I am using OTL for the first time and I was trying to use the Async/Await abstraction.
Now, I created a small program just to see what will happen. It's just a button and it calls this procedure.
procedure TForm2.Button1Click(Sender: TObject);
var i : integer;
begin
Button1.enabled := false; //Only for second try
for i := 0 to 100 do
begin
Async(
procedure begin
sleep(5000);
end).
Await(
procedure begin
//First Try - Button1.Enabled := true;
//Second Try - showmessage('finished')
end
);
Button1.enabled := true; //Only for the second try.
end;
end;
First Try
For this it works fine the first time, disable the button, sleep for the asyncs and then enable it back.
But the second time I click the button, it is disabled but never gets enabled again.
Second Try
This time I wanted to show a message x100 times and it works the first time aswell, but when I call the procedure again I get the following error TOminCommunicationEndpoint.Send: Queue is full
Can someone who has used this library explain to me, why am I getting this error? And if it is related to the problem with the first try?
It seems you are hitting an internal limitation of OTL.
Each call to Async-Await starts a new thread and returns immediately. When the loop is done you end up with 100 threads, each waiting 5 seconds before executing the Await code.
AFAIK, there is a limitation of 60 concurrent threads in OTL when using the threadpool.
Related
I am using a TEdit to allow the user to enter a number, e.g. 10.
I convert the TEdit.Text to an integer and a calculation procedure is called.
In this calc procedure, a check was built-in to make sure no numbers below 10 are processed.
Currently I use the OnChange event. Suppose the user wants to change '10' into e.g.'50'. But as soon as the '10' is deleted or the '5' (to be followed by the 0) is typed, I trigger my warning that the minimum number is 10. I.e. the program won't wait until I have fully typed the 5 and 0.
I tried OnEnter, OnClick, OnExit, but I seem not to overcome this problem. The only solution is to add a separate button that will trigger the calculation with the new number. It works, but can I do without the button?
Use a timer for a delayed check, e.g.:
procedure TForm1.Edit1Change(Sender: TObject);
begin
// reset the timer
Timer1.Enabled := false;
Timer1.Enabled := true;
end;
procedure TForm1.Timer1Timer(Sender: TObject);
begin
Timer1.Enabled := false;
// do your check here
end;
Setting the timer to 500 ms should be fine for most users.
And as David suggested in the comments to the question: Do not show an error dialog, use something less intrusive instead, e.g. an error message in a label near the edit or change the background color. And also: Do not prevent the focus to be moved away from that control and do not play a sound, that's also very annoying.
For our in house software we set the background of a control to yellow if there is an error and display the error message of the first such error in the status bar and also as a hint of the control. If you do that, you probably don't even need to have the delay.
Thanks, for your help. I tried the timer option, but could not get that to work. I now have this code, which works (almost - see below), but requires the used to always type a CR:
procedure Calculate;
begin
// this is my calculation procedure
ShowMessage('calculation running correctly');
end;
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
var
N : integer;
begin
if Key = #13 then
begin
N := StrtoInt(Edit1.Text);
if N<10 then ShowMessage('<10!') else
if N>100 then ShowMessage('>100!') else Calculate;
end;
end;
I used the ShowMessage() here only to see if the sample code worked. In the real program I have left that out, as you all suggested.
I also included the 'turn yellow on wrong entry' (thanks David). The only issue is that if the user runs this I get a beep from my computer. I can't see what went wrong. But what is causing the beep?
please tell me: how to know if TEvent is Signaled or not?
Click on STOP-button = SetEvent(Events[1]);
I am trying to unzip an archive and if STOP-button is pressed then a tread must be terminated and Unzippping must be aborted.
My code:
procedure TForm2.ZipForge1OverallProgress(Sender: TObject; Progress: Double;
Operation: TZFProcessOperation; ProgressPhase: TZFProgressPhase;
var Cancel: Boolean);
begin
if Events[1]<>null then
begin
ThreadUpdating.Terminate;
Abort;
end else
form2.Update_ProgressBar.Position := Trunc(Progress);
end;
But if I press STOP-button(SetEvent(Events[1])) nothing happens.
