I am working on a MQTT client app in C for an Embedded ARM system that must send message base on GPIO change.
To do this, I have try to launch a pthread that do a epoll_wait and a read on /sys/class/gpio/gpio<x>/value to get the value on change.
First step is the configuration of the gpio as input and edge as both:
root#ad:~# cat /sys/class/gpio/gpio13/direction
in
root#ad:~# cat /sys/class/gpio/gpio13/edge
both
Second step, is the start of the pthread in the main function. (After running the prthread, main will enter in a loop to manage MQTT communication):
// Main
int main(int argc, char *argv[]) {
Network n;
MQTTClient c;
(...)
toStop = false;
pthread_create(&thread_id, NULL, detection, NULL);
while (!toStop)
{
MQTTYield(&c, 100);
(...MQTT stuff...)
}
// stop thread if exists
if(thread_id)
{
pthread_cancel(thread_id);
thread_id = NULL;
}
(...)
}
Then the pthread run the following function:
// detection function call as pthread
void *detection(void *args){
char strvalue[1];
int ret;
int nn;
int ep;
int fd;
struct epoll_event ev, events;
ep = epoll_create1(0);
fd = open("/sys/class/gpio/gpio13/value", O_RDONLY);
nn = read(fd, &strvalue, 1);
if (nn > 0) {
printf("Initial value = %c\n", strvalue[0]);
lseek(fd, 0, SEEK_SET);
}
ev.events = EPOLLIN | EPOLLET; // EPOLLPRI;
ev.data.fd = fd;
ret = epoll_ctl(ep, EPOLL_CTL_ADD, fd, &ev);
printf("ret=%d\n", ret);
while (1)
{
printf("Waiting\n");
ret = epoll_wait(ep, &events, 1, -1);
printf("ret=%d\n", ret);
if(ret > 0) {
lseek(fd, 0, SEEK_SET);
printf("fd=%d\n", events.data.fd);
nn = read(events.data.fd, &strvalue, 1);
printf("nn=%d\n", nn);
printf("value = %c\n", strvalue[0]);
}
}
}
The problem is that when gpio change, epoll_wait got it, but the thread stop during read
Here are the output:
Initial value = 1
ret=0
Waiting
ret=1
fd=7
nn=1
value = 1
Waiting
ret=-1
Waiting
ret=1
fd=7
If I call the function *detection directely in the main (so without pthread), everything is working well.
How to solve this issue ?
Specific issue. thread_id variable name was already used in an other c code included, but compiler dont warning it.
Related
I am new to Linux and I am learning the Linux system calls via the C program. I came up with the function called poll() in the Multiplexed IO topic. I am unable to understand how to write to a specific file and when I tried to write the input into a file, it's writing successfully but no "TIMEOUT" is occurring and the return value of the poll() is "1". Please help with which appropriate flag has to be used in the open() while opening the file. Thanks in advance. Since I am new to this topic, please explain which I misunderstood in this concept. The code which I tried is attached below.
#include<unistd.h>
#include<fcntl.h>
#include<stdio.h>
#include<poll.h>
int main() {
int fd;
int timeout = 5000;
struct pollfd fds[2];
int fd1 = 0;
char buff[11];
while(1) {
fds[0].fd = fd1;
fds[0].events = POLLIN;
fd = open("/home/user/samplefiles/File.txt", O_WRONLY);
fds[1].fd = fd;
fds[1].events = POLLOUT;
int ret = poll(fds, 2, timeout); //returns 1
printf(" Ret = %d\n", ret);
if (ret == 0) {
printf(" Timeout\n");
continue;
}
read(fd1, buff, 10);
write(fd, buff, 10);
printf("written buff = %s\n", buff);
}
}
I have a multiclient Server Socket and I want to block the acces for other Clients, when sending "BEG" to the Server. To open the other Clients again, the Client has to send "END" to the Server. While other Clients are blocked off, they only can use "quit" to exit the Server and if they use conditions() they fall asleep.
So other Clients are blocked for the function conditions() if one process used "BEG", but the process himself has still acces to the function.
If I compile my Code, the Server is running, everything is fine but the Mutexe doesn't work.
The Code is going into the if statement of "BEG" and the Mutex should be locked, but other Clients aren't blocked off.
If I connect a second Client, the Client gets kicked if I use conditions().
My question is, why does the mutex not work for other Clients or in generell? How to check if the Mutex is working?
