I'm trying to share a Handler(for websocket communication) and its properties between different threads using Mutex and Arc.
let shared_server = Arc::new(Mutex::new(Server { out: None }));
let c_shared_server = shared_server.clone();
thread::spawn(move || {
listen(format!("{}:{}", String::from("127.0.0.1"), 3012), |out| {
c_shared_server.lock().unwrap().out = Some(out.clone());
move |msg| {
Ok(())
}
}).unwrap()
});
let ten_millis = time::Duration::from_millis(1000);
thread::sleep(ten_millis);
println!("{:?}", shared_server.lock().unwrap());
Server { out: None }
out shouldn't be None here, I want to use it then, any idea how i could accomplish this ?
Related
I'm use DataStore with flow but I cant get any update on the flow when editing DataStore.
Store.kt
private class IStore(private val context: Context): Store {
val eventIDKey = stringPreferencesKey("EventID")
override suspend fun setEventID(eventID: String) {
context.dataStoreSettings.edit { settings ->
settings[eventIDKey] = eventID
}
}
override fun getEventID(): Flow<String> {
return context.dataStoreSettings.data.map { settings -> settings[eventIDKey].orEmpty() }
}
}
and manipulate getEventID() with data from room database in event service
EventService.kt
fun getSelectedEventLive() = store.getEventID()
.onEach { Log.d("EventService", "income new event id $it") }
.flatMapConcat { if(it.isNotBlank()) eventDao.get(it) else flowOf(null) }
onEach called when I collect the data but when updated it's not called again and need to close and open the app to show the latest data
MainViewModel.kt
val selectedEvent = eventService.getSelectedEventLive()
.stateIn(viewModelScope, SharingStarted.Lazily, null)
and use on Compose with this
val currentEvent by mainViewModel.selectedEvent.collectAsState()
Maybe I doing wrong or maybe there is something I miss?
Usually, you want to use flow.collect {...}, since Flow is cold and need to know that it is being collected to start producing new values.
// MainViewModel.kt
private val _selectedEvent = MutableStateFlow<TypeOfYourEvent>()
val selectedEvent: StateFlow<TypeOfYourEvent> = _selectedEvent
init {
viewModelScope.launch {
getSelectedEventLive().collect { it ->
_selectedEvent.value = it
}
}
}
This example should be fine with your composable's code, you still can collect selectedEvent as state.
Yeah i found the solusion its works if i change the flatMapConcat with flatMapLatest in EventService.kt
fun getSelectedEventLive() = store.getEventID()
.filterNot { it.isBlank() }
.flatMapLatest { eventDao.get(it) }
I am trying to use Ether JS in my Flutter application. I know that it is not directly supported and even the existing implementations are not really well documented.
Is there any way I can use this library in my Flutter application for Android and iOS? Any other alternative suggestion is also welcome.
I have tried js.dart but could not figure out how to use it. I am not even sure if it is the right choice for this scenario.
I have also tried Flutter WebView Plugin.
plugin.evalJavascript(
'function add(a,b){return a+b;}add(2,3);'
).then((s) {
print(s);
}
This function rightly returns 5 as the response. But I do not understand how to use the EtherJS library like this.
I am a noob with Flutter, Dart and JS. Any help will be appreciated.
I eventually solved this by using Platform channels as suggested by rmtmckenzie in this answer.
I downloaded the JS file and saved it to android/app/src/main/res/raw/ether.js and ios/runner/ether.js for Android and iOS respectively.
Installing dependencies
Android
Add LiquidCore as a dependency in app level build.gradle
implementation 'com.github.LiquidPlayer:LiquidCore:0.5.0'
iOS
For iOS I used the JavaScriptCore which is part of the SDK.
Platform Channel
In my case, I needed to create a Wallet based on a Mnemonic (look up BIP39) I pass in into the JS function. For this, I created a Platform channel which passes in the Mnemonic (which is basically of type String) as an argument and will return a JSON object when done.
