Can't debug: assert error with gdb (no problem without)
I'm sorry if the title is really criptic, but I don't know how to phrase my problem.
I know I can't really ask for a solution, and I normally wouldn't but this is really escaping my abilities.
Antefacts.
I developed a program using the zeromq messaging library.
I got to a point where the program works and then started going multithreading: moving a message poller outside of the main thread.
This is supported by the library.
So I devised my thread, passed it a pointer to some parameters (including the pointer to the zmq context) and went ahead.
The Problem
The code in the child thread is the same code I had in the parent, save for the facts that functions parameters are stored in a structure that gets passed to the child.
I followed every function in the child and the parameters are correct.
The code does even work (as it should) when run normally, but hangs with an assert when run in debug.
I tried following every function I could, built the library with debug symbols, using gdb from the console...
I got nothing useful.
I still don't understand why it fails with the debugger attached, and why it runs without.
, I can post the code no problem, this is the smallest minimal example iI couldd devise.
Code:
(android won't let me paste the code... I'll have to get to my computer.
Although even when I'll be able to show you the code, you'll still need the library cited above http://github.com/erupter/saettang
What value do pgm_error->domain and pgm_error->code have?
No matter how I compiled the relative library, the values are optimized out.
I tried explicitly configuring with -O0 but to no avail.
Here is my minimal test code.
It requires the Zmqcpp library found in my github project, as well as ZeroMQ library 3.2.2 compiled with pgm support.
Code:
/*
* File: main.cpp
* Author: erupter
*
* Created on January 9, 2013, 2:03 PM
*/
/*
* File: main.cpp
* Author: erupter
*
* Created on January 9, 2013, 2:03 PM
*/
#include <cstdlib>
#include <net/if.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <list>
#include <zmqcpp.h>
#define THREAD_CONTROL_IPC "ipc://saetta_th_control"
#define MULTICAST_ADDRESS "239.192.1.1"
#define MULTICAST_PORT 5678
#define ROUTER_PORT 5679
#define HEADER_CTRL "CTRL"
#define HEADER_SERVER_INFO "SERVER_INFO"
using namespace std;
std::string _local_ip_address;
std::stringstream ss;
// custom struct to hold parameters to pass to child threads
struct parameters{
// pointer to context
Zmqcpp::Context * zmqcont;
// function pointer for callbacks
void (*callback) (std::string);
//ip string to connect to
std::string ip;
//if child should bind or connect
int conntype;
//topics to subscribe
std::list<std::string> topics;
};
//child thread
void *th_subscriber (void * params);
//callback
void server_location_callback(std::string ip);
//service function to get the specified interface's address
static inline bool get_iface_address(std::string interf);
/*
*
*/
int main(int argc, char** argv) {
struct parameters myparams;
printf( "Requested interface wlan0, attempting to fetch address...\n");
if (!get_iface_address("wlan0"))
return (EXIT_FAILURE);
//create the pgm address chaining various parameters defined above plus the local ip address of the interface
ss << "epgm://" << _local_ip_address << ";" << MULTICAST_ADDRESS << ":" << MULTICAST_PORT << std::endl;
//create context
Zmqcpp::Context* mycontext = new Zmqcpp::Context(1);
//fill the parameters structure
myparams.ip = ss.str();
ss.str("");
ss.str(HEADER_SERVER_INFO);
myparams.topics.insert(myparams.topics.end(),ss.str());
myparams.conntype = ZMQCPP_CONNECT;
myparams.zmqcont=mycontext;
myparams.callback=&server_location_callback;
//create the connection string for the control socket
ss.str("");
ss << THREAD_CONTROL_IPC;
//create the control socket