Edit:
Now my Semaphore doesn't block other processes
Edit 2: I found a way, not the best but one. Now some clients are getting kicked from the Server after using one condition().
main.c:
int state = 0;
int beg() {
state = 1;
return 0;
}
int end() {
state = 0;
return 0;
}
int main() {
int pid, t;
char *eingabe, *inputBuffer[BUFSIZE];
char delimiter[] = "\n ";
int rfd = erstelleSocket();
int cfd;
semaphor semID1 = semGET();
semaphor semID2 = semGET2();
marker[0] = 1;
t = semctl(semID1, 1, SETALL, marker);
if (t == -1) {
fprintf(stderr, "Error with marker\n");
}
t = semctl(semID2, 1, SETALL, marker);
if (t == -1) {
fprintf(stderr, "Error with marker\n");
}
while(1){
cfd = accept(rfd, (struct sockaddr *) &client, &client_len);
if (cfd < 0) {
close(cfd);
fprintf(stderr, "connection failed\n");
break;
}
pid = fork();
if (pid < 0) {
fprintf(stderr, "Error in new process creation\n");
}
if (pid == 0) {
bzero(input, sizeof(input));
bytes_read = read(cfd, input, BUFSIZE);
strncat(input, " ", strlen(" "));
input[strcspn(input, "\r\n")] = 0;
while (bytes_read > 0) {
eingabe = strtok(input, delimiter);
int i = 0;
while (eingabe != NULL) {
inputBuffer[i++] = eingabe;
eingabe = strtok(NULL, delimiter);
}
if (strncmp("quit", inputBuffer[0], 4) == 0) {
close(cfd);
break;
}
if (state != 1) {
down(semID2, 0); //down is a function with semop()
}
down(semID1, 0);
conditions(inputBuffer[0],
inputBuffer[1],
inputBuffer[2],
cfd, semID1, shmID);
up(semID1, 0);
if (state != 1) {
up(semID2, 0); //up is a function with semop()
}
bzero(input, sizeof(input));
bytes_read = read(cfd, input, BUFSIZE);
strncat(input, " ", strlen(" "));
input[strcspn(input, "\r\n")] = 0;
close(rfd);
}
}
close(cfd);
}
close(rfd);
}
my condition function:
void conditions(char *eingabehalter1,
char *eingabehalter2,
char *eingabehalter3,
int cfd, int shmID) {
if (strncmp("PUT", eingabehalter1, 3) == 0) {
put(eingabehalter2, eingabehalter3, cfd, shmID);
} else if (strncmp("GET", eingabehalter1, 3) == 0) {
get(eingabehalter2, cfd, shmID);
} else if (strncmp("DEL", eingabehalter1, 3) == 0) {
del(eingabehalter2, cfd, shmID);
} else if (strncmp("BEG", eingabehalter1, 3) == 0) {
beg();
} else if (strncmp("END", eingabehalter1, 3) == 0) {
end();
} else {
write(cfd, "cmd_nonexistent\n", strlen("cmd_nonexistent\n"));
}
}
createSocket.c:
int rfd; // Rendevouz-Descriptor
rfd = socket(AF_INET, SOCK_STREAM, 0);
int option = 1;
setsockopt(rfd,SOL_SOCKET, SO_REUSEADDR, (const void *) &option, sizeof(int));
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(PORT);
int brt = bind(rfd, (struct sockaddr *) &server, sizeof(server));
int lrt = listen(rfd, 5);
return rfd;
}
main.h:
#include "shmmemory.h"
#include "semaphoren.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <netinet/in.h>
#define PORT 5678
struct sockaddr_in server;
struct sockaddr_in client;
socklen_t client_len;
char input[BUFSIZE];
int bytes_read;
int erstelleSocket();
void conditions(char *eingabehalter1,
char *eingabehalter2,
char *eingabehalter3,
int cfd, int shmID);
int beg();
int end();
unsigned short marker[2];
Your approach cannot work because you're trying to combine fork with threads. fork creates a copy of the parent's address space for each child process, which means that each child process has its own copy of the mutex object. Process-shared mutexes are possible in POSIX, with special attributes, but I suspect even those don't work with fork; they have to be placed in shared memory.
Have you considered creating threads with pthread_create for the service loop? Or else you can implement this entirely using fork (no pthread material). The children can use POSIX named semaphores (sem_open, et al) or possibly, dare I say it, System V IPC.
