libcurl-“ curl_easy_cleanup（）”导致malloc错误（C ++）

Question

When running my code (pertinent sections pasted below), I periodically get the following error:

program(34010,0x70000e58b000) malloc: *** error for object 0x7fc43d93fcf0: pointer being freed was not allocated set a breakpoint in malloc_error_break to debug Signal: SIGABRT (signal SIGABRT)

I am running multi-threaded C++ code on a Macbook (OS-10.13) wherein different threads make use of the code in question simultaneously. To my knowledge, libcurl is indeed thread safe as long as I do not utilize the same "curl handle" (which I understand to be an instance of "CURL" aka "CURL *curl = curl_easy_init();") in two different threads at the same time. In my case, since each thread calls the function separately and initializes a new instance of a CURL object, I should be "safe", right? Hopefully there is something obvious that I'm missing that is causing me (or lib curl in this case) to attempt to free memory that has already been freed. If there is any more information I should have included (below) please don't hesitate to let me know.

The function that seg faults is

string http_lib::make_get_request(string url)

on the line that reads

curl_easy_cleanup(curl);

and sometimes (less often) on the line that reads

res = curl_easy_perform(curl);

Below is what I think would be the pertinent sections of my code:

size_t http_lib::CurlWrite_CallbackFunc_StdString(void *contents, size_t size, size_t nmemb, std::string *s)
{
    size_t newLength = size*nmemb;
    size_t oldLength = s->size();
    try
    {
        s->resize(oldLength + newLength);
    }
    catch(std::bad_alloc &e)
    {
        //handle memory problem
        return 0;
    }

    std::copy((char*)contents,(char*)contents+newLength,s->begin()+oldLength);
    return size*nmemb;
}

string http_lib::make_post_request(string url, vector<string> headers, string post_params) {
    CURL *curl;
    CURLcode res;

    curl = curl_easy_init();
    string s;
    if(curl)
    {
        struct curl_slist *chunk = NULL;

        for(int i=0; i<headers.size(); i++){
            /* Add a custom header */
            chunk = curl_slist_append(chunk, headers[i].c_str());
        }

        /* set our custom set of headers */
        res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, chunk);
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, post_params.c_str());
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L); //only for https
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L); //only for https
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, CurlWrite_CallbackFunc_StdString);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &s);
        if(networking_debug){
            curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L); //verbose output
        }

        /* Perform the request, res will get the return code */
        res = curl_easy_perform(curl);

        /* Check for errors */
        if(res != CURLE_OK)
        {
            fprintf(stderr, "curl_easy_perform() failed: %s\n",
                    curl_easy_strerror(res));
        }

        /* always cleanup */
        curl_easy_cleanup(curl);
    }

    // Debug output
    if (networking_debug){
        cout<<"Response: " << s <<endl;
    }

    return s;
}

string http_lib::make_get_request(string url) {
    //SslCurlWrapper sslObject;
    CURL *curl;
    CURLcode res;

    curl = curl_easy_init();
    string s;
    if (curl) {
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        //tell libcurl to follow redirection
        curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L); //only for https
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L); //only for https
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, CurlWrite_CallbackFunc_StdString);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &s);
        if(networking_debug){
            curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L); //verbose output
        }

        /* Perform the request, res will get the return code */
        res = curl_easy_perform(curl);
        /* Check for errors */
        if (res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));

        /* always cleanup */
        curl_easy_cleanup(curl);
    }

    if (networking_debug){
        cout << "Response: " << s << endl;
    }

    return s;
}

In main() I have

int main(int argc, char *argv[]){
    // Initialize http_lib (curl)
    curl_global_init(CURL_GLOBAL_DEFAULT);

    ... spin up 10 or so threads that make get/post requests to https site (some requests utilize the make_post_request() function and others utilize make_get_requet() function). 
}

Answer 1

CMAKE doesn't/didn't seem to want to use anything other than CURL_ROOT_DIR of "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/usr/include" for libcurl (aka curl).

Thus it was using the curl lib that mac (and/or Xcode) ships with. I haven't figured out what version that is, but I can say that not using it and instead using CURL version 7.57 is what fixed my issue.

I used "brew" package manager to

brew install curl

Doing so created /usr/local/Cellar/curl/7.57.0 directory and put all libs/includes in there.

Then I added

 -I/usr/local/Cellar/curl/7.57.0/include -L/usr/local/Cellar/curl/7.57.0/lib

to my CMAKE CMAKE_CXX_FLAGS.

TLDR; Solution was to ensure I was using the newest version of the curl lib. Now that I am, no problem.