend on modifying some internal state of your class
// you can bind the function to the class scope, making it's internal state
// and other methods available to your callback.
//
// Function.bind() also allows you to prepend arguments to the callback, if
// that's necessary or a better choice. As noted above, you'll probably want
// to store the ID, which is especially important if you bind the callback to
// `this`.
//
// The reason is that the callback will hold a reference to the object it's
// bound to (`this` === `Foo`), and the source will hold the callback in the
// loop. So if you lose track of the source and the ability to destroy it, the
// object will never be garbage collected.
myPollingFunc.bind(this, arg1, arg2)
);
您可以对空闲源执行相同的操作,它会等待直到没有更高优先级的事件挂起而不是固定超时。 空闲源的问题是,如果没有其他未决事件,您的回调将几乎与while
循环一样快地重复调用,并且您可能会耗尽主循环(例如,使其他事件难以获得支持)在门口)。
另一方面,如果您实际上不需要轮询条件,而是等待发出信号或等待 GObject 属性更改,则可能有更直接的方法来执行此操作:
...
_runLoop () {
// Waiting for some object to emit a signal or change a property
let handlerId = someObject.connect('some-signal', () => {
someObject.disconnect(handlerId);
this.classMethod(arg1, arg2);
});
let propId = someGObject.connect('notify::some-prop', () => {
if (someGObject.some_prop === 'expected_value') {
someGObject.disconnect(propId);
this.classMethod(arg1, arg2);
}
});
}
...
在不知道您正在等待什么类型的事件或条件的情况下,很难就最佳解决方案提供更好的建议,但也许这会有所帮助。 我会说一般来说,如果您认为要在某些条件下循环,那么最好在现有 GLib 主循环中检查该条件,而不是创建自己的子循环。
编辑
有了更多的上下文,似乎您将依赖外部流程,以一种或另一种方式。 在这种情况下,我强烈建议避免在 GLib 中使用较低级别的 spawn 函数,而是使用 GSubprocess。
对于更高级别的语言绑定,这是一个更安全的选择,并且还包括用 C 编写的辅助函数,您可能最终会重写这些函数:
onProcExited(proc, result) {
try {
proc.wait_check_finish(proc, result);
} catch (e) {
logError(e);
}
}
onLineRead(stdout, result) {
try {
let line = stdout.read_line_finish_utf8(result)[0];
// %null generally means end of stream
if (line !== null) {
// Here you can do whatever processing on the line
// you need to do, and this will be non-blocking as
// all the I/O was done in a thread.
someFunc(line);
// Now you can request the next line
stdout.read_line_async(null, onLineRead.bind(this));
}
} catch (e) {
logError(e);
}
}
startFunc() {
this._proc = new Gio.Subprocess({
argv: ['proc_name', '--switch', 'arg', 'etc'],
flags: Gio.SubprocessFlags.STDOUT_PIPE
});
this._proc.init(null);
// Get the stdout pipe and wrap it in a buffered stream
// with some useful helpers
let stdout = new Gio.DataInputStream({
base_stream: this._proc.get_stdout_pipe()
});
// This function will spawn dedicated a thread, reading and buffering
// bytes until it finds a line ending and then invoke onLineRead() in
// in the main thread.
stdout.read_line_async(
GLib.PRIORITY_DEFAULT,
null // Cancellable, if you want it
onLineRead.bind(this)
);
// Check the process completion
this._proc.wait_check_async(null, onProcExited.bind(this));
}
编写这样的递归读取循环非常简单,GTask 函数( *_async()
/ *_finish()
)负责为您安排主循环中的回调。 所有 I/O 都在一个专用线程中完成,因此您处理输出的工作都是非阻塞的。
当您最终删除对this._proc
的引用时,您可以确信所有管道和资源都已正确清理,避免悬空文件描述符、僵尸进程等。 如果您需要提前退出流程,您可以随时调用Gio.Subprocess.force_exit()
。 读取循环本身将在 stdout 管道包装器上保存一个引用,因此您可以让它去做它的事情。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.