PS: I am using WaitForMultipleObjects(Event[1],Event[2]) in a thread. Event [1] is being used as a signal of STOP in two parts: in ZipForge1OverallProgress and WaitForMultipleObjects.
Call WaitForMultipleObjects, but do it properly. You haven't shown that code, and the code you have shown doesn't look right anyway.
First, it looks like you're trying to check whether the Events[1] element is a null pointer. Null pointers in Delphi are spelled nil, not null; the latter is a function that returns a null Variant value (but since Variant is convertible to lots of other types, the compiler probably doesn't alert you that your code is wrong). Next, it looks as though the event you're handling has a Cancel parameter that you can set to notify the caller that it should stop what it's doing, but instead of just setting that, you're throwing an EAbort exception.
If the progress event you show here is really running in a separate thread, then it must not modify property of VCL objects like TProgressBar. You need to use Synchronize to make sure VCL operations only occur in the VCL thread.
As I said, you need to call WaitForMultipleObjects property. That means passing it four parameters, for one thing. You appear to have an array with at least two handles in it, so call it like this:
var
Ret: DWord;
Ret := WaitForMultipleObjects(2, #Events[1], False, Timeout);
case Ret of
Wait_Object_0: begin
// Events[1] is signaled
end;
Wait_Object_0 + 1: begin
// Events[2] is signaled
end;
Wait_Timeout: begin
// Neither is signaled. Do some more work, or go back to waiting.
end;
Wait_Failed: begin
RaiseLastOSError;
end;
end;
If all you want to do is check whether the handle is signaled, but you don't want to wait for it to become signaled if it isn't already, then use a timeout value of zero.
'if Events[1]<>null then begin' is this pseudocode? Doesn't lok like it - looks more like real Delphi to me:) If so, you are just checking to see if the Event object is assigned, rather than signaled.
If you want to poll the stop event in your OverallProgress handler, you need to call WaitForSingleObject() with a timeout of 0.
Can you not just check a 'stop' boolean in your handler? This would be much quicker than a kernel call. You may need the Event as well so that the WFMO call at the top of the thread gets signaled when an abort/terminate is needed or you might get away with signaling some other event in the WFMO array by always checking for stop:
TmyThread = class(TThread)
..
public
stopRequested:boolean;
procedure stop;
..
end;
procedure TmyThread.stop;
begin
stopRequested:=true;
someEventInWFMOarray.signal;
end;
procedure TmyThread.execute;
begin;
while true do
begin
waitForMultipeObjects();
if stopRequested then exit;
work;
end;
end;
TForm2.ZipForge1OverallProgress(sender:TObject,......)
begin
cancel:=TmyThread(Sender).stopRequested;
if cancel then exit;
doStuff;
end;
I have never asked questions in any community as I always solved problems by myself or could find them online. But with this one I came to dead end and need Help!
To make it very clear – I converted a simple app, found elsewhere to make it use a Tthread object.
The idea is simple – the app checks online using webservice, through THTTPRIO component, weather and put the results in Memo1 lines.
Clicking on Button1 we get it done in standard way – using THTTPRIO put on the Form1 (it's called here htt as in original app) and using main and only thread.
