Delphi Thread Pool Example Using AsyncCalls 异步调用Word文档下载推荐.docx

Delphi Thread Pool Example Using AsyncCalls 异步调用Word文档下载推荐.docx

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Torepeatmygoal:

transformmysequential"

of500-2000+filesfromthenonthreadedapproachtoathreadedone.Ishouldnothave500threadsrunningatonetime,thuswouldliketouseathreadpool.Athreadpoolisaqueue-likeclassfeedinganumberofrunningthreadswiththenexttaskfromthequeue.

Thefirst（verybasic）attemptwasmadebysimplyextendingtheTThreadclassandimplementingtheExecutemethod（mythreadedstringparser）.

SinceDelphidoesnothaveathreadpoolclassimplementedoutofthebox,inmysecondattemptI'

vetriedusingOmniThreadLibrarybyPrimozGabrijelcic.

OTLisfantastic,haszillionwaystorunataskinabackground,awaytogoifyouwanttohave"

fire-and-forget"

approachtohandingthreadedexecutionofpiecesofyourcode.

AsyncCallsbyAndreasHausladen

Note:

whatfollowswouldbemoreeasytofollowifyoufirstdownloadthesourcecode.

WhileexploringmorewaystohavesomeofmyfunctionsexecutedinathreadedmannerI'

vedecidedtoalsotrythe"

AsyncCalls.pas"

unitdevelopedbyAndreasHausladen.Andy'

sAsyncCalls–AsynchronousfunctioncallsunitisanotherlibraryaDelphidevelopercanusetoeasethepainofimplementingthreadedapproachtoexecutingsomecode.

FromAndy'

sblog:

WithAsyncCallsyoucanexecutemultiplefunctionsatthesametimeandsynchronizethemateverypointinthefunctionormethodthatstartedthem....TheAsyncCallsunitoffersavarietyoffunctionprototypestocallasynchronousfunctions....Itimplementsathreadpool!

Theinstallationissupereasy:

justuseasynccallsfromanyofyourunitsandyouhaveinstantaccesstothingslike"

executeinaseparatethread,synchronizemainUI,waituntilfinished"

.

Besidethefreetouse（MPLlicense）AsyncCalls,AndyalsofrequentlypublisheshisownfixesfortheDelphiIDElike"

DelphiSpeedUp"

and"

DDevExtensions"

I'

msureyou'

veheardof（ifnotusingalready）.

AsyncCallsInAction

Whilethere'

sonlyoneunittoincludeinyourapplication,theasynccalls.pasprovidesmorewaysonecanexecuteafunctioninadifferentthreadanddothreadsynchronization.TakealookatthesourcecodeandtheincludedHTMLhelpfiletogetfamiliarwiththebasicsofasynccalls.

Inessence,allAsyncCallfunctionsreturnanIAsyncCallinterfacethatallowstosynchronizethefunctions.IAsnycCallexposesthefollowingmethods:

//v2.98ofasynccalls.pas

IAsyncCall=interface

//waitsuntilthefunctionisfinishedandreturnsthereturnvalue

functionSync:

Integer;

//returnsTruewhentheasynchronfunctionisfinished

functionFinished:

Boolean;

//returnstheasynchronfunction'

sreturnvalue,whenFinishedisTRUE

functionReturnValue:

//tellsAsyncCallsthattheassignedfunctionmustnotbeexecutedinthecurrentthrea

procedureForceDifferentThread;

end;

AsIfancygenericsandanonymousmethodsI'

mhappythatthere'

saTAsyncCallsclassnicelywrappingcallstomyfunctionsIwanttobeexecutedinathreadedmanner.

Here'

sanexamplecalltoamethodexpectingtwointegerparameters（returninganIAsyncCall）:

TAsyncCalls.Invoke（AsyncMethod,i,Random（500））;

TheAsyncMethodisamethodofaclassinstance（forexample:

apublicmethodofaform）,andisimplementedas:

functionTAsyncCallsForm.AsyncMethod（taskNr,sleepTime:

integer）:

integer;

begin

result:

=sleepTime;

Sleep（sleepTime）;

TAsyncCalls.VCLInvoke（

procedure

begin

Log（Format（'

done>

nr:

%d/tasks:

%d/slept:

%d'

[tasknr,asyncHelper.TaskCount,sleepTime]））;

end）;

Again,I'

musingtheSleepproceduretomimicsomeworkloadtobedoneinmyfunctionexecutedinaseparatethread.

TheTAsyncCalls.VCLInvokeisawaytodosynchronizationwithyourmainthread（application'

smainthread-yourapplicationuserinterface）.VCLInvokereturnsimmediately.Theanonymousmethodwillbeexecutedinthemainthread.There'

salsoVCLSyncwhichreturnswhentheanonymousmethodwascalledinthemainthread.

ThreadPoolinAsyncCalls

Asexplainedintheexamples/helpdocument（AsyncCallsInternals-Threadpoolandwaiting-queue）:

Anexecutionrequestisaddedtothewaiting-queuewhenanasync.functionisstarted...Ifthemaximumthreadnumberisalreadyreachedtherequestremainsinthewaiting-queue.Otherwiseanewthreadisaddedtothethreadpool.

Backtomy"

task:

whenfeeding（inaforloop）