WIN32下DELPHI中的多线程【同步2】(五)

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线xian程cheng同tong步bu2

上shang一yi文wen中zhong曾zeng经jing介jie绍shao了le线xian程cheng同tong步bu的de一yi些xie方fang法fa，其qi实shi完wan成cheng同tong步bu还huan有you很hen多duo很hen多duo的de办ban法fa，这zhe里li最zui后hou介jie绍shao一yi种zhong方fang式shi－－信xin号hao量liang内nei核gai对dui象xiang。并bing借jie此ci来lai回hui顾gu线xian程cheng同tong步bu。

在zai谈tan论lun信xin号hao量liang之zhi前qian，我wo想xiang先xian谈tan论lun另ling外wai一yi种zhong方fang式shi，一yi种zhong你ni最zui好hao不bu要yao使shi用yong的de方fang式shi。假jia设she你ni有you一yi个ge公gong共gong内nei存cun区qu域yu，你ni不bu希xi望wang一yi个ge线xian程cheng在zai完wan成cheng一yi个ge操cao作zuo之zhi前qian另ling外wai一yi个ge线xian程cheng对dui他ta进jin行xing另ling外wai的de操cao作zuo。抛pao开kai前qian面mian所suo有you的de知zhi识shi，我wo们men可ke以yi使shi用yong这zhe样yang一yi种zhong办ban法fa，一yi种zhong所suo有you人ren都dou会hui想xiang到dao的de办ban法fa。

程cheng序xu中zhong设she置zhi一yi个ge布bu尔er类lei型xing的de公gong共gong变bian量liangFLAG，此ci公gong共gong变bian量liang唯wei一yi的de最zui用yong是shi决jue定ding线xian程cheng是shi否fou是shi否fou可ke以yi操cao作zuo公gong共gong内nei存cun区qu域yu。如ru果guo是shiTRUE则ze允yuan许xu操cao作zuo，如ru果guo是shiFALSE则ze禁jin止zhi操cao作zuo。在zai线xian程cheng将jiang要yao执zhi行xing对dui共gong享xiang内nei存cun的de操cao作zuo时shi，反fan复fu判pan断duan此ci变bian量liang，类lei似si一yi个ge死si循xun环huan，直zhi到daoFLAG变bian为weiTRUE。思si路lu很hen简jian单dan，实shi现xian起qi来lai也ye比bi前qian面mian介jie绍shao的de那na些xie方fang法fa更geng容rong易yi，在zai某mou种zhong意yi义yi上shang说shuo，它ta也ye是shi有you效xiao的de。但dan文wen章zhang前qian面mian曾zeng经jing说shuo过guo，最zui好hao不bu用yong使shi用yong这zhe种zhong方fang式shi，为wei什shen么me？回hui顾gu线xian程cheng的de工gong作zuo状zhuang态tai，我wo们men基ji本ben可ke以yi这zhe样yang划hua分fen，

1、处chu于yu可ke调tiao度du状zhuang态tai（挂gua起qi），此ci状zhuang态tai下xia的de线xian程cheng正zheng在zai等deng待daiCPU分fen配pei时shi间jian片pian给gei它ta来lai执zhi行xing自zi己ji的de操cao作zuo

2、等deng待dai状zhuang态tai，此ci时shi的de线xian程cheng我wo们men可ke以yi称cheng它ta处chu在zai不bu可ke调tiao度du状zhuang态tai，CPU绝jue不bu会hui在zai等deng待dai事shi件jian未wei发fa生sheng之zhi前qian分fen配pei时shi间jian片pian给gei它ta，例li如ru一yi个ge线xian程cheng正zheng在zai等deng待dai某mou件jian事shi情qing的de发fa生sheng，就jiu比bi如ru前qian边bian说shuo的de等deng待dai事shi件jian内nei核gai对dui象xiang的de状zhuang态tai变bian为wei已yi通tong知zhi

3、CPU已yi分fen配pei时shi间jian片pian给gei线xian程cheng，它ta正zheng在zai执zhi行xing自zi己ji的de操cao作zuo。

