如何解决在阻塞主线程中使用TEvent和MsgWaitForMultipleObjects
我找到了雷米有趣的代码。 Delphi : How to create and use Thread locally?
是否可以这样做,以便我可以执行多个线程并等待它们全部完成,然后继续执行主线程?我这样尝试过,但没有成功...
procedure Requery(DataList: TStringList);
var
Event: TEvent;
H: THandle;
OpResult: array of Boolean;
i: Integer;
begin
Event := TEvent.Create;
try
SetLength(OpResult,DataList.Count);
for i:=0 to DataList.Count-1 do begin
TThread.CreateAnonymousThread(
procedure
begin
try
// run query in thread
OpResult[i]:=IsMyValueOK(DataList.Strings[i]);
finally
Event.SetEvent;
end;
end
).Start;
H := Event.Handle;
end;
while MsgWaitForMultipleObjects(1,H,False,INFINITE,QS_ALLINPUT) = (WAIT_OBJECT_0+1) do Application.ProcessMessages;
for i:=Low(OpResult) to High(OpResult) do begin
Memo1.Lines.Add('Value is: ' + BoolToStr(OpResult[i],True));
end;
finally
Event.Free;
end;
// Do next jobs with query
...
end;
解决方法
可以做到这一点,这样我就可以做多个线程并等待它们全部完成
是的。您只需要创建多个TEvent
对象,每个TThread
一个,然后将它们的所有Handle
存储在一个数组中以传递给MsgWaitForMultipleObjects()
:
procedure Requery(DataList: TStringList);
var
Events: array of TEvent;
H: array of THandle;
OpResult: array of Boolean;
i: Integer;
Ret,Count: DWORD;
// moved into a helper function so that the anonymous procedure
// can capture the correct Index...
procedure StartThread(Index: integer);
begin
Events[Index] := TEvent.Create;
TThread.CreateAnonymousThread(
procedure
begin
try
// run query in thread
OpResult[Index] := IsMyValueOK(DataList.Strings[Index]);
finally
Events[Index].SetEvent;
end;
end
).Start;
H[Index] := Events[Index].Handle;
end;
begin
if DataList.Count > 0 then
begin
SetLength(Events,DataList.Count);
SetLength(H,DataList.Count);
SetLength(OpResult,DataList.Count);
try
for i := 0 to DataList.Count-1 do begin
StartThread(i);
end;
Count := Length(H);
repeat
Ret := MsgWaitForMultipleObjects(Count,H[0],False,INFINITE,QS_ALLINPUT);
if Ret = WAIT_FAILED then RaiseLastOSError;
if Ret = (WAIT_OBJECT_0+Count) then
begin
Application.ProcessMessages;
Continue;
end;
for i := Integer(Ret-WAIT_OBJECT_0)+1 to High(H) do begin
H[i-1] := H[i];
end;
Dec(Count);
until Count = 0;
for i := Low(OpResult) to High(OpResult) do begin
Memo1.Lines.Add('Value is: ' + BoolToStr(OpResult[i],True));
end;
finally
for i := Low(Events) to High(Events) do begin
Events[i].Free;
end;
end;
end;
// Do next jobs with query
...
end;
话虽如此,您也可以摆脱TEvent
对象,而等待TThread.Handle
。线程的Handle
完全终止后,将发出信号等待操作。唯一的陷阱是TThread.CreateAnonymousThread()
创建了一个TThread
属性为FreeOnTerminate
的{{1}},因此您必须手动将其关闭:
True
无论哪种方式,请注意,procedure Requery(DataList: TStringList);
var
Threads: array of TThread;
H: array of THandle;
OpResult: array of Boolean;
i: Integer;
Ret,Count: DWORD;
// moved into a helper function so that the anonymous procedure
// can capture the correct Index...
procedure StartThread(Index: integer);
begin
Threads[Index] := TThread.CreateAnonymousThread(
procedure
begin
// run query in thread
OpResult[Index] := IsMyValueOK(DataList.Strings[Index]);
end
);
Threads[Index].FreeOnTerminate := False;
H[Index] := Threads[Index].Handle;
Threads[Index].Start;
end;
begin
try
SetLength(Threads,DataList.Count);
for i := 0 to DataList.Count-1 do begin
StartThread(i);
end;
Count := Length(H);
repeat
Ret := MsgWaitForMultipleObjects(Count,QS_ALLINPUT);
if Ret = WAIT_FAILED then RaiseLastOSError;
if Ret = (WAIT_OBJECT_0+Count) then
begin
Application.ProcessMessages;
Continue;
end;
for i := Integer(Ret-WAIT_OBJECT_0)+1 to High(H) do begin
H[i-1] := H[i];
end;
Dec(Count);
until Count = 0;
for i := Low(OpResult) to High(OpResult) do begin
Memo1.Lines.Add('Value is: ' + BoolToStr(OpResult[i],True));
end;
finally
for i := Low(Threads) to High(Threads) do begin
Threads[i].Free;
end;
end;
// Do next jobs with query
...
end;
仅限于一次等待最多63(MsgWaitForMultipleObjects()
[64]-1)个句柄。 WaitForMultipleObjects()
文档说明了如何解决该限制(如果需要)
要等待超过MAXIMUM_WAIT_OBJECTS个句柄,请使用以下方法之一:
- 创建一个线程以等待MAXIMUM_WAIT_OBJECTS句柄,然后等待该线程以及其他句柄。使用此技术将句柄分成MAXIMUM_WAIT_OBJECTS组。
- 调用RegisterWaitForSingleObject以等待每个句柄。线程池中的等待线程等待MAXIMUM_WAIT_OBJECTS注册的对象,并在该对象发出信号或超时间隔到期后分配工作线程。
或者,您可以简单地批量处理列表,一次说不超过50至60个项目。
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