Future<dynamic> getWalletFromMnemonic({#required String mnemonic}) {
return platform.invokeMethod('getWalletFromMnemonic', [mnemonic]);
}
Android Implementation (Java)
Inside MainActivity.java add this after this line
GeneratedPluginRegistrant.registerWith(this);
String CHANNEL = "UNIQUE_CHANNEL_NAME";
new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler(
new MethodChannel.MethodCallHandler() {
#Override
public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) {
if (methodCall.method.equals("getWalletFromMnemonic")) {
ArrayList<Object> args = (ArrayList<Object>) methodCall.arguments;
String mnemonic = (String) args.get(0);
JSObject walletFromMnemonic = getWalletFromMnemonic(mnemonic);
if (walletFromMnemonic == null) {
result.error("Could not create", "Wallet generation failed", null);
return;
}
String privateKey = walletFromMnemonic.property("privateKey").toString();
String address = walletFromMnemonic.property("address").toString();
HashMap<String, String> map = new HashMap<>();
map.put("privateKey", privateKey);
map.put("address", address);
JSONObject obj = new JSONObject(map);
result.success(obj.toString());
} else {
result.notImplemented();
}
}
}
);
Declare the following methods which perform the actual action of interacting with the JS library and returning the result to the platform channel.
#Nullable
#VisibleForTesting
private JSObject getWalletFromMnemonic(String mnemonic) {
JSContext jsContext = getJsContext(getEther());
JSObject wallet = getWalletObject(jsContext);
if (wallet == null) {
return null;
}
if (!wallet.hasProperty("fromMnemonic")) {
return null;
}
JSFunction walletFunction = wallet.property("fromMnemonic").toObject().toFunction();
return walletFunction.call(null, mnemonic).toObject();
}
#Nullable
#VisibleForTesting
private JSObject getWalletObject(JSContext context) {
JSObject jsEthers = context.property("ethers").toObject();
if (jsEthers.hasProperty("Wallet")) {
return jsEthers.property("Wallet").toObject();
}
return null;
}
#VisibleForTesting
String getEther() {
String s = "";
InputStream is = getResources().openRawResource(R.raw.ether);
try {
s = IOUtils.toString(is);
} catch (IOException e) {
s = null;
e.printStackTrace();
} finally {
IOUtils.closeQuietly(is);
}
return s;
}
#VisibleForTesting
JSContext getJsContext(String code) {
JSContext context = new JSContext();
context.evaluateScript(code);
return context;
}
iOS Implementation (Swift)
Add the following lines in AppDelegate.swift inside the override application method.
final let methodChannelName: String = "UNIQUE_CHANNEL_NAME"
let controller: FlutterViewController = window?.rootViewController as! FlutterViewController
let methodChannel = FlutterMethodChannel.init(name: methodChannelName, binaryMessenger: controller)
methodChannel.setMethodCallHandler({
(call: FlutterMethodCall, result: FlutterResult)-> Void in
if call.method == "getWalletFromMnemonic" {
guard let mnemonic = call.arguments as? [String] else {
return
}
if let wallet = self.getWalletFromMnemonic(mnemonic: mnemonic[0]) {
result(wallet)
} else {
result("Invalid")
}
}
})
Add the logic to interact with the JavaScriptCore.
private func getWalletFromMnemonic(mnemonic: String) -> Dictionary<String, String>? {
let PRIVATE_KEY = "privateKey"
let ADDRESS = "address"
guard let jsContext = self.initialiseJS(jsFileName: "ether") else { return nil }
guard let etherObject = jsContext.objectForKeyedSubscript("ethers") else { return nil }
guard let walletObject = etherObject.objectForKeyedSubscript("Wallet") else { return nil }
guard let walletFromMnemonicObject = walletObject.objectForKeyedSubscript("fromMnemonic") else {
return nil
}
guard let wallet = walletFromMnemonicObject.call(withArguments: [mnemonic]) else { return nil }
guard let privateKey = wallet.forProperty(PRIVATE_KEY)?.toString() else { return nil }
guard let address = wallet.forProperty(ADDRESS)?.toString() else { return nil }
var walletDictionary = Dictionary<String, String>()
walletDictionary[ADDRESS] = address
walletDictionary[PRIVATE_KEY] = privateKey
return walletDictionary
}
private func initialiseJS(jsFileName: String) -> JSContext? {
let jsContext = JSContext()
guard let jsSourcePath = Bundle.main.path(forResource: jsFileName, ofType: "js") else {
return nil
}
do {
let jsSourceContents = try String(contentsOfFile: jsSourcePath)
jsContext!.evaluateScript(jsSourceContents)
return jsContext!
} catch {
print(error.localizedDescription)
}
return nil
}
Honestly, if you're new to Flutter, Dart, and JS you are going to have some trouble with this unless you're willing to invest a fair amount of time. It does depend on what exactly you're trying to make with the Ether JS library, but in general you're going to have a hard time integrating it with flutter. There is an Ethereum package but it seems much narrower in scope than the ether.js library you've been looking at - it mostly seems focused on communication with the RPC api rather than dealing with wallets etc.
