performing curl_multi_perform from different threads causing crash - c++

Question

In the project I am working on , I am required to make a GET call and POST call when ever necessary. The "GET" call is used to create a downchannel from the server to the device to monitor for any interesting events that are happen in the cloud server. The "POST" call is used to send the data to the server. The server has a restriction that only a single connection has to be maintained with the server. Since the server supports HTTP2 , I am using "CURLMOPT_MAX_HOST_CONNECTIONS" and by setting it to 1 , I am making CURL to use 1 connection and I am using CURLMOPT_PIPELINING and by setting it to CURLPIPE_MULTIPLEX , I am multiplexing the transfers. The issue is that the code crashes when "curl_multi_perform" is called on the second thread.
PS: This is a part of my original code and might not compile/run straight away.
#include <stdio.h>
#include <string>
#include <sstream>
#include <curl.h>
#include <pthread.h>
#define EVENTS_URL "https://avs-alexa-na.amazon.com/v20160207/events"
#define DOWNCHANNEL_URL "https://avs-alexa-na.amazon.com/v20160207/directives"
CURLM *multi_handle;
CURL *downchannel_handle;
CURL *eventHttp_handle;
size_t processDownchannelResponse(void *ptr, size_t size, size_t nmemb, void *instance)
{
printf(" There is downchannel response.");
}
size_t eventResponse(void *ptr, size_t size, size_t nmemb, void *instance)
{
printf("We got eventResponse");
}
/* The downchannel thread needs to be running always
, if the transfer is done the connection is closed
we need to open a new connection and wait for more events*/
void createDownchannel()
{
int retryCount =0;
std::string downchURL = DOWNCHANNEL_URL;
long response_code;
int runninghandles =0;
downchannel_handle = curl_easy_init();
if(downchannel_handle == NULL){
printf("createDownchannel : Not able to create curl handle");
return ;
}
struct curl_slist *header = NULL;
header = curl_slist_append(header, "Host: avs-alexa-na.amazon.com");
header = curl_slist_append(header, "TOKEN GOES HERE");
curl_easy_setopt(downchannel_handle, CURLOPT_URL, downchURL.c_str());
curl_easy_setopt(downchannel_handle, CURLOPT_SSL_VERIFYPEER, 0L);
curl_easy_setopt(downchannel_handle, CURLOPT_SSL_VERIFYHOST, 0L);
curl_easy_setopt(downchannel_handle, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE);
curl_easy_setopt(downchannel_handle, CURLOPT_WRITEFUNCTION, processDownchannelResponse);
curl_easy_setopt(downchannel_handle, CURLOPT_WRITEDATA, NULL);
curl_easy_setopt(downchannel_handle, CURLOPT_PIPEWAIT, 1L);
if (header)
curl_easy_setopt(downchannel_handle, CURLOPT_HTTPHEADER, header);
if(multi_handle)
/* add the individual easy handle */
curl_multi_add_handle(multi_handle, downchannel_handle);
mbexitdownchannelthread = 1;
do{
CURLMcode mc;
int numfds;
mc = curl_multi_perform(multi_handle, &runninghandles);
if(mc != CURLM_OK) {
fprintf(stderr, "curl_multi failed, code %d.n", mc);
printf(“a<---curl_multi failed, code %d.n", mc);
break;
}
printf("a<--downchannel while");
// downchannel timeout can be higher 10 seconds
mc = curl_multi_wait(multi_handle, NULL, 0, 10000, &numfds);
if(mc != CURLM_OK) {
fprintf(stderr, "curl_multi failed, code %d.n", mc);
printf("a<---curl_multi failed, code %d.n", mc);
break;
}
}while(!mbexitdownchannelthread);
curl_multi_remove_handle(multi_handle, downchannel_handle);
curl_easy_cleanup(downchannel_handle);
if (header)
curl_slist_free_all(header);
}