假jia如ru我wo们men使shi用yong事shi件jian内nei核gai对dui象xiang来lai完wan成cheng一yi些xie线xian程cheng的de同tong步bu，那na么me前qian面mian曾zeng经jing说shuo过guo，当dang等deng待dai函han数shu检jian测ce到dao事shi件jian内nei核gai对dui象xiang的de状zhuang态tai为wei未wei通tong知zhi状zhuang态tai时shi，此ci线xian程cheng将jiang处chu于yu等deng待dai状zhuang态tai，此ci时shi线xian程cheng不bu会hui使shi用yongCPU，而er如ru果guo使shi用yong前qian面mian介jie绍shao的de那na种zhong反fan复fu判pan断duan变bian量liang的de方fang法fa，那na么me此ci线xian程cheng将jiang占zhan用yongCPU资zi源yuan，这zhe很hen重chong要yao，我wo始shi终zhong认ren为wei，对dui于yu一yi个ge合he格ge的de程cheng序xu员yuan而er言yan，绝jue对dui不bu要yao无wu谓wei的de浪lang费fei客ke户hu的deCPU资zi源yuan。

虽sui然ran我wo说shuo上shang面mian那na种zhong循xun环huan判pan断duan公gong共gong状zhuang态tai位wei的de办ban法fa不bu可ke取qu，但dan它ta却que反fan映yang了le线xian程cheng同tong步bu的de思si想xiang，即ji使shi我wo们men调tiao用yong那na些xie用yong于yu同tong步bu的deAPI函han数shu，事shi实shi上shang，同tong步bu的de思si想xiang也ye是shi如ru此ci，只zhi是shi实shi现xian的de方fang法fa不bu同tong而er已yi。

信xin号hao量liang

信xin号hao量liang内nei核gai对dui象xiang用yong于yu对dui资zi源yuan进jin行xing计ji数shu。它ta们men与yu所suo有you内nei核gai对dui象xiang一yi样yang，包bao含han一yi个ge使shi用yong数shu量liang，但dan是shi它ta们men也ye包bao含han另ling外wai两liang个ge带dai符fu号hao的de32位wei值zhi，一yi个ge是shi最zui大da资zi源yuan数shu量liang，一yi个ge是shi当dang前qian资zi源yuan数shu量liang。最zui大da资zi源yuan数shu量liang用yong于yu标biao识shi信xin标biao能neng够gou控kong制zhi的de资zi源yuan的de最zui大da数shu量liang，而er当dang前qian资zi源yuan数shu量liang则ze用yong于yu标biao识shi当dang前qian可ke以yi使shi用yong的de资zi源yuan的de数shu量liang。

信xin号hao量liang的de使shi用yong规gui则ze如ru下xia：

• 如ru果guo当dang前qian资zi源yuan的de数shu量liang大da于yu0，则ze发fa出chu信xin标biao信xin号hao。

• 如ru果guo当dang前qian资zi源yuan数shu量liang是shi0，则ze不bu发fa出chu信xin标biao信xin号hao。

• 系xi统tong决jue不bu允yuan许xu当dang前qian资zi源yuan的de数shu量liang为wei负fu值zhi。

• 当dang前qian资zi源yuan数shu量liang决jue不bu能neng大da于yu最zui大da资zi源yuan数shu量liang。

创chuang建jian一yi个ge信xin号hao量liang内nei核gai对dui象xiang

HANDLE CreateSemaphore(

LPSECURITY_ATTRIBUTES lpSemaphoreAttributes, // pointer to security attributes

LONG lInitialCount, // initial count

LONG lMaximumCount, // maximum count

LPCTSTR lpName // pointer to semaphore-object name

);

和he大da多duo数shu创chuang建jian内nei核gai对dui象xiang的de函han数shu一yi样yang，它ta的de第di一yi个ge参shen数shu用yong来lai接jie受shou安an全quan信xin息xi，通tong常chang我wo们men用yongNULL来lai表biao示shi默mo认ren，最zui后hou一yi个ge参shen数shu为wei创chuang建jian这zhe个ge信xin号hao量liang的de名ming字zi，此ci名ming字zi可ke以yi使shi得de我wo们men在zai其qi他ta的de进jin程cheng中zhong使shi用yong此ci信xin号hao量liang，lInitialCount参shen数shu代dai表biao创chuang建jian信xin号hao两liang时shi允yuan许xu资zi源yuan访fang问wen的de个ge数shu，lMaximumCount用yong来lai指zhi定ding最zui大da资zi源yuan数shu，不bu要yao让ranglInitialCount大da于yulMaximumCount。

