QProcess outputs with delay threads' stdout/stderr of multithreaded application - linux

Question

My platform:
Ubuntu 17.10 32-bit (Vbox VM)
Qt Creator 3.5.1 (opensource)
Qt 5.5.1 (GCC 4.9.1 20140922 (Red Hat 4.9.1-10), 32 bit
I am trying to invoke a multithreaded program (with arguments) using QProcess.start().
My program runs fine on terminal, i.e. periodically prints on stdout.
Using a TextEdit to log the stdout/stderr of the program I have connected QProcess readyReadStandardOutput/Error signals.
The stdout/stderr that comes from the main thread of the program is correctly shown on the TextEdit, the rest of the output (the one from all the other threads) is not shown.
EDIT
On the main thread an HTTP server is listening.
If a HTTP request is performed by browser at the url "127.0.0.1:32001" (port 32001 is hard coded in the QT code), when the HTTP request is received the program appends the HTTP packet and all the pending output from the other thread (moduleThread) to the TextEdit, so it could be a problem of flushing.
main.c
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/time.h>
#include <sys/signal.h>
#include <sys/stat.h>
#include <sys/types.h>
#include "http_server.h"
static pthread_t moduleThr;
static pthread_attr_t moduleThread_attr;
static bool one_second_elapsed;
static sem_t oneSecondSem;
void *moduleThread(void *arg0)
{
bool one_second_elapsed_local;
while (1)
{
sem_wait(&oneSecondSem);
one_second_elapsed_local = one_second_elapsed;
one_second_elapsed = false;
sem_post(&oneSecondSem);
if (one_second_elapsed_local)
fprintf(stdout, "Hello world each second!\r\n");
usleep(50000);
}
}
static void oneSecElapsed(int signum)
{
sem_wait(&oneSecondSem);
one_second_elapsed = true;
sem_post(&oneSecondSem);
}
static void TIMER_1sec_init(void)
{
struct sigaction sa;
struct itimerval timer;
/* Install timer_handler as the signal handler for SIGALRM. */
memset (&sa, 0, sizeof (sa));
sa.sa_handler = &oneSecElapsed;
sigaction (SIGALRM, &sa, NULL);
/* Configure the timer to expire after 1 sec... */
timer.it_value.tv_sec = 1;
timer.it_value.tv_usec = 0;
/* ... and every 1 sec after that... */
timer.it_interval.tv_sec = 1;
timer.it_interval.tv_usec = 0;
/* Start a virtual timer. It counts down whenever this process is
executing. */
setitimer (ITIMER_REAL, &timer, NULL);
}
/*
* ======== main ========
*/
int main(int argc, char *argv[])
{
const char *tcpport;
if (argc > 2)
{
fprintf(stdout, "id = %s\r\n", argv[1]);
fprintf(stdout, "tcpport = %s\r\n", argv[2]);
tcpport = argv[2];
}
else
exit(-1);
sem_init(&oneSecondSem, 0, 1);
one_second_elapsed = false;
/* Create thread quadro manager */
pthread_attr_init(&moduleThread_attr);
pthread_attr_setstacksize(&moduleThread_attr, 2048);
pthread_create(&moduleThr, &moduleThread_attr, moduleThread, NULL);
TIMER_1sec_init();
HTTPSERVER_init(tcpport);
/* should never return */
return (0);
}
http_server.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h> /* memset() */
#include <stdbool.h>
#include <signal.h>
#include <sys/socket.h>
#include <sys/signal.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include "module.h"
typedef struct { char *name, *value; } header_t;
static header_t reqhdr[17] = { {"\0", "\0"} };
//#define PORT "32001" /* Port to listen on */
#define BACKLOG 10 /* Passed to listen() */
static char *buf;
static char *method; // "GET" or "POST"
static char *uri; // "/index.html" things before '?'
static char *qs; // "a=1&b=2" things after '?'
static char *prot; // "HTTP/1.1"
static char *payload; // for POST
static int payload_size;
// get request header
char *request_header(const char* name)
{
header_t *h = reqhdr;
while(h->name) {
if (strcmp(h->name, name) == 0) return h->value;
h++;
}
return NULL;
}
void handle(int newsock)
{
//static int count = 0;
/* recv(), send(), close() */
int rcvd;
buf = malloc(65535);
rcvd=recv(newsock, buf, 65535, 0);
if (rcvd<0) // receive error
fprintf(stderr,("recv() error\n"));
else if (rcvd==0) // receive socket closed
fprintf(stderr,"Client disconnected unexpectedly.\n");
else // message received
{
buf[rcvd] = '\0';
//fputs(buf, stdout);
//fprintf(stdout, "count = %d\n", count);
method = strtok(buf, " \t\r\n");
uri = strtok(NULL, " \t");
prot = strtok(NULL, " \t\r\n");
fprintf(stderr, "\x1b[32m + [%s] %s\x1b[0m\n", method, uri);
if ((qs = strchr(uri, '?')))
{
*qs++ = '\0'; //split URI
} else {
qs = uri - 1; //use an empty string
}
header_t *h = reqhdr;
char *t = (char *)reqhdr;
char *t2;
while(h < reqhdr+16) {
char *k,*v;
k = strtok(NULL, "\r\n: \t");
if (!k)
break;
v = strtok(NULL, "\r\n");
while(*v && *v==' ')
v++;
h->name = k;
h->value = v;
h++;
fprintf(stderr, "[H] %s: %s\n", k, v);
t = v + 1 + strlen(v);
if (t[1] == '\r' && t[2] == '\n')
break;
}
t+=2;
t++; // now the *t shall be the beginning of user payload
t2 = request_header("content-length"); // and the related header if there is
payload = t;
payload_size = t2 ? atol(t2) : (rcvd-(t-buf));
fprintf(stdout, "-- payload len = %d >", payload_size);
fputs(payload, stdout);
fprintf(stdout, "<\r\n");
if (strcmp(method, "GET") == 0)
{
fprintf(stdout, "\nit's a GET!\r\n");
}
else if (strcmp(method, "POST") == 0)
{
fprintf(stdout, "\nit's a POST!\r\n");
}
sprintf(buf, "HTTP/1.1 200 OK\r\n\r\n");
send(newsock, buf, strlen(buf), 0);
close(newsock);
free(buf);
}
}
int HTTPSERVER_init(const char *tcpport)
{
int sock;
struct addrinfo hints, *res;
int reuseaddr = 1; /* True */
sigset_t sigset, oldset;
sigfillset(&sigset);
pthread_sigmask(SIG_BLOCK, &sigset, &oldset);
/* Get the address info */
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
if (getaddrinfo(NULL, tcpport, &hints, &res) != 0) {
perror("getaddrinfo");
return 1;
}
/* Create the socket */
sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (sock == -1) {
perror("socket");
return 1;
}
/* Enable the socket to reuse the address */
if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &reuseaddr, sizeof(int)) == -1) {
perror("setsockopt");
return 1;
}
/* Bind to the address */
if (bind(sock, res->ai_addr, res->ai_addrlen) == -1) {
perror("bind");
return 1;
}
/* Listen */
if (listen(sock, BACKLOG) == -1) {
perror("listen");
return 1;
}
freeaddrinfo(res);
/* Main loop */
while (1) {
printf("waiting on accept\n");
fflush(stdout);
socklen_t size = sizeof(struct sockaddr_in);
struct sockaddr_in their_addr;
int newsock = accept(sock, (struct sockaddr*)&their_addr, &size);
if (newsock == -1) {
perror("accept");
}
else {
printf("Got a connection from %s on port %d\n",
inet_ntoa(their_addr.sin_addr), htons(their_addr.sin_port));
handle(newsock);
}
}
close(sock);
return 0;
}
As pointed out by #eyllanesc, the pending strings "Hello world each second!\r\n" come out eventually after several seconds.
The moduleThread shoud be a thread and not a different process: this is verified by commadn "ps aux" that shows only "../program/testApp test 32001".
Could any of you kindly give me a hint on what is going on here please?
Thanks for your time,
Francesco