bool getTransferStatus(CURLM *multiHandleInstance,CURL *currentHandle,std::string& contentType,int* http_status_code)
{
//check the status of transfer CURLcode return_code=0;
int msgs_left=0;
CURLMsg *msg=NULL;
CURL *eh=NULL;
CURLcode return_code;
bool msgTrasferDone = false;
while ((msg = curl_multi_info_read(multiHandleInstance, &msgs_left)))
{
if (msg->msg == CURLMSG_DONE) {
eh = msg->easy_handle;
if(currentHandle == eh)
{
msgTrasferDone = true;
return_code = msg->data.result;
if(return_code!=CURLE_OK)
{
//fprintf(stderr, "CURL error code: %d\n", msg->data.result);
printf("a<--return_code!=CURLE_OK CURL error code: %d\n", msg->data.result);
continue;
}
// Get HTTP status code
*http_status_code=0;
char* ch= NULL;
curl_easy_getinfo(eh, CURLINFO_RESPONSE_CODE, http_status_code);
printf("a<--CURLINFO_RESPONSE_CODE=%d",*http_status_code);
curl_easy_getinfo(eh, CURLINFO_CONTENT_TYPE, &ch);
contentType.clear();
if(ch!=NULL)
contentType.append(ch);
}
}
}
return msgTrasferDone;
}
int eventThread()
{
int still_running = 0;
std::string contentType;
int responseCode = 0;
int numfds = 0;
std::string postUrl;
postUrl.assign(EVENTS_URL);
// init the curl session
CURL *eventHttp_handle;
CURLcode res;
eventHttp_handle = curl_easy_init();
//assign speech buffer pointer for read callbacks
curl_easy_setopt(eventHttp_handle, CURLOPT_URL, postUrl.c_str());
curl_easy_setopt(eventHttp_handle, CURLOPT_SSL_VERIFYPEER, 0L);
curl_easy_setopt(eventHttp_handle, CURLOPT_SSL_VERIFYHOST, 0L);
curl_easy_setopt(eventHttp_handle, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE);
/* wait for pipe connection to confirm */
curl_easy_setopt(eventHttp_handle, CURLOPT_PIPEWAIT, 1L);
curl_easy_setopt(eventHttp_handle, CURLOPT_WRITEFUNCTION, eventResponse);
curl_easy_setopt(eventHttp_handle, CURLOPT_WRITEDATA, NULL);
struct curl_slist *header = NULL;
header = curl_slist_append(header, "Host: avs-alexa-na.amazon.com");
header = curl_slist_append(header, "TOKEN GOES HERE");
if (header)
curl_easy_setopt(eventHttp_handle, CURLOPT_HTTPHEADER, header);
if (multi_handle)
curl_multi_add_handle(multi_handle, eventHttp_handle);
do
{
{
CURLMcode mc;
int numfds;
mc = curl_multi_perform(multi_handle, &still_running);
if(mc != CURLM_OK) {
fprintf(stderr, "curl_multi failed, code %d.n", mc);
printf("a<---curl_multi failed, code %d.n", mc);
break;
}
mc = curl_multi_wait(multi_handle, NULL, 0, 1000, &numfds);
if(mc != CURLM_OK) {
fprintf(stderr, "curl_multi failed, code %d.n", mc);
printf("a<---curl_multi failed, code %d.n", mc);
break;
}
}
}while(!getTransferStatus(multi_handle,eventHttp_handle,contentType,&responseCode));
if (header)
curl_slist_free_all(header);
if (formpost)
{
curl_formfree(formpost);
formpost = NULL;
}
printf("a<-- CURL HTTP RESP CODE =%d",responseCode);
curl_multi_remove_handle(multi_handle, eventHttp_handle);
curl_easy_cleanup(eventHttp_handle);
return 0;
}
int main ()
{
multi_handle = curl_multi_init();
curl_multi_setopt(multi_handle, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
curl_multi_setopt(multi_handle, CURLMOPT_MAX_HOST_CONNECTIONS, 1L);
// create a downchannel thread
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
int err = pthread_create(&mPostThread, &attr, downchannelThread,NULL);
pthread_attr_destroy(&attr);
// i am doing some work here //
sleep(3);
// create a event thread
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
int err = pthread_create(&mPostThread, &attr, eventThread,NULL);
pthread_attr_destroy(&attr);
}