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I am attempting to build a system in delphi that allows users to use Google Maps. It all works fine, but i'm noticing that every time a new TWebBrowser object is created and the javascript that handles Google Maps is loaded, a number of new Threads is generated.
My problem is that even once the webbrowser is destroyed (and it is definately destroyed) the created threads persist. I'm designing this program to have long running times and the opening and closing of google maps to happen many times and as such, after a while, so many threads have been generated and not terminated that the program slows down dramatically.
Is there any way to Destroy these threads myself, or am I doing something wrong which is causing the threads to persist?
I am basing my program off of the following code:
const
HTMLStr: AnsiString =
'<html> '+
'<head> '+
'<meta name="viewport" content="initial-scale=1.0, user-scalable=yes" /> '+
'<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=true"> </script> '+
'<script type="text/javascript"> '+
''+
''+
' var geocoder; '+
' var map; '+
' var trafficLayer;'+
' var bikeLayer;'+
' var markersArray = [];'+
''+
''+
' function initialize() { '+
' geocoder = new google.maps.Geocoder();'+
' var latlng = new google.maps.LatLng(40.714776,-74.019213); '+
' var myOptions = { '+
' zoom: 13, '+
' center: latlng, '+
' mapTypeId: google.maps.MapTypeId.ROADMAP '+
' }; '+
' map = new google.maps.Map(document.getElementById("map_canvas"), myOptions); '+
' trafficLayer = new google.maps.TrafficLayer();'+
' bikeLayer = new google.maps.BicyclingLayer();'+
' map.set("streetViewControl", false);'+
' } '+
''+
''+
' function codeAddress(address) { '+
' if (geocoder) {'+
' geocoder.geocode( { address: address}, function(results, status) { '+
' if (status == google.maps.GeocoderStatus.OK) {'+
' map.setCenter(results[0].geometry.location);'+
' PutMarker(results[0].geometry.location.lat(), results[0].geometry.location.lng(), results[0].geometry.location.lat()+","+results[0].geometry.location.lng());'+
' } else {'+
' alert("Geocode was not successful for the following reason: " + status);'+
' }'+
' });'+
' }'+
' }'+
''+
''+
' function GotoLatLng(Lat, Lang) { '+
' var latlng = new google.maps.LatLng(Lat,Lang);'+
' map.setCenter(latlng);'+
' PutMarker(Lat, Lang, Lat+","+Lang);'+
' }'+
''+
''+
'function ClearMarkers() { '+
' if (markersArray) { '+
' for (i in markersArray) { '+
' markersArray[i].setMap(null); '+
' } '+
' } '+
'} '+
''+
' function PutMarker(Lat, Lang, Msg) { '+
' var latlng = new google.maps.LatLng(Lat,Lang);'+
' var marker = new google.maps.Marker({'+
' position: latlng, '+
' map: map,'+
' title: Msg+" ("+Lat+","+Lang+")"'+
' });'+
' markersArray.push(marker); '+
' }'+
''+
''+
' function TrafficOn() { trafficLayer.setMap(map); }'+
''+
' function TrafficOff() { trafficLayer.setMap(null); }'+
''+''+
' function BicyclingOn() { bikeLayer.setMap(map); }'+
''+
' function BicyclingOff(){ bikeLayer.setMap(null);}'+
''+
' function StreetViewOn() { map.set("streetViewControl", true); }'+
''+
' function StreetViewOff() { map.set("streetViewControl", false); }'+
''+
''+'</script> '+
'</head> '+
'<body onload="initialize()"> '+
' <div id="map_canvas" style="width:100%; height:100%"></div> '+
'</body> '+
'</html> ';
procedure TfrmMain.FormCreate(Sender: TObject);
var
aStream : TMemoryStream;
begin
WebBrowser1.Navigate('about:blank');
if Assigned(WebBrowser1.Document) then
begin
aStream := TMemoryStream.Create;
try
aStream.WriteBuffer(Pointer(HTMLStr)^, Length(HTMLStr));
//aStream.Write(HTMLStr[1], Length(HTMLStr));
aStream.Seek(0, soFromBeginning);
(WebBrowser1.Document as IPersistStreamInit).Load(TStreamAdapter.Create(aStream));
finally
aStream.Free;
end;
HTMLWindow2 := (WebBrowser1.Document as IHTMLDocument2).parentWindow;
end;
end;
procedure TfrmMain.ButtonGotoLocationClick(Sender: TObject);
begin
HTMLWindow2.execScript(Format('GotoLatLng(%s,%s)',[Latitude.Text,Longitude.Text]), 'JavaScript');
end;
procedure TfrmMain.ButtonClearMarkersClick(Sender: TObject);
begin
HTMLWindow2.execScript('ClearMarkers()', 'JavaScript')
end;
procedure TfrmMain.ButtonGotoAddressClick(Sender: TObject);
var
address : string;
begin
address := MemoAddress.Lines.Text;
address := StringReplace(StringReplace(Trim(address), #13, ' ', [rfReplaceAll]), #10, ' ' , [rfReplaceAll]);
HTMLWindow2.execScript(Format('codeAddress(%s)',[QuotedStr(address)]), 'JavaScript');
end;
procedure TfrmMain.CheckBoxStreeViewClick(Sender: TObject);
begin
if CheckBoxStreeView.Checked then
HTMLWindow2.execScript('StreetViewOn()', 'JavaScript')
else
HTMLWindow2.execScript('StreetViewOff()', 'JavaScript');
end;
procedure TfrmMain.CheckBoxBicyclingClick(Sender: TObject);
begin
if CheckBoxBicycling.Checked then
HTMLWindow2.execScript('BicyclingOn()', 'JavaScript')
else
HTMLWindow2.execScript('BicyclingOff()', 'JavaScript');
end;
procedure TfrmMain.CheckBoxTrafficClick(Sender: TObject);
begin
if CheckBoxTraffic.Checked then
HTMLWindow2.execScript('TrafficOn()', 'JavaScript')
else
HTMLWindow2.execScript('TrafficOff()', 'JavaScript');
end;
end.
