Got this segfault, and I can't seem to get around it. Narrowed it down to the pthread_join() function. I'm loading libpthread dynamically.
int main(int argc, char **argv)
{
void *lib_handle;
create pthread_c;
join pthread_j;
pthread_t thrd_id;
int rc;
char *error;
lib_handle = dlopen("/lib/x86_64-linux-gnu/libpthread.so.0", RTLD_NOW);
if (!lib_handle)
{
fprintf(stderr, "%s\n", dlerror());
exit(1);
}
pthread_c = dlsym(lib_handle, "pthread_create");
pthread_j = dlsym(lib_handle, "pthread_join");
if ((error = dlerror()) != NULL)
{
fprintf(stderr, "%s\n", error);
exit(1);
}
rc = pthread_c(&thrd_id, NULL, sub, (void *)NULL);
pthread_j(thrd_id, NULL); // CAUSES SEGFAULT
printf ("testing");
dlclose(lib_handle);
return 0;
}
void* sub (void* a)
{
printf("Hello Thread, I'm the World!\n");
}
The printf() statement shows that pthread_create() is working as it should. But I need to call pthread_join() otherwise the program terminates before the thread is spun up.
Turns out you must declare the join and create typedefs to use pthread_t instead of int from sys/types.h
typedef int (*create)(pthread_t, void*, void*, void*);
typedef void (*join) (pthread_t, void*);
I think i was using an int for create which worked, but doesn't work for join()
Related
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#define MALLOC(p,s) {\
if (!((p) = malloc(s))) { \
fprintf(stderr, "insufficient memory");\
exit(EXIT_FAILURE);\
}\
}
#define IS_EMPTY(first) (!first)
typedef struct listNode* listPointer;
typedef struct listNode {
int data;
listPointer link;
}listNode;
void printList(listPointer first);
int main(void)
{
int x;
int tmpData;
listPointer first = NULL;
listPointer tmpLink = NULL;
FILE* fp = NULL;
if (!(fp = fopen("in.txt", "r"))) {
fprintf(stderr, "cannot open the file");
exit(EXIT_FAILURE);
}
while (!feof(fp)) {
fscanf(fp, "%d", &tmpData);
MALLOC(tmpLink, sizeof(listNode));
if (IS_EMPTY(first)) {
MALLOC(first, sizeof(listNode));
*tmpLink = *first;
}
tmpLink->data = tmpData;
tmpLink = tmpLink->link;
}
printList(first);
}
void printList(listPointer first)
{
for (; first; first = first->link) {
printf("%d ", first->data);
}
printf("\n");
}
We know that we can implement the insert function.
But I'm really curious about why this doesn't work.
What "first" refers to and what "tmpLink" refers to is the same
After implementing the link list while updating tmpLink,
I'm going to use "first" to print later.
I've spent almost a day just thinking about this, and I've tried debugging it, but I don't know why.
I am attempting to get the function pointer by using dlopen and dlsym, however I have been unable to get it working correctly. It fails when trying to doing the dlsym call. Following is my code.
Any help please?
#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>
int test() {
printf("%s", "test()");
return 123;
}
int main() {
char * functionname = "test";
void* handle = dlopen(NULL,RTLD_LAZY|RTLD_GLOBAL);
if (!handle) {
fprintf(stderr, "Couldn't open handle: %s\n",
dlerror());
exit(1);
}
int (*fun)() = (int (*)())dlsym(handle, functionname);
if (fun == NULL) {
fprintf(stderr, "Couldn't find function: %s\n",functionname);
exit(1);
}
int a = fun();
printf("result: %d \n", a);
}
Probably you need to specify to the linker to export the symbols as dynamic. With gcc you have to use -rdynamic.
You can check the exported dynamic symbols with objdump -T.
I would like to program a Qt programe with libcurl.