procedure TForm1.Button1Click(Sender: TObject);
var
wf:WeatherForecasts;
res:ArrayOfWeatherData;
i:integer;
begin
wf:=(htt as WeatherForecastSoap).GetWeatherByPlaceName(edit1.Text);
if wf.PlaceName<> '' then
res:=wf.Details;
memo1.Lines.Add('The min and max temps in Fahrenheit is:');
memo1.Lines.Add(' ');
for i:= 0 to high(res) do
begin
memo1.Lines.Add(res[i].Day+' - '+ ' Max Temp. Fahr: '+res[i].MaxTemperatureF+' - '+'Min Temp Fahr: '+res[i].MinTemperatureF);
end
end;
Clicking on Button2 – we use class TThread
procedure TForm1.Button2Click(Sender: TObject);
var WFThread:WeatherThread;
begin
WFThread := WeatherThread.Create (True);
WFThread.FreeOnTerminate := True;
WFThread.Place := Edit1.Text;
WFThread.Resume;
end;
In Execute procedure in WeatherThread1 unit I put this code:
procedure WeatherThread.Execute;
begin
{ Place thread code here }
GetForecast;
Synchronize (ShowWeather);
end;
...and the GetForecast code:
procedure WeatherThread.GetForecast;
var
HTTPRIO: THTTPRIO;
wf:WeatherForecasts;
res:ArrayOfWeatherData;
i:integer;
begin
HTTPRIO := THTTPRIO.Create(nil);
HTTPRIO.URL := 'http://www.webservicex.net/WeatherForecast.asmx';
HTTPRIO.WSDLLocation := 'http://www.webservicex.net/WeatherForecast.asmx?WSDL';
HTTPRIO.Service := 'WeatherForecast';
HTTPRIO.Port := 'WeatherForecastSoap';
wf:=(HTTPRIO as WeatherForecastSoap).GetWeatherByPlaceName(Place);
if Lines=nil then Lines:=TStringList.Create;
if wf.PlaceName<> '' then
res:=wf.Details;
Lines.Clear;
for i:= 0 to high(res) do
begin
Lines.Add(res[i].Day+' - '+ ' Max Temp. Fahr: '+res[i].MaxTemperatureF+' - '+'Min Temp Fahr: '+res[i].MinTemperatureF);
end;
end;
Procedure ShowWeather shows results in Form1.Memo1.
And now there is a problem: In main thread, clicking Button1, everything works fine. But of course when HTTPRIO component communicates – it freezes the form.
With Button2 I put the code in separate thread but it does NOT WANT TO WORK! Something strange happens. When I start application – and click Button2, there is an error when using HTTPRIO component. But it works for a while when I click FIRST Button1 and AFTER THAT Button2 (but it works for a while, 5-7 clicks only).
I suppose I do something wrong but cannot figure out where the problem is and how to solve it. It looks like the code in threaded unit is not thread-safe, but it should be. Please help how to make HTTPRIO work in a thread!!!
You can find zipped full code here.
When I run your code in Delphi 2007, madExcept shows an exception CoInitialize has not been called.
After adding the call to CoInitialize in the execute method, the webservice gets called without problems.
Possible fix
procedure TWeatherThread.Execute;
begin
CoInitialize(nil);
try
...
finally
CoUninitialize;
end;
end;
A long shot, but I'm missing calls to Synchronize here:
You should never update your GUI directly from your thread code.
You should embed those calls inside a method, and call that method using the TThread.Synchronize method for this.
Delphi about has a nice demo on this.
Since Delphi 4, it includes a demo called sortthds.pas in the ...\demos\threads subdirectory that shows the same.
--jeroen
You may be clouding the issue by doing the dynamic RIO creation (RIO objects have a strange lifetime) and threading together, and comparing that outcome to the straightforward Button1. I'd make another button that calls GetForecast without threads. See if that works. If it bombs, then your problem isn't threading.
how can i pause and resume in application while working with loops
i can put some sleep(xxx) at begininsg of my loop to pause ,but i want pause when ever i want and resume when i ever i need
any ideas ?
thanks in advance
ok here is alittle more explanation
for i:=0 to 100 do
begin
if button1.clicked then pause //stop the operation and wait for resume button
if button2.clicked then resume //resume the operations
end;
edit2 :
ok guys i will tell an example well take any checker for suppose proxy checker ,i have a bunch of proxies loaded in my tlistviwe i am checking them all ,by using lop for i:=0 to listview.items.count do ......
i want to pause my checking operation when ever i want and resume when ever i need
am i clear or still i have to explain some ? :S
regards
You need a boolean flag that will indicate whether it's safe to continue looping. If something happens that makes it so you need to pause, it should set the variable to false. This means that, unless you're working with multiple threads, whatever sets this flag will have to be checked inside the loop somewhere. Then at the top (or the bottom) of your loop, check to see if this variable is true and pause otherwise.