使shi用yongCreate***创chuang建jian内nei核gai对dui象xiang时shi，要yao注zhu意yi一yi个ge问wen题ti，例li如ru，如ru果guo已yi经jing有you一yi个ge进jin程chengA创chuang建jian了le一yi个ge名ming为wei'wudi_1982'的de信xin号hao量liang内nei核gai对dui象xiang，当dang另ling外wai一yi个ge进jin程chengB也ye试shi图tu创chuang建jian名ming字zi为wei'wudi_1982'的de内nei核gai对dui象xiang的de时shi候hou，系xi统tong首shou先xian要yao查cha看kan是shi否fou已yi经jing存cun在zai一yi个ge名ming字zi为wei'wudi_1982'的de内nei核gai对dui象xiang。由you于yu确que实shi存cun在zai一yi个ge带dai有you该gai名ming字zi的de对dui象xiang，因yin此ci内nei核gai要yao检jian查cha对dui象xiang的de类lei型xing。如ru果guo类lei型xing相xiang同tong（例li如ru都dou是shi信xin号hao量liang内nei核gai对dui象xiang），此ci时shi系xi统tong会hui执zhi行xing一yi次ci安an全quan检jian查cha，以yi确que定ding调tiao用yong者zhe是shi否fou拥yong有you对dui该gai对dui象xiang的de完wan整zheng的de访fang问wen权quan。如ru果guo拥yong有you这zhe种zhong访fang问wen权quan，系xi统tong就jiu在zai进jin程chengB的de句ju柄bing表biao中zhong找zhao出chu一yi个ge空kong项xiang目mu，并bing对dui该gai项xiang目mu进jin行xing初chu始shi化hua，使shi该gai项xiang目mu指zhi向xiang现xian有you的de内nei核gai对dui象xiang。如ru果guo该gai对dui象xiang类lei型xing不bu匹pi配pei，或huo者zhe调tiao用yong者zhe被bei拒ju绝jue访fang问wen，那na么meCreate****将jiang运yun行xing失shi败bai（返fan回huiNULL）。

打da开kai一yi个ge现xian有you的de信xin号hao量liang

HANDLE OpenSemaphore(

DWORD dwDesiredAccess, // access flag

BOOL bInheritHandle, // inherit flag

LPCTSTR lpName // pointer to semaphore-object name

);

参shen数shudwDesiredAccess代dai表biao了le访fang问wen权quan限xian，bInheritHandle参shen数shu表biao明ming子zi进jin程cheng是shi否fou可ke继ji承cheng，最zui后hou一yi个ge参shen数shulpName 用yong于yu指zhi明ming内nei核gai对dui象xiang的de名ming字zi。不bu能neng为wei该gai参shen数shu传chuan递diNULL，必bi须xu传chuan递di以yi0结jie尾yi的de地di址zhi。这zhe些xie函han数shu要yao搜sou索suo内nei核gai对dui象xiang的de单dan个ge名ming空kong间jian，以yi便bian找zhao出chu匹pi配pei的de空kong间jian。如ru果guo不bu存cun在zai带dai有you指zhi定ding名ming字zi的de内nei核gai对dui象xiang，该gai函han数shu返fan回huiNULL，GetLastError返fan回hui2（ERROR_FILE_NOT_FOUND）。但dan是shi，如ru果guo存cun在zai带dai有you指zhi定ding名ming字zi的de内nei核gai对dui象xiang，并bing且qie它ta是shi相xiang同tong类lei型xing的de对dui象xiang，那na么me系xi统tong就jiu要yao查cha看kan是shi否fou允yuan许xu执zhi行xing所suo需xu的de访fang问wen（通tong过guodwDesiredAccess参shen数shu进jin行xing访fang问wen）。如ru果guo拥yong有you该gai访fang问wen权quan，调tiao用yong进jin程cheng的de句ju柄bing表biao就jiu被bei更geng新xin，对dui象xiang的de使shi用yong计ji数shu被bei递di增zeng。如ru果guo为weibInheritHandle,参shen数shu传chuan递diTRUE，那na么me返fan回hui的de句ju柄bing将jiang是shi可ke继ji承cheng的de。调tiao用yongCreate*函han数shu与yu调tiao用yongOpen*函han数shu之zhi间jian的de主zhu要yao差cha别bie是shi，如ru果guo对dui象xiang并bing不bu存cun在zai，那na么meCreate*函han数shu将jiang创chuang建jian该gai对dui象xiang，而erOpen*函han数shu则ze运yun行xing失shi败bai。