Also, don't use strtok in multithreaded code, and clearing memory to zero was standardized in 1989's ANSI C as memset(pointer, 0, size). Since that was 31 years ago, it's okay to lay bzero to rest.
The way you initialize the semaphores is wrong for your use case. From the man page of sem_init():
#include <semaphore.h>
int sem_init(sem_t *sem, int pshared, unsigned int value);
If pshared has the value 0, then the semaphore is shared between the
threads of a process, and should be located at some address that is
visible to all threads (e.g., a global variable, or a variable
allocated dynamically on the heap).
If pshared is nonzero, then the semaphore is shared between
processes, and should be located in a region of shared memory
Based on the above explanations from the man page, the things you need change are:
Semaphore declaration
Since you are using semaphores between processes, you need to declare the variable as shared. You can do that via mmap() to create unnamed UNIX semaphore as follows:
sem_t* sem_var = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0)
if (sem_var == MAP_FAILED) // Shared memory creation failed.
goto handle_shm_fail;
Semaphore initialization
Since you are using POSIX semaphores, to make your child use the same semaphores, pshared is set to 1 indicating semaphore is shared between processes.
if (sem_init(sem_var, 1, 1) != 0) // Semaphore initialization failed.
goto handle_sem_fail;
NOTE: In your code sem_var is of type sem_t, now it is a pointer to sem_t. Accordingly, you need to update your code.
Suppose I create a named pipe on a Linux system:
$ mkfifo my_pipe
The next thing I want to do is write a little monitor program which tries to read() from my_pipe, but times out after a while. In the following pseudo-code, I have used a fictional function wait_for_avail(fd, timeout_ms):
int fd = open("my_pipe", O_RDONLY);
while (1) {
//Fictional wait_for_avail(fd, timeout_ms). Is there a real function
//that has this behaviour?
int rc = wait_for_avail(fd, 500);
if (rc == 1) {
char buf[64];
read(fd, buf, 64);
//do something with buf
} else {
fprintf(stderr, "Timed out while reading from my_pipe\n");
//do something else in the program
}
}
I thought poll with the POLLIN flag might work, but it does not. From my simple trials, I have found that it simply waits until another process has opened the named pipe for writing (but not for data to be available, i.e. read() would not block). By the way, for some reason, poll ignores your timeout and just seems to block forever until another process opens the pipe.
The only other solution I can think of is to open() the file with O_NONBLOCK, and sort of manually watch the time going by as I constantly try read()ing with a count of 0 bytes.
Is there a better solution out there?
EDIT: The process I have here blocks on opening the named pipe. However, if you use the O_NONBLOCK flag, the file opens right away. At that point, poll() can be used to wait (with an optional timeout) for the other end of the pipe to be opened for writing.
However, this still does have the behaviour of implementing a timeout for the read() function. It still appears to block as soon as you call read() (even if the pipe was opened with O_NONBLOCK)
Your idea about opening the fifo in non-blocking mode is correct. If you do that, poll()/select()/etc. can be used to wait for the other end to be opened, or timeout first.
The following example program just runs in an infinite loop waiting for other programs to write to my_pipe and echos the written text, with the occasional status update when there's no data or writer:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <poll.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main(void) {
while (1) {
int fd = open("my_pipe", O_RDONLY | O_NONBLOCK);
if (fd < 0) {
perror("open");
return EXIT_FAILURE;
}
struct pollfd waiter = {.fd = fd, .events = POLLIN};
while (1) {
// 10 second timeout
switch (poll(&waiter, 1, 10 * 1000)) {
case 0:
puts("The fifo timed out.");
break;
case 1:
if (waiter.revents & POLLIN) {
char buffer[BUFSIZ];
ssize_t len = read(fd, buffer, sizeof buffer - 1);
if (len < 0) {
perror("read");
return EXIT_FAILURE;
}
buffer[len] = '\0';
printf("Read: %s\n", buffer);
} else if (waiter.revents & POLLERR) {
puts("Got a POLLERR");
return EXIT_FAILURE;
} else if (waiter.revents & POLLHUP) {
// Writer closed its end
goto closed;
}
break;
default:
perror("poll");
return EXIT_FAILURE;
}
}
closed:
if (close(fd) < 0) {
perror("close");
return EXIT_FAILURE;
}
}
}
After a lot of help and patience from #Shawn, I managed to come up with an answer I found satisfying. Here are the contents of a file called pipe_watcher.c:
#include <stdio.h> //printf etc.