Zmqcpp::Publisher *ctrlpublisher = new Zmqcpp::Publisher(mycontext, THREAD_CONTROL_IPC, ZMQCPP_BIND);
//create the child thread
pthread_t th_hndl_subber;
pthread_create(&th_hndl_subber, NULL, th_subscriber, (void *)&myparams);
while(1)
{
//send control messages over the control socket
ctrlpublisher->PubMsg(2,HEADER_CTRL,"Test");
sleep(1);
}
//garbage collection
void *status;
pthread_join(th_hndl_subber, &status);
printf("Main thread cleaning.\n");
ctrlpublisher->~Publisher();
mycontext->~Context();
printf("Main thread cleaned succesfully.");
return (EXIT_SUCCESS);
}
static inline bool get_iface_address(std::string interf)
{
int s;
struct ifreq ifr = {};
s = socket(PF_INET, SOCK_DGRAM, 0);
strncpy(ifr.ifr_name, interf.c_str(), sizeof(ifr.ifr_name));
if (ioctl(s, SIOCGIFADDR, &ifr) >= 0)
{
_local_ip_address = inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr);
printf("Detected interface IP address is %s.\nCreating sockets on this address.\n", _local_ip_address.c_str());
return true;
}
printf("Unable to get interface IP address: is the interface configured?\n");
return false;
}
void *th_subscriber (void * params)
{
//declare some service variables
int th_continue=1;
std::string server_ip;
std::stringstream ss;
std::string msgtype;
std::string msgmaster = HEADER_SERVER_INFO;
std::string temp;
//recast the pointer to the parameter structure
struct parameters *myparams = (struct parameters *) params;
//create the subscriber for the real messages we would like to get
// THIS IS WHAT TRIGGERS THE ASSERT DURING DEBUG
Zmqcpp::Subscriber *msgsubber = new Zmqcpp::Subscriber(myparams->zmqcont,&(myparams->ip), myparams->conntype);
//have it subscribe to each topic we are told to
for (std::list<std::string>::iterator it = myparams->topics.begin(); it != myparams->topics.end(); it++)
{
cout << "Subscribing to <" << *it <<">"<<std::endl;
printf("Subscribing to: <%s>\n",it->c_str());
msgsubber->SubscribeTopic(*it);
}
ss.str("");
ss << THREAD_CONTROL_IPC;
//create the control subscriber over the specified ipc control address and subscribe it
Zmqcpp::Subscriber *ctrlsubber = new Zmqcpp::Subscriber(myparams->zmqcont,THREAD_CONTROL_IPC, ZMQCPP_CONNECT);
ctrlsubber->SubscribeTopic(HEADER_CTRL);
sleep(1);
while(th_continue==1)
{
//do something silly with the control messages
ss.str("");
ss << ctrlsubber->RecvMsg();
msgtype.clear();
msgtype = ss.str();
if (!msgtype.compare(HEADER_CTRL))
{
ss.str("");
ss << "Control message: " << ctrlsubber->RecvMsg();
temp.clear();
temp.assign(ss.str());
myparams->callback(temp.c_str());
if (temp.compare("Control message: KILL")==0)
th_continue=0;
}
}
//child thread garbage collection
printf("Child thread cleaning resources.\n");
ctrlsubber->~Subscriber();
//msgsubber->~Subscriber();
printf("Child thread terminating.\n");
return(EXIT_SUCCESS);
}
void server_location_callback(std::string ip)
{
cout << ip.c_str() << std::endl;
}
If you literally cut&paste the msgsubscriber inside the main thread, obviously modifying the passed parameters, you can both run and debug the code.
As it is you can't.
warning: Source file is more recent than executable.
Not really, I had modified the phrasing of the if to see if gdb behaved any differently. It didn't.
Quote:
Originally Posted by jim mcnamara
Just because gdb shows line #1 of a multiline construct does not mean that line #1 of your if block is the problem.
If you actually want to debug it, break the if's into singletons(this is logical decompostion to monads, so by a theorem by Courcelle):
That's not exactly the problem: the if gives way to a goto statement.
But if any of the conditions triggered the conditional to go fordward, gdb ought to show the call to the goto instruction... at least for what I know.
It instead shows the program as jumping directly to the first line after the goto label.
If then it isn't so, I'll separate the various ifs.
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