Header like this:
class WorkThread : public QThread
{
Q_OBJECT
public:
//...
void work(QString url_);
static size_t callback_get_head(void *ptr, size_t size, size_t nmemb, void *userp);
protected:
void run();
private:
QString url;
};
Source code:
//....
void WorkThread::work(QString url_)
{
url=url_;
start();
}
void WorkThread::run()
{
CURL *curl;
CURLcode res;
char buffer[512];
curl = curl_easy_init();
if(curl) {
char *liburl=url.toLatin1().data();
curl_easy_setopt(curl, CURLOPT_URL, liburl);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WorkThread::callback_get_head);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, buffer);
res = curl_easy_perform(curl);
if(res != CURLE_OK)
printf("curl_easy_perform() failed: %s\n",curl_easy_strerror(res));
curl_easy_cleanup(curl);
printf("%s \n",buffer);
}
}
size_t WorkThread::callback_get_head(void *ptr, size_t size, size_t nmemb, void *userp)
{
strcat( (char*)(userp), (char*)(ptr));
return size * nmemb;
}
In main :
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
WorkThread thread1;
WorkThread thread2;
WorkThread thread3;
thread1.work("http://hq.sinajs.cn/list=sh601006");
thread2.work("http://hq.sinajs.cn/list=sh601006");
thread3.work("http://hq.sinajs.cn/list=sh601006");
return a.exec();
}
When I compile and run , I find it that the results is different each time. What is wrong?It said "name resolve failed".But it seems that name resolve successed in thread1 and thread2.
The problem is that you're not using QThread properly. Unless you're going to change how Qt handles threads, you shouldn't be inheriting from it; You're doing it Wrong!
Your main object has the thread affinity of the main thread, though your Curl object's thread affinity is the new thread.
Separate the Curl code into a separate class, inherited from QObject and then move that to the new thread. This should solve the problems you're seeing.
This article explains how to use QThread properly.
I have a client server program where client writes a command on PIPE for server. While reading the command from Server it reads only first char of command and throws error. Can anyone help me with this?
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <sys/wait.h>
#include <mqueue.h>
#include <sys/stat.h>
#include "Functions.h"
#define MSGBUFFER_SIZE 50000
pid_t serverPid;
pid_t clientPid;
typedef struct msgbuf {
int messageLength;
int messageType;
char messageText[MSGBUFFER_SIZE];
} Message_buf;
int writePIPE(int fd, Message_buf *inputMessage){
printf("\n In write pipe message length :%d",inputMessage->messageLength);
printf("\n In write pipe message Data :%s",inputMessage->messageText);
ssize_t n=write(fd,inputMessage,inputMessage->messageLength);
printf("\n Size :%d", n);
return n;
}
ssize_t readPIPE(int fd, Message_buf *outputMessage)
{
ssize_t len;
ssize_t n;
if((n=read(fd,outputMessage,sizeof(outputMessage)))==0)
{
printf("\n Error");
return 0;
}
if((len=outputMessage->messageLength)>0)
{
printf("\n Length ---->:%d",len);
if((n=read(fd,outputMessage->messageText,strlen(outputMessage->messageText)))!=len)
printf("\n ERRRRROR expected %d got %d",len,n);
}
//printf("\n In Read PIPE: %s",outputMessage->messageText);
return len;
}
void Server(int readfd,int writefd)
{
Message_buf server_MessageBuf;
ssize_t length;
if((length=readPIPE(readfd,&server_MessageBuf))==0)
{
printf("\n End of file while reading pathname");
}
//server_MessageBuf.messageText[length]='\0';
printf("\n LENGTH :%d",server_MessageBuf.messageLength);
printf("\n Printing in server: %s\n",server_MessageBuf.messageText);
}
void Client(int readfd,int writefd)
{
char inputFileName[MAX_SIZE];
char inputOperation[MAX_SIZE];
char *cCommandInput = NULL;
char *fileOperation = NULL;
char *operation = (char *) malloc(MAX_SIZE);
int commandValidateStatus = 0;
int commandInterpretationStatus=0;
Message_buf client_MessageBuf;
for(;;)
{
while(1)
{
cCommandInput = acceptInput();
fileOperation = (char *) malloc(sizeof(cCommandInput));
strcpy(fileOperation,cCommandInput);
/**Function call to determine operation read/delete/exit/invalid choice and filename*****/
commandInterpretationStatus = interpretCommand(cCommandInput,
inputOperation, inputFileName);
operation = inputOperation;
/**Function call to validate the input command******/
commandValidateStatus = validateCommand(
commandInterpretationStatus, inputOperation, inputFileName);
if(commandValidateStatus==-1)
{
printf("\n Invalid Operation");
}
/*Exit command entered***/
if (commandValidateStatus == 1)
{
/*Code to clear resources */
kill(serverPid,SIGKILL);
kill(clientPid,SIGKILL);
exit(0);
}
/***Read or Delete****/
if (commandValidateStatus == 2 || commandValidateStatus == 3)
{
printf("\n Read or Delete\n");
strcpy(client_MessageBuf.messageText,fileOperation);
client_MessageBuf.messageLength=strlen(fileOperation);
client_MessageBuf.messageType=1;
if((writePIPE(writefd,&client_MessageBuf))<0)
{
printf("\n Error writing on client side ");
}
//read(readfd,*client_MessageBuf,sizeof(client_MessageBuf));
//printf("\n Reding server responsed");
//printf("%s",client_MessageBuf.messageText);
}
}
}
}
int main()
{
int pipe1[2],pipe2[2];
pipe(pipe1);
pipe(pipe2);
pid_t pid;
pid=fork();
serverPid=pid;
if(pid==0)
{
/*Call Server*/
close(pipe1[1]);
close(pipe2[0]);
Server(pipe1[0], pipe2[1]);
}
else
{
close(pipe1[0]);
close(pipe2[1]);
Client(pipe2[0],pipe1[1]);
}
return 0;
}
It looks like the code writes and reads struct msgbuf incorrectly:
typedef struct msgbuf {
int messageLength;
int messageType;
char messageText[MSGBUFFER_SIZE];
} Message_buf;
// ...
strcpy(client_MessageBuf.messageText,fileOperation);
client_MessageBuf.messageLength=strlen(fileOperation);
client_MessageBuf.messageType=1;
if((writePIPE(writefd,&client_MessageBuf))<0)
// ....
int writePIPE(int fd, Message_buf *inputMessage){
printf("\n In write pipe message length :%d",inputMessage->messageLength);
printf("\n In write pipe message Data :%s",inputMessage->messageText);
ssize_t n=write(fd,inputMessage,inputMessage->messageLength);
printf("\n Size :%d", n);
return n;
}
The above pieces that write struct msgbuf only write the first messageLength bytes of the structure which doesn't include the length of messageLength and messageType members, i.e. it truncates the object.
When reading:
ssize_t readPIPE(int fd, Message_buf *outputMessage)
{
// ...
if((n=read(fd,outputMessage,sizeof(outputMessage)))==0)
It reads only sizeof(outputMessage) bytes, which is the size of the pointer, not the object. Even if you fix it by changing it to sizeof(*outputMessage) that won't do enough, since that would expect to read the complete object whereas the writing piece truncates the object.
A good start to fix it would be to split the message into two parts: header and payload. The header is a structure of a fixed size, e.g.:
typedef struct {
int messageType;
int payloadLength;
} MessageHeader;
The payload is a variable-length part following the header. This way it would first write the entire header object into the pipe followed by payloadLength bytes of payload. When reading it would first read again the entire header and then read exactly payloadLength bytes.
Also note, that read() and write() calls may read or write less then asked, so that case needs to be explicitly handled by keeping reading or writing until the exact number of bytes has been processed.
I am not getting ref_count to decrease properly for my GMainContext. The example program here is a small version of a large program (which uses threads, hence the need to create a context and push it on the thread).