通tong过guo调tiao用yongReleaseSemaphore函han数shu，线xian程cheng就jiu能neng够gou对dui信xin标biao的de当dang前qian资zi源yuan数shu量liang进jin行xing递di增zeng

BOOL ReleaseSemaphore(

HANDLE hSemaphore, // handle of the semaphore object

LONG lReleaseCount, // amount to add to current count

LPLONG lpPreviousCount // address of previous count

);

参shen数shuhSemaphore代dai表biao了le要yao操cao作zuo内nei核gai对dui象xiang的de句ju柄bing，lReleaseCount表biao明ming该gai函han数shu此ci值zhi添tian加jia给gei信xin标biao的de当dang前qian资zi源yuan数shu量liang，通tong常chang我wo们men用yong1。lpPreviousCount返fan回hui当dang前qian资zi源yuan数shu量liang的de原yuan始shi值zhi，大da多duo数shu的de时shi候hou我wo们men并bing不bu关guan心xin这zhe个ge数shu值zhi，所suo以yi一yi般ban赋fu值zhi为weiNULL。

一yi个ge例li子zi：

对dui上shang述shu例li子zi操cao作zuo的de说shuo明ming：

首shou先xian程cheng序xu通tong过guo一yi个ge按an钮niu来lai生sheng成cheng一yi个ge信xin号hao量liang内nei核gai对dui象xiang，当dang前qian使shi用yong计ji数shu是shi1，最zui大da为wei3，这zhe里li，如ru果guo你ni有you兴xing趣qu，你ni可ke以yi将jiang当dang前qian使shi用yong计ji数shu改gai为wei2，从cong而er你ni可ke以yi观guan察cha到dao信xin号hao量liang内nei核gai对dui象xiang和he其qi他ta内nei核gai对dui象xiang（例li如ru互hu斥chi）的de最zui大da区qu别bie。当dang信xin号hao量liang已yi经jing生sheng成cheng之zhi后hou，点dian击ji按an钮niu创chuang建jian三san个ge线xian程cheng，线xian程cheng根gen据ju信xin号hao量liang的de名ming字zi通tong过guoOpenSemaphore来lai打da开kai，这zhe样yang做zuo的de一yi个ge好hao处chu是shi，你ni可ke以yi同tong时shi多duo次ci执zhi行xing此ci程cheng序xu，例li如ru你ni将jiang这zhe个ge程cheng序xu同tong时shi打da开kai了le3个ge，在zai其qi中zhong一yi个ge中zhong，首shou先xian设she置zhi信xin号hao量liang，然ran后hou让rang其qi他ta的de程cheng序xu都dou执zhi行xing线xian程cheng操cao作zuo，你ni会hui发fa现xian，他ta们men依yi然ran同tong步bu的de很hen好hao。这zhe是shi临lin界jie区qu无wu法fa做zuo到dao的de。

对dui代dai码ma的de一yi些xie说shuo明ming：

1、多duo个ge进jin程cheng之zhi间jian来lai完wan成cheng同tong步bu。在zai前qian面mian的de例li子zi中zhong，我wo都dou是shi使shi用yong一yi个ge全quan军jun变bian量liang***:Thandle来lai记ji录lu内nei核gai对dui象xiang，以yi使shi得de我wo们men可ke以yi在zai多duo个ge线xian程cheng中zhong访fang问wen同tong一yi个ge内nei核gai对dui象xiang，这zhe里li，我wo没mei有you再zai使shi用yong这zhe个ge办ban法fa，而er是shi利li用yong了le名ming字zi，只zhi所suo以yi要yao这zhe么me做zuo，是shi因yin为wei，如ru果guo你ni给gei内nei核gai对dui象xiang起qi一yi个ge名ming字zi，那na么me你ni可ke以yi方fang便bian的de在zai其qi他ta线xian程cheng中zhong使shi用yong同tong一yi个ge内nei核gai对dui象xiang。这zhe也ye是shi使shi用yong内nei核gai对dui象xiang完wan成cheng同tong步bu和he使shi用yong临lin界jie区qu方fang式shi最zui大da的de不bu同tong，使shi用yong临lin界jie区qu，你ni只zhi能neng在zai同tong一yi个ge进jin程cheng中zhong来lai完wan成cheng同tong步bu。你ni完wan成cheng可ke以yi将jiang上shang述shu代dai码ma整zheng理li之zhi后hou做zuo成cheng一yi个ge程cheng序xu，然ran后hou同tong时shi执zhi行xing多duo个ge此ci程cheng序xu，来lai观guan察cha效xiao果guo。即ji使shi不bu再zai同tong一yi个ge进jin程cheng之zhi中zhong，线xian程cheng依yi然ran可ke以yi很hen好hao的de完wan成cheng同tong步bu。