If you're dead set on using Flutter, your best bet would be to use Android & iOS specific libraries to do the actual ethereum stuff and to communicate through Platform Channels to a common api in your dart code. This could be a significant undertaking depending on how much of the API you need to expose, especially for someone new to flutter/dart and possibly to android/ios development as well. This will be much more performant than communicating back and forth with javascript running in a webview though, and realistically probably easier to code as well because flutter doesn't really have any good mechanisms for calling js code right now.
There is another option - to use a different client UI framework entirely. React native might do everything you need and has the advantage of being in Javascript so it can most likely integrate the Ether.js library easily, although I can't guarantee that it will actually fully support the ether.js library (its runtime might not have the necessary crypto extensions for example).
Future<String> loadJS(String name) async {
var givenJS = rootBundle.loadString('assets/$name.js');
return givenJS.then((String js) {
flutterWebViewPlugin.onStateChanged.listen((viewState) async {
if (viewState.type == WebViewState.finishLoad) {
flutterWebViewPlugin.evalJavascript(js);
}
});
});
}
I need a read\write lock for my application. I've read https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock
and wrote my own class, cause there are no read/write lock in swift
class ReadWriteLock {
var logging = true
var b = 0
let r = "vdsbsdbs" // string1 for locking
let g = "VSDBVSDBSDBNSDN" // string2 for locking
func waitAndStartWriting() {
log("wait Writing")
objc_sync_enter(g)
log("enter writing")
}
func finishWriting() {
objc_sync_exit(g)
log("exit writing")
}
// ждет пока все чтение завершится чтобы начать чтение
// и захватить мютекс
func waitAndStartReading() {
log("wait reading")
objc_sync_enter(r)
log("enter reading")
b++
if b == 1 {
objc_sync_enter(g)
log("read lock writing")
}
print("b = \(b)")
objc_sync_exit(r)
}
func finishReading() {
objc_sync_enter(r)
b--
if b == 0 {
objc_sync_exit(g)
log("read unlock writing")
}
print("b = \(b)")
objc_sync_exit(r)
}
private func log(s: String) {
if logging {
print(s)
}
}
}
It works good, until i try to use it from GCD threads.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0)
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
When i try to use this class from different async blocks at some moment it allows to write when write is locked
here is sample log:
wait reading
enter reading
read lock writing
b = 1
wait reading
enter reading
b = 2
wait reading
enter reading
b = 3
wait reading
enter reading
b = 4
wait reading
enter reading
b = 5
wait reading
enter reading
b = 6
wait reading
enter reading
b = 7
wait reading
enter reading
b = 8
wait reading
enter reading
b = 9
b = 8
b = 7
b = 6
b = 5
wait Writing
enter writing
exit writing
wait Writing
enter writing
So, as you can see g was locked, but objc_sync_enter(g) allows to continue.
Why could this happen ?
BTW i checked how many times ReadWriteLock constructed, and it's 1.
Why objc_sync_exit not working and allowing to objc_sync_enter(g) when it's not freed ?
PS Readwirtelock defined as
class UserData {
static let lock = ReadWriteLock()
Thanks.
objc_sync_enter is an extremely low-level primitive, and isn't intended to be used directly. It's an implementation detail of the old #synchronized system in ObjC. Even that is extremely out-dated and should generally be avoided.
Synchronized access in Cocoa is best achieved with GCD queues. For example, this is a common approach that achieves a reader/writer lock (concurrent reading, exclusive writing).
public class UserData {
private let myPropertyQueue = dispatch_queue_create("com.example.mygreatapp.property", DISPATCH_QUEUE_CONCURRENT)
private var _myProperty = "" // Backing storage
public var myProperty: String {
get {
var result = ""
dispatch_sync(myPropertyQueue) {
result = self._myProperty
}
return result
}
set {
dispatch_barrier_async(myPropertyQueue) {
self._myProperty = newValue
}
}
}
}
All your concurrent properties can share a single queue, or you can give each property its own queue. It depends on how much contention you expect (a writer will lock the entire queue).
The "barrier" in "dispatch_barrier_async" means that it is the only thing allowed to run on the queue at that time, so all previous reads will have completed, and all future reads will be prevented until it completes. This scheme means that you can have as many concurrent readers as you want without starving writers (since writers will always be serviced), and writes are never blocking. On reads are blocking, and only if there is actual contention. In the normal, uncontested case, this is extremely very fast.
Are you 100% sure your blocks are actually executing on different threads?
objc_sync_enter() / objc_sync_exit() are guarding you only from object being accessed from different threads. They use a recursive mutex under the hood, so they won't either deadlock or prevent you from repeatedly accessing object from the same thread.
