问题
多线程libcurl运行一段时间后出现崩掉，没有确定的点，没有确定的URL。一直查看源代码没有问题，最后通过debug跟踪发现是在访问SSL的时候出现的crash。
才想起来openssl是不支持多线程的，要自己做加锁处理。而且libcurl中并没有支持相关的加锁操作。
解决办法：
在初始化libcurl的时候为openssl创建一个互斥锁函数，一个回调函数传给openss
openssl锁l函数原形 ：void (* func )(int ,int , const char * ,int)
设置方式：CRYPTO_set_locking_callback(void (* func )(int ,int , const char * ,int));
设置这样一个函数还不够，另外还要配置一个锁id回调函数，这个可以参考openssl多线程下的使用相关。
id函数原形：unsigned int (*func)(void)
设置方式：CRYPTO_set_id_callback(unsigned int (*func)(void));
通过这两个设置就可以解决HTTPS多线程请求出现crash的问题。
代码示例：
下面是引用了libcurl示例的一个代码http://curl.haxx.se/libcurl/c/opensslthreadlock.html
最关键就是，两个callback的实现，还有初始化锁（init_locks）和释放锁(kill_locks)的位置
- #define USE_OPENSSL
-
- #include <stdio.h>
- #include <pthread.h>
- #include <curl/curl.h>
-
- #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 <openssl/crypto.h>
- 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<CRYPTO_num_locks(); 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<CRYPTO_num_locks(); i++)
- pthread_mutex_destroy(&(lockarray[i]));
-
- OPENSSL_free(lockarray);
- }
- #endif
-
- #ifdef USE_GNUTLS
- #include <gcrypt.h>
- #include <errno.h>
-
- 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< NUMT; i++) {
- error = pthread_create(&tid[i],
- NULL, /* default attributes please */
- 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]);
- }
-
- /* now wait for all threads to terminate */
- for(i=0; i< NUMT; i++) {
- error = pthread_join(tid[i], NULL);
- fprintf(stderr, "Thread %d terminated\n", i);
- }
-
- kill_locks();
-
- return 0;
- }