Here's the basic idea, in the context of your explanation:
procedure TForm1.DoLoop;
begin
FCanContinue := true;
for i:=0 to 100 do
begin
//do whatever
Application.ProcessMessages; //allow the UI to respond to button clicks
if not FCanContinue then Pause;
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
FCanContinue := false;
end;
procedure TForm2.Button1Click(Sender: TObject);
begin
FCanContinue := true;
Resume;
end;
This is a very simplistic implementation. What you really should do if you have a long-running task that you need to be able to pause and resume on command is put this in a separate thread and take a look at the TEvent class in SyncObjs.
OK, I don't understand what you are trying to do, but here is some pseudo code:
for i:=0 to 100 do
begin
if button1.clicked then
begin
while not button2.clicked do
sleep(50);
end;
end;
Check if a key is pressed?
Actually i am using the AsyncCalls library to execute an Query asynchronously in this way.
while AsyncMultiSync([RunQuery], True, 10) = WAIT_TIMEOUT do
begin
FrmProgress.refresh; //Update the ellapsed time in a popup form
Application.ProcessMessages;
end;
and everything works ok.
Now i want to do the same for load the query in a grid.
so i tried this
while LocalAsyncVclCall(#InitGrid, 10) = WAIT_TIMEOUT do
begin
FrmProgress.refresh;
Application.ProcessMessages;
end;
but obviously not compile because the type returned by LocalAsyncVclCall is IAsyncCall and not a Cardinal.
also i tried this, but not works because the initgrid procedure is executed but not asynchronously.
while not LocalAsyncVclCall(#InitGrid, 10).Finished do
begin
FrmProgress.refresh;
//Application.ProcessMessages;
end;
How i can use LocalAsyncVclCall or another function to execute an VCL code asynchronously .
i want something like this.
while ExecuteMyVCLProcedure(#InitGrid) = WAIT_TIMEOUT do
begin
FrmProgress.refresh;
//Application.ProcessMessages;
end;
UPDATE
The InitGrid procedure goes here, the TcxGrid does not provide any event to show the progress of the data load. because that i want to execute this procedure asynchronously.
procedure InitGrid;
begin
cxGrid1DBTableView1.BeginUpdate;
try
cxGrid1DBTableView1.DataController.DataSource:=DataSource1;//in this point assign the query previously executed to the grid.
cxGrid1DBTableView1.ClearItems;
cxGrid1DBTableView1.DataController.CreateAllItems;
for ColIndex:=0 to cxGrid1DBTableView1.ColumnCount-1 do
cxGrid1DBTableView1.Columns[ColIndex].Options.Editing:=False;
finally
cxGrid1DBTableView1.EndUpdate;
end;
end;
Thanks in advance.
UPDATE The InitGrid procedure goes
here, the TcxGrid does not provide any
event to show the progress of the data
load. because that i want to execute
this procedure asynchronously
You can't populate the cxGrid in a different VCL thread because there is only one VCL Thread, the MainThread. Calling LocalAsyncVclCall from the MainThread does nothing else than executing the given function in the thread that calls LocalAsyncVclCall. So it wouldn't do anything different than calling the InitGrid() function in the same thread where your ProcessMessages() call is. Hence ProcessMessages() would be called after the data was loaded into the cxGird what is not what you want.
All the *VclCall() functions are intended to be executed from a different thread than the MainThread.
Without changing the cxGrid's code to support a "progress event" you are out of luck with your attempt.
Use PostMessage to send a custom windows message to FrmProgress.
e.g
WM_PopulateGrid = WM_USER + 1;
procedure WMPopulateGrid(var msg: TMessage); message WM_PopulateGrid;
begin
//load records into the grid.
//You maybe can use a global variable to pass the records from RunQuery
....
end;