#include <errno.h> //errno
#include <string.h> //perror
#include <signal.h> //SIGALRM, sigaction, sigset
#include <time.h> //timer_create, timer_settime
#include <fcntl.h> //open, O_RDONLY
#include <unistd.h> //close
/* This code demonstrates how you can monitor a named pipe with timeouts on the
* read() system call.
*
* Compile with:
*
* gcc -o pipe_watcher pipe_watcher.c -lrt
*
* And run with:
*
* ./pipe_watcher PIPE_FILENAME
*/
//Just needed a dummy handler
void sigalrm_handler(int s) {
return;
}
int main(int argc, char **argv) {
//Check input argument count
if (argc != 2) {
puts("Usage:\n");
puts("\t./pipe_watcher PIPE_FILENAME");
return -1;
}
//Create a timer object
timer_t clk;
int rc = timer_create(CLOCK_REALTIME, NULL, &clk);
if (rc < 0) {
perror("Could not create CLOCK_REALTIME timer");
return -1;
}
//Create some time values for use with timer_settime
struct itimerspec half_second = {
.it_interval = {.tv_sec = 0, .tv_nsec = 0},
.it_value = {.tv_sec = 0, .tv_nsec = 500000000}
};
struct itimerspec stop_timer = {
.it_interval = {.tv_sec = 0, .tv_nsec = 0},
.it_value = {.tv_sec = 0, .tv_nsec = 0}
};
//Set up SIGALRM handler
struct sigaction sigalrm_act = {
.sa_handler = sigalrm_handler,
.sa_flags = 0
};
sigemptyset(&sigalrm_act.sa_mask);
rc = sigaction(SIGALRM, &sigalrm_act, NULL);
if (rc < 0) {
perror("Could not register signal handler");
timer_delete(clk);
return -1;
}
//We deliberately omit O_NONBLOCK, since we want blocking behaviour on
//read(), and we're willing to tolerate dealing with the blocking open()
int fd = open(argv[1], O_RDONLY);
if (fd < 0) {
char msg[80];
sprintf(msg, "Could not open [%s]", argv[1]);
perror(msg);
timer_delete(clk);
return -1;
}
puts("File opened");
while (1) {
//Buffer to read() into
char buf[80];
int len;
//Set up a timer to interrupt the read() call after 0.5 seconds
timer_settime(clk, 0, &half_second, NULL);
//Issue read() system call
len = read(fd, buf, 80);
//Check for errors. The else-if checks for EOF
if (len < 0) {
if (errno == EINTR) {
//This means we got interrupted by the timer; we can keep going
fprintf(stderr, "Timeout, trying again\n");
continue;
} else {
//Something really bad happened. Time to quit.
perror("read() failed");
//No point waiting for the timer anymore
timer_settime(clk, 0, &stop_timer, NULL);
break;
}
} else if (len == 0) {
puts("Reached end of file");
break;
}
//No error or EOF; stop the timer and print the results
timer_settime(clk, 0, &stop_timer, NULL);
write(STDOUT_FILENO, buf, len);
}
//Cleanup after ourselves
timer_delete(clk);
close(fd);
return 0;
}
The technique is to set up a timer before a (blocking) read() call. Then, we can simply check the return value of read() to see if it was interrupted due to a timeout, if a general error occurred, if EOF was reached, or if it successfully read data.
There's only one snag: you can't open the file in non-blocking mode; this causes open() to block until another process opens the pipe for writing. However, in my application this is actually a desirable feature. You could also set up SIGALRM to enforce a timeout on the open(), or maybe do it in another thread.
In fact, this technique should work with any other system call, so I might put together a little helper library to make this pattern easier to use.
EDIT
One more thing: it is very important to not use the SA_RESTART flag when registering the signal handler. Otherwise, even if a system call is interrupted by a signal, Linux will try it again after the signal is handled.
I have a program in c which is supposed to send and receive ipc messages through msgq.
The problem I have is that when I run msgrcv() it sets my global int msqid to 0. And of course I need it at other methods, like in a signal handler.
here is some code:
/* all the includes and some variables*/
#include "msg.h" // include the one I made
int msgQ; // global int
int main(int argc, char *argv[])
{
key = ftok("progfile", 65);
msgQ = msgget(key, 0666 | IPC_CREAT);
printf("msg queue id: %d \n", msgQ);
start_tik_tok(); