多線程中使用curl致coredump問題

2019-11-06 08:04:36

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供稿：網(wǎng)友

coredump時的調(diào)用棧：#0 0x081eff2c in addbyter ()#1 0x081f05b8 in dPRintf_formatf ()#2 0x081f15cf in curl_mvsnprintf ()#3 0x081f0079 in curl_msnprintf ()#4 0x081ef55c in Curl_failf ()#5 0x081fa1a3 in Curl_resolv_timeout ()#6 0xeb8fbdd4 in ?? ()#7 0x00000000 in ?? ()coredump的原因是因為curl的DNS解析超時控制是使用SIGALARM實現(xiàn)的。這樣導(dǎo)致發(fā)現(xiàn)SIGALARM會出現(xiàn)多線程修改同一個全局變量，由此產(chǎn)生了COREDUMP。問題發(fā)生的前提是設(shè)置了CURLOPT_TIMEOUT或CURLOPT_CONNECTTIMEOUT，并且值不為0。解決辦法：1) 設(shè)置CURLOPT_NOSIGNAL的值為12) 使用c-ares（configure時指定參數(shù)--enable-ares）lib/curl_setup.h（異步模式使用c-ares控制DNS解析超時）：只有當(dāng)configure時指定了--enable-ares才會定義USE_ARES。#ifdef USE_ARES# define CURLRES_ASYNCH# define CURLRES_ARES/* now undef the stock libc functions just to avoid them being used */# undef HAVE_GETADDRINFO# undef HAVE_GETHOSTBYNAME#elif defined(USE_THREADS_POSIX) || defined(USE_THREADS_WIN32)# define CURLRES_ASYNCH# define CURLRES_THREADED#else# define CURLRES_SYNCH#endiflib/hostip.c（同步模式使用ALARM控制DNS解析超時）：只有定義了CURLRES_SYNCH，才可能定義USE_ALARM_TIMEOUT。#if defined(CURLRES_SYNCH) && / defined(HAVE_ALARM) && defined(SIGALRM) && defined(HAVE_SIGSETJMP)/* alarm-based timeouts can only be used with all the dependencies satisfied */#define USE_ALARM_TIMEOUT#endif相關(guān)源代碼：lib/asyn-ares.c:Curl_resolver_getaddrinfolib/hostasyn.c（基于c-ares的異步版本Curl_getaddrinfo）：Curl_resolver_getaddrinfo <-- Curl_getaddrinfo從緩存中找（hostip.c）:fetch_addr <-- Curl_resolvhostip.c:Curl_ipv4_resolve_r <-- Curl_getaddrinfo <-- Curl_resolvhostip.c:curl_jmpenv <-- sigaction(SIGALRM, alarmfunc)/sigsetjmp(curl_jmpenv) <- Curl_resolv_timeout <- url.c:Curl_resolv_timeout(hostname) <-- resolve_server <-- create_conn <-- Curl_connect multi.c:Curl_connect <--transfer.cCurl_connect <-- Curl_reconnect_requesturl.c:Curl_reconnect_request <-- Curl_domulti.c:Curl_do <-- multi_runsingle <-- curl_multi_perform <-- multi_socket <-- curl_multi_socket

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