2、Access Mask Format.在zai利li用yong名ming字zi使shi用yong内nei核gai对dui象xiang时shi，我wo们men用yong到daoOpenSemaphore来lai完wan成cheng操cao作zuo，前qian面mian说shuo了le，它ta的de第di一yi个ge参shen数shu用yong来lai决jue定ding访fang问wen权quan限xian，事shi实shi上shang，其qi他ta的de内nei核gai对dui象xiang，例li如ru互hu斥chi，他ta们men的deopen*操cao作zuo都dou是shi如ru此ci。这zhe个ge用yong来lai决jue定ding权quan限xian的de参shen数shu至zhi关guan重chong要yao，在zai上shang面mian的de代dai码ma中zhong，我wo定ding义yi了le一yi个ge常chang量liangconst SEMAPHORE_ALL_ACCESS=$1F0003;，如ru果guo你ni在zaiDLEPHI中zhong使shi用yong过guo互hu斥chi对dui象xiang来lai完wan成cheng同tong步bu，你ni会hui觉jiao得de不bu可ke理li解jie，因yin为wei在zai使shiOpenMutex函han数shu打da开kai互hu斥chi对dui象xiang时shi，第di一yi个ge参shen数shu你ni可ke以yi直zhi接jie使shi用yongMUTEX_ALL_ACCESS，那na时shi因yin为weiDELPHI的dewindows单dan元yuan中zhong存cun在zai对dui它ta的de定ding义yi，看kanMSDN的de帮bang助zhu文wen档dang，你ni会hui发fa现xian使shi用yong信xin号hao量liang时shi候hou，也ye有you一yi个ge类lei似si的de已yi经jing定ding义yi的de常chang量liangSEMAPHORE_ALL_ACCESS ，不bu过guo很hen可ke惜xi，DELPHI中zhong并bing没mei有you定ding义yi这zhe个ge常chang量liang，所suo以yi我wo们men不bu得de不bu自zi己ji定ding义yi。另ling外wai只zhi得de注zhu意yi的de一yi点dian是shi，通tong常chang情qing况kuang下xia，我wo们men都dou是shi使shi用yong$1F0003，但dan有you时shi候hou你ni不bu得de不bu使shi用yong其qi他ta的de权quan限xian信xin息xi，此ci时shi，你ni必bi须xu注zhu意yi的de一yi点dian是shi，你ni要yao让rang权quan限xian中zhong包bao含hanSEMAPHORE_MODIFY_STATE(0x0002)这zhe个ge信xin息xi，在zaiMSDN中zhong，它ta的de说shuo明ming如ru下xia，Modify state access, which is required for the ReleaseSemaphore function.你ni可ke以yi做zuo将jiang我wo上shang面mian的de代dai码ma进jin行xing简jian单dan修xiu来lai来lai测ce试shi，例li如ru你ni将jiangSEMAPHORE_ALL_ACCESS定ding义yi为weiSTANDARD_RIGHTS_REQUIRED or SYNCHRONIZE，那na么me在zai程cheng序xu执zhi行xing的de时shi候hou，你ni会hui发fa现xian只zhi有you第di一yi个ge获huo得deCPU调tiao度du的de线xian程cheng可ke以yi正zheng常chang完wan成cheng操cao作zuo，而er其qi他ta等deng待dai此ci信xin号hao量liang的de线xian程cheng将jiang永yong远yuan的de等deng待dai下xia去qu，原yuan因yin很hen简jian单dan，就jiu是shi刚gang才cai贴tie出chu的deMSDN上shang的de那na一yi句ju话hua。根gen据ju那na一yi句ju话hua，如ru果guo你ni将jiangSEMAPHORE_ALL_ACCESS 定ding义yi为wei$1F0002，你ni会hui发fa现xian，程cheng序xu也ye没mei有you问wen题ti。为wei什shen么me，这zhe就jiu要yao说shuo到daoOpenSemaphore的dedwDesiredAccess参shen数shu，那na么me你ni就jiu要yao了le解jieAccess Mask Format，可ke以yi根gen据ju下xia面mian的de图tu来lai加jia深shen理li解jie。具ju体ti参shen考kaoMSDN的de帮bang助zhu