Program uses a basic destructor that sets the HTMLWindow to navigate to about:blank. Thanks in advance
908
This does not answer this question, it only simplifies the problem to be simulated.
See how many threads is running after each button click. It uses the Simple Google Maps example, so the problem is not even in your javascript part.
Unit1 - contains main form, where is just a button with OnClick event handler
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, PsAPI, TlHelp32, Unit2;
type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
function GetThreadCount(const APID: Cardinal): Integer;
var
NextProc: Boolean;
ProcHandle: THandle;
ThreadEntry: TThreadEntry32;
begin
Result := 0;
ProcHandle := CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, 0);
if (ProcHandle <> INVALID_HANDLE_VALUE) then
try
ThreadEntry.dwSize := SizeOf(ThreadEntry);
NextProc := Thread32First(ProcHandle, ThreadEntry);
while NextProc do
begin
if ThreadEntry.th32OwnerProcessID = APID then
Inc(Result);
NextProc := Thread32Next(ProcHandle, ThreadEntry);
end;
finally
CloseHandle(ProcHandle);
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
ModalForm: TForm2;
begin
ModalForm := TForm2.Create(nil);
try
ModalForm.ShowModal;
finally
ModalForm.Free;
end;
ShowMessage('Thread count: ' +
IntToStr(GetThreadCount(GetCurrentProcessId)));
end;
end.
Unit2 - contains form with the TWebBrowser on it and the form's OnCreate event handler
unit Unit2;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, OleCtrls, SHDocVw, ActiveX;
type
TForm2 = class(TForm)
WebBrowser1: TWebBrowser;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form2: TForm2;
implementation
{$R *.dfm}
const
HTMLString: AnsiString =
'<!DOCTYPE html>' +
'<html>' +
' <head>' +
' <title>Google Maps JavaScript API v3 Example: Map Simple</title>' +
' <meta name="viewport"' +
' content="width=device-width, initial-scale=1.0, user-scalable=no">' +
' <meta charset="UTF-8">' +
' <style type="text/css">' +
' html, body, #map_canvas {' +
' margin: 0;' +
' padding: 0;' +
' height: 100%;' +
' }' +
' </style>' +
' <script type="text/javascript"' +
' src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>' +
' <script type="text/javascript">' +
' var map;' +
' function initialize() {' +
' var myOptions = {' +
' zoom: 8,' +
' center: new google.maps.LatLng(-34.397, 150.644),' +
' mapTypeId: google.maps.MapTypeId.ROADMAP' +
' };' +
' map = new google.maps.Map(document.getElementById(''map_canvas''),' +
' myOptions);' +
' }' +
' google.maps.event.addDomListener(window, ''load'', initialize);' +
' </script>' +
' </head>' +
' <body>' +
' <div id="map_canvas"></div>' +
' </body>' +
'</html>';
procedure TForm2.FormCreate(Sender: TObject);
var
HTMLStream: TMemoryStream;
begin
WebBrowser1.Navigate('about:blank');
if Assigned(WebBrowser1.Document) then
begin
HTMLStream := TMemoryStream.Create;
try
HTMLStream.WriteBuffer(Pointer(HTMLString)^, Length(HTMLString));
HTMLStream.Seek(0, soFromBeginning);
(WebBrowser1.Document as IPersistStreamInit).Load(TStreamAdapter.Create(HTMLStream));
finally
HTMLStream.Free;
end;
end;
end;
end.
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