作者：原文W | 来源：互联网 | 2023-05-17 13:32
用libcurl一段时间遇到莫名其妙的程序崩溃的情况，开始觉得是线程栈溢出导致的段错误，专门增加了线程栈的大小，还是有问题。线程也是分离的。用valgrind定位到问题可能出现在cur
用libcurl一段时间遇到莫名其妙的程序崩溃的情况，开始觉得是线程栈溢出导致的段错误，专门增加了线程栈的大小，还是有问题。线程也是分离的。用valgrind定位到问题可能出现在curl的调用上。
排查的时候也发现了libcurl一些额外的坑，现做个总结笔记。
1.、
线程使用libcurl访问时，设置了超时时间，而libcurl库不会为这个超时信号做任何处理，信号产生而没有信号句柄处理，可能导致程序退出。用以下选项禁止访问超时的时候抛出超时信号。
curl_setopt(curl, CURLOPT_NOSIGNAL,1L);
2、
正常使用流程是先调用curl_global_init初始化资源，而这个函数不是线程安全的。curl_easy_init发现没有做初始化时会自动初始化，多个线程同时进行curl_easy_init时会导致异常。curl官方建议在主线程中先做初始化。
curl_global_init(CURL_GLOBAL_ALL);
3、
用valgrind调试，做压力测试多线程运行时，valgrind弹出类似访问冲突的错误，把错误定位到libcurl的互斥访问的处理上。
大致是进行访问设计到ssl的东西的时候，需要做相应的加锁处理，libcurl源码没有加这块处理，不过给了个针对这种情况加锁的例子，总的来说curl的示例代码很重要很有用。
https://curl.haxx.se/libcurl/c/example.html
[cpp] view plain copy print?
- #define USE_OPENSSL
-
- #include
- #include
- #include
-
- #define NUMT 4
-
-
- static pthread_mutex_t *lockarray;
-
- #ifdef USE_OPENSSL
- #include
- static void lock_callback(int mode, int type, char *file, int line)
- {
- (void)file;
- (void)line;
- if(mode & CRYPTO_LOCK) {
- pthread_mutex_lock(&(lockarray[type]));
- }
- else {
- pthread_mutex_unlock(&(lockarray[type]));
- }
- }
-
- static unsigned long thread_id(void)
- {
- unsigned long ret;
-
- ret=(unsigned long)pthread_self();
- return ret;
- }
-
- static void init_locks(void)
- {
- int i;
-
- lockarray=(pthread_mutex_t *)OPENSSL_malloc(CRYPTO_num_locks() *
- sizeof(pthread_mutex_t));
- for(i=0; i
- pthread_mutex_init(&(lockarray[i]), NULL);
- }
-
- CRYPTO_set_id_callback((unsigned long (*)())thread_id);
- CRYPTO_set_locking_callback((void (*)())lock_callback);
- }
-
- static void kill_locks(void)
- {
- int i;
-
- CRYPTO_set_locking_callback(NULL);
- for(i=0; i
- pthread_mutex_destroy(&(lockarray[i]));
-
- OPENSSL_free(lockarray);
- }
- #endif
-
- #ifdef USE_GNUTLS
- #include
- #include
-
- GCRY_THREAD_OPTION_PTHREAD_IMPL;
-
- void init_locks(void)
- {
- gcry_control(GCRYCTL_SET_THREAD_CBS);
- }
-
- #define kill_locks()
- #endif
-
-
- const char * const urls[]= {
- ”https://www.example.com/”,
- ”https://www2.example.com/”,
- ”https://www3.example.com/”,
- ”https://www4.example.com/”,
- };
-
- static void *pull_one_url(void *url)
- {
- CURL *curl;
-
- curl = curl_easy_init();
- curl_easy_setopt(curl, CURLOPT_URL, url);
-
-
- curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
- curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
- curl_easy_perform(curl);
- curl_easy_cleanup(curl);
-
- return NULL;
- }
-
- int main(int argc, char **argv)
- {
- pthread_t tid[NUMT];
- int i;
- int error;
- (void)argc;
- (void)argv;
-
-
- curl_global_init(CURL_GLOBAL_ALL);
-
- init_locks();
-
- for(i=0; i< NUMT; i++) {
- error = pthread_create(&tid[i],
- NULL,
- pull_one_url,
- (void *)urls[i]);
- if(0 != error)
- fprintf(stderr, ”Couldn’t run thread number %d, errno %d\n”, i, error);
- else
- fprintf(stderr, ”Thread %d, gets %s\n”, i, urls[i]);
- }
-
-
- for(i=0; i< NUMT; i++) {
- error = pthread_join(tid[i], NULL);
- fprintf(stderr, ”Thread %d terminated\n”, i);
- }
-
- kill_locks();
-
- return 0;
- }
#define USE_OPENSSL
#include #include #include #define NUMT 4/* we have this global to let the callback get easy access to it */ static pthread_mutex_t *lockarray;#ifdef USE_OPENSSL#include static void lock_callback(int mode, int type, char *file, int line){ (void)file; (void)line; if(mode & CRYPTO_LOCK) { pthread_mutex_lock(&(lockarray[type])); } else { pthread_mutex_unlock(&(lockarray[type])); }}static unsigned long thread_id(void){ unsigned long ret; ret=(unsigned long)pthread_self(); return ret;}static void init_locks(void){ int i; lockarray=(pthread_mutex_t *)OPENSSL_malloc(CRYPTO_num_locks() * sizeof(pthread_mutex_t)); for(i=0; i#include GCRY_THREAD_OPTION_PTHREAD_IMPL;void init_locks(void){ gcry_control(GCRYCTL_SET_THREAD_CBS);}#define kill_locks()#endif/* List of URLs to fetch.*/ const char * const urls[]= { "https://www.example.com/", "https://www2.example.com/", "https://www3.example.com/", "https://www4.example.com/",};static void *pull_one_url(void *url){ CURL *curl; curl = curl_easy_init(); curl_easy_setopt(curl, CURLOPT_URL, url); /* this example doesn't verify the server's certificate, which means we might be downloading stuff from an impostor */ curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L); curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L); curl_easy_perform(curl); /* ignores error */ curl_easy_cleanup(curl); return NULL;}int main(int argc, char **argv){ pthread_t tid[NUMT]; int i; int error; (void)argc; /* we don't use any arguments in this example */ (void)argv; /* Must initialize libcurl before any threads are started */ curl_global_init(CURL_GLOBAL_ALL); init_locks(); for(i=0; i
未完待续。。。
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