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FuncCandidateList
该结构体存储检索得到的所有可能选中的函数或操作符链表.

/**Thisstructureholdsalistofpossiblefunctionsoroperators*foundbynamespacelookup.Eachfunction/operatorisidentified*byOIDandbyargumenttypes;thelistmustbeprunedbytype*resolutionrulesthatareembodiedintheparser,nothere.*SeeFuncnameGetCandidates'scommentsformoreinfo.*该结构体存储检索得到的所有可能选中的函数或操作符链表.*每一个函数/操作符通过OID和参数类型唯一确定,*通过集成到分析器中的typeresolutionrules来确定裁剪该链表(但不是在这里实现)*详细可参考FuncnameGetCandidates函数.*/typedefstruct_FuncCandidateList{struct_FuncCandidateList*next;//用于namespace检索内部使用intpathpos;/*forinternaluseofnamespacelookup*///OIDOidoid;/*thefunctionoroperator'sOID*///参数个数intnargs;/*numberofargtypesreturned*///variadicarray的参数个数intnvargs;/*numberofargstobecomevariadicarray*///默认参数个数intndargs;/*numberofdefaultedargs*///参数位置索引int*argnumbers;/*args'positionalindexes,ifnamedcall*///参数类型Oidargs[FLEXIBLE_ARRAY_MEMBER];/*argtypes*/}*FuncCandidateList;二、源码解读

func_match_argtypes
给定候选函数列表(正确的函数名称/参数个数匹配)和输入数据类型OIDs数组,生成实际可匹配输入数据类型(完全匹配或可转换)的候选函数链表,然后符合条件的候选函数个数.

/*func_match_argtypes()**Givenalistofcandidatefunctions(havingtherightnameandnumber*ofarguments)andanarrayofinputdatatypeOIDs,produceashortlistof*thosecandidatesthatactuallyaccepttheinputdatatypes(eitherexactly*orbycoercion),andreturnthenumberofsuchcandidates.*给定候选函数列表(正确的函数名称/参数个数匹配)和输入数据类型OIDs数组,*生成实际可匹配输入数据类型(完全匹配或可转换)的候选函数链表,然后符合条件的候选函数个数**Notethatcan_coerce_typewillassumethatUNKNOWNinputsarecoercibleto*anything,socandidateswillnotbeeliminatedonthatbasis.*can_coerce_type函数假定UNKNOWN输入可转换为任意类型.**NB:okaytomodifyinputliststructure,aslongaswefindatleast*onematch.Ifnomatchatall,thelistmustremainunmodified.*注意:如果只是找到一个匹配的候选函数,修改输入链表结构是OK的.如无匹配,则链表保持不变.*/intfunc_match_argtypes(intnargs,Oid*input_typeids,FuncCandidateListraw_candidates,FuncCandidateList*candidates)/*returnvalue*/{FuncCandidateListcurrent_candidate;//当前候选FuncCandidateListnext_candidate;//下一候选intncandidates=0;*candidates=NULL;for(current_candidate=raw_candidates;current_candidate!=NULL;current_candidate=next_candidate)//遍历候选函数{next_candidate=current_candidate->next;if(can_coerce_type(nargs,input_typeids,current_candidate->args,COERCION_IMPLICIT))//可匹配输入数据类型(完全匹配或可转换){current_candidate->next=*candidates;*candidates=current_candidate;ncandidates++;}}returnncandidates;}/*func_match_argtypes()*/

在pg_operator中,输入参数类型与operator的参数类型匹配或可转换,可进入候选函数链表.

测试脚本

createcast(integerastext)withinoutasimplicit;selectid||'X'fromt_cast;

跟踪分析

(gdb)cContinuing.Breakpoint2,oper_select_candidate(nargs=2,input_typeids=0x7ffeb9cca190,candidates=0x13db8a0,operOid=0x7ffeb9cca22c)atparse_oper.c:330330ncandidates=func_match_argtypes(nargs,input_typeids,(gdb)p*candidates$1={next=0x13db870,pathpos=0,oid=3284,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db8c8}(gdb)p*candidates->next$2={next=0x13db840,pathpos=0,oid=3681,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db898}(gdb)p*candidates->next->next$3={next=0x13db810,pathpos=0,oid=3633,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db868}(gdb)p*candidates->next->next->next$4={next=0x13db7e0,pathpos=0,oid=2780,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db838}(gdb)p*candidates->next->next->next->next$5={next=0x13db7b0,pathpos=0,oid=374,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db808}(gdb)p*candidates->next->next->next->next->next$6={next=0x13db780,pathpos=0,oid=349,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db7d8}(gdb)p*candidates->next->next->next->next->next->next$7={next=0x13db750,pathpos=0,oid=375,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db7a8}(gdb)p*candidates->next->next->next->next->next->next->next$8={next=0x13db720,pathpos=0,oid=1797,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db778}(gdb)p*candidates->next->next->next->next->next->next->next->next$9={next=0x13db6f0,pathpos=0,oid=2779,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db748}(gdb)p*candidates->next->next->next->next->next->next->next->next->next$10={next=0x13db6c0,pathpos=0,oid=654,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db718}(gdb)p*candidates->next->next->next->next->next->next->next->next->next->next$11={next=0x0,pathpos=0,oid=2018,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db6e8}(gdb)p*candidates->next->next->next->next->next->next->next->next->next->next->nextCannotaccessmemoryataddress0x0(gdb)n334if(ncandidates==0)(gdb)339if(ncandidates==1)(gdb)349candidates=func_select_candidate(nargs,input_typeids,candidates);(gdb)pncandidates$12=2(gdb)p*candidates$13={next=0x13db810,pathpos=0,oid=374,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db808}(gdb)p*candidates->next$14={next=0x0,pathpos=0,oid=2780,nargs=2,nvargs=0,ndargs=0,argnumbers=0x0,args=0x13db838}(gdb)p*candidates->next->nextCannotaccessmemoryataddress0x0(gdb)

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