So if you lock in one async block and unlock in another one, the third block executed in-between can have access to the guarded object.
This is one of those very subtle nuances that is easy to miss.
Locks in Swift
You have to really careful what you use as a Lock. In Swift, String is a struct, meaning it's pass-by-value.
Whenever you call objc_sync_enter(g), you are not giving it g, but a copy of g. So each thread is essentially creating its own lock, which in effect, is like having no locking at all.
Use NSObject
Instead of using a String or Int, use a plain NSObject.
let lock = NSObject()
func waitAndStartWriting() {
log("wait Writing")
objc_sync_enter(lock)
log("enter writing")
}
func finishWriting() {
objc_sync_exit(lock)
log("exit writing")
}
That should take care of it!
In addition to #rob-napier's solution. I've updated this to Swift 5.1, added generic typing and a couple of convenient append methods. Note that only methods that access resultArray via get/set or append are thread safe, so I added a concurrent append also for my practical use case where the result data is updated over many result calls from instances of Operation.
public class ConcurrentResultData<E> {
private let resultPropertyQueue = dispatch_queue_concurrent_t.init(label: UUID().uuidString)
private var _resultArray = [E]() // Backing storage
public var resultArray: [E] {
get {
var result = [E]()
resultPropertyQueue.sync {
result = self._resultArray
}
return result
}
set {
resultPropertyQueue.async(group: nil, qos: .default, flags: .barrier) {
self._resultArray = newValue
}
}
}
public func append(element : E) {
resultPropertyQueue.async(group: nil, qos: .default, flags: .barrier) {
self._resultArray.append(element)
}
}
public func appendAll(array : [E]) {
resultPropertyQueue.async(group: nil, qos: .default, flags: .barrier) {
self._resultArray.append(contentsOf: array)
}
}
}
For an example running in a playground add this
//MARK:- helpers
var count:Int = 0
let numberOfOperations = 50
func operationCompleted(d:ConcurrentResultData<Dictionary<AnyHashable, AnyObject>>) {
if count + 1 < numberOfOperations {
count += 1
}
else {
print("All operations complete \(d.resultArray.count)")
print(d.resultArray)
}
}
func runOperationAndAddResult(queue:OperationQueue, result:ConcurrentResultData<Dictionary<AnyHashable, AnyObject>> ) {
queue.addOperation {
let id = UUID().uuidString
print("\(id) running")
let delay:Int = Int(arc4random_uniform(2) + 1)
for _ in 0..<delay {
sleep(1)
}
let dict:[Dictionary<AnyHashable, AnyObject>] = [[ "uuid" : NSString(string: id), "delay" : NSString(string:"\(delay)") ]]
result.appendAll(array:dict)
DispatchQueue.main.async {
print("\(id) complete")
operationCompleted(d:result)
}
}
}
let q = OperationQueue()
let d = ConcurrentResultData<Dictionary<AnyHashable, AnyObject>>()
for _ in 0..<10 {
runOperationAndAddResult(queue: q, result: d)
}
I had the same problem using queues in background. The synchronization is not working all the time in queues with "background" (low) priority.
One fix I found was to use semaphores instead of "obj_sync":
static private var syncSemaphores: [String: DispatchSemaphore] = [:]
static func synced(_ lock: String, closure: () -> ()) {
//get the semaphore or create it
var semaphore = syncSemaphores[lock]
if semaphore == nil {
semaphore = DispatchSemaphore(value: 1)
syncSemaphores[lock] = semaphore
}
//lock semaphore
semaphore!.wait()
//execute closure
closure()
//unlock semaphore
semaphore!.signal()
}
The function idea comes from What is the Swift equivalent to Objective-C's "#synchronized"?, an answer of #bryan-mclemore.
I was re-reading this post here: https://stackoverflow.com/a/24473888/1828637
And got concerned about if I did things correctly. This is how I do unloading:
So I set up some stuff per window. And unload them on shutdown. (i dont unload on window close, i havent found a need to yet, as when it closes, everything i added to it goes with with the close [such as my mutation observers]).