GMainLoop *loop;
GMainContext *ctx;
struct conn
{
GSocketClient *client;
GSocketConnection *conn;
GInputStream *in;
GOutputStream *out;
gchar data[8192];
unsigned int count;
};
static void
read_done_cb(GObject *source_object, GAsyncResult *res, gpointer user_data)
{
struct conn *c = (struct conn *)user_data;
gssize len = g_input_stream_read_finish(c->in, res, NULL);
g_input_stream_read_async(c->in, c->data, sizeof c->data / sizeof *c->data, G_PRIORITY_DEFAULT, NULL, read_done_cb, c);
if (c->count++ == 1) {
printf("End of life as I know it...\n");
g_main_loop_quit(loop);
}
}
static void
write_done_cb(GObject *source_object, GAsyncResult *res, gpointer user_data)
{
}
static void
connect_done_cb(GObject *source_object, GAsyncResult *res, gpointer user_data)
{
printf("## %s\n", __FUNCTION__);
struct conn *c = (struct conn *)user_data;
c->conn = g_socket_client_connect_to_host_finish(c->client, res, NULL);
c->in = g_io_stream_get_input_stream(G_IO_STREAM(c->conn));
c->out = g_io_stream_get_output_stream(G_IO_STREAM(c->conn));
char *data = "GET /axis-cgi/mjpg/video.cgi HTTP/1.0\r\n\r\n";
g_output_stream_write_async(c->out, data, strlen(data), G_PRIORITY_DEFAULT, NULL, write_done_cb, c);
g_input_stream_read_async(c->in, c->data, sizeof c->data / sizeof *c->data, G_PRIORITY_DEFAULT, NULL, read_done_cb, c);
}
int
main(int argc, char **argv)
{
g_type_init();
struct conn *c = g_malloc0(sizeof *c);
ctx = g_main_context_new();
loop = g_main_loop_new(ctx, FALSE);
g_main_context_push_thread_default(ctx);
c->client = g_socket_client_new();
g_socket_client_connect_to_host_async(c->client, "10.85.25.20", 80, NULL, connect_done_cb, c);
g_main_loop_run(loop);
g_io_stream_close(G_IO_STREAM(c->conn), NULL, NULL);
g_object_unref(c->client);
g_object_unref(c->conn);
g_main_context_pop_thread_default(ctx);
g_main_loop_unref(loop);
g_main_context_unref(ctx);
return 0;
}
Using gdb, inserting breakpoint just before return I can see that ctx still have one ref count:
(gdb) p ctx->ref_count
$2 = 1
If I do another g_main_context_unref(ctx); everything shuts down as expected. I do not understand where I get this ownership though.
Thanks in advance for your help
I found the error. I read_done_cb I issued another g_input_stream_read_async and immediately after quitting the main loop. g_input_stream_read_async upped the ref_count but GMainLoop never got a chance to return to my callback (and decreasing the ref_count on my GMainContext).
Moving the call to g_input_stream_read_async in my callback to below the if statement
static void
read_done_cb(GObject *source_object, GAsyncResult *res, gpointer user_data)
{
struct conn *c = (struct conn *)user_data;
gssize len = g_input_stream_read_finish(c->in, res, NULL);
if (c->count++ == 1) {
printf("End of life as I know it...\n");
g_main_loop_quit(loop);
}
g_input_stream_read_async(c->in, c->data, sizeof c->data / sizeof *c->data, G_PRIORITY_DEFAULT, NULL, read_done_cb, c);
}
correctly resolved the number of ref counts on my main context.
Silly mistake. Hopefully someone will find some use of my post at least.
g_main_context_new(), g_main_loop_new(), and g_main_context_push_thread_default() all ref the context. g_main_context_pop_thread_default(), g_main_loop_unref(), and g_main_context_unref() all unref it. So your intuition is sound.
I would use a watchpoint in gdb: watch ctx->ref_count to find out where the extra reference is being added.