All code below is theoretical, the mutation stuff is example, so there might be typos or bugs in it. I was wondering if the idea behind it is appropriate:
var unloadersOnShutdown = [];
var unloadersOnClose = [];
function startup() {
let DOMWindows = Services.wm.getEnumerator(null);
while (DOMWindows.hasMoreElements()) {
let aDOMWindow = DOMWindows.getNext();
var worker = new winWorker(aDOMWindow);
unloadersOnShutdown.push({DOMWindow: aDOMWindow, fn: worker.destroy});
}
}
function shutdown() {
Array.forEach.call(unloadersOnShutdown, function(obj) {
//should probably test if obj.DOMWindow exists/is open, but just put it in try-ctach
try {
obj.fn();
} catch(ex) {
//window was probably closed
console.warn('on shutdown unlaoder:', ex);
}
});
}
function winWorker(aDOMWindow) {
this.DOMWindow = aDOMWindow;
this.init();
}
winWorker.prototype = {
init: function() {
this.gMutationObserver = new this.DOMWindow.MutationObserver(gMutationFunc.bind(this));
this.myElement = this.DOMWindow.querySelector('#myXulEl');
this.gMutationObserver.observe(this.myElement, gMutationConfig);
if (this.DOMWindow.gBrowser && this.DOMWindow.gBrowser.tabContainer) {
this.onTabSelectBinded = this.onTabSelect.bind(this);
this.gBrowser.tabContainer.addEventListener('TabSelect', this.onTabSelectBinded, false);
}
},
destroy: function() {
this.gMutationObserver.disconnect();
if (this.onTabSelectBinded) {
this.gBrowser.tabContainer.removeEventListener('TabSelect', this.onTabSelectBinded, false);
}
},
onTabSelect: function() {
console.log('tab selected = ', thisDOMWindow.gBrowser.selectedTab);
}
};
var windowListener = {
onOpenWindow: function (aXULWindow) {},
onCloseWindow: function (aXULWindow) {
var DOMWindow = aXULWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowInternal || Ci.nsIDOMWindow);
for (var i=0; i<unloadersOnClose.length; i++) {
if (unloadersOnClose.DOMWindow == DOMWindow) {
try {
unloadersOnClose.fn();
} catch(ex) {
console.warn('on close unloader:', ex);
}
unloadersOnClose.splice(i, 1);
i--;
}
}
},
onWindowTitleChange: function (aXULWindow, aNewTitle) {},
}
I think one problem is me not using weak references with DOMWindows but I'm not sure.
The idea around unloaders in general seems to be OK, but very limited (to windows only).
The implementation is lacking. E.g. there is a big, fat bug:
unloadersOnShutdown.push({DOMWindow: aDOMWindow, fn: worker.destroy});
// and
obj.fn();
// or
unloadersOnClose.fn();
This will call winWorker.prototype.destroy with the wrong this.
The i++/i-- loop also looks, um... "interesting"?!
Also, keep in mind that there can be subtle leaks, so you should mind and test for Zombie compartments.
Not only can a window leak parts of your add-on (e.g. bootstrap.js) but it is also possible to leak closed windows by keeping references in your add-on. And of course, it's not just windows you need to care about, but also e.g. observers, other types of (XPCOM) listeners etc.
I think I've gotten the most simplest scenario built. I just want to pass it by everyone for a sanity check. Here's the idea:
GetErrorCodes.cfm does the following:
<cfscript>
response = new ErrorCodes().WhereXXX(); // ACF or Railo, doesn't matter
</cfscript>
ErrorCodes.cfc:
function WhereXXX() {
return new sproc().exec('app.GetErrorCodes'); // All my functions will do this instead of executing the sproc themselves.
}
sproc.cfc:
component {
function exec(procedure) {
local.result = {};
if (server.ColdFusion.productname == 'Railo') {
return new Railo().exec(arguments.procedure); // Has to be outside of sproc.cfc because ColdFusion throws a syntax error otherwise.
}
local.svc = new storedProc();
local.svc.setProcedure(arguments.procedure);
local.svc.addProcResult(name='qry');
try {
local.obj = local.svc.execute();
local.result.Prefix = local.obj.getPrefix();
local.result.qry = local.obj.getProcResultSets().qry;
} catch(any Exception) {
request.msg = Exception.Detail;
}
return local.result;
}
Railo.cfc:
component {
function exec(procedure) {
local.result = {};
try {
storedproc procedure=arguments.procedure result="local.result.Prefix" returncode="yes" {
procresult name="local.result.qry";
}
} catch(any Exception) {
request.msg = Exception.Message;
}
return local.result;
}
}
So I've been working on this all day, but tell me, is this a sane way to keep the source code the same if it's to be run on either a ColdFusion server or a Railo server?
Um... just use <cfstoredproc> instead of trying to use two different CFScript approaches that are mutually exclusive to each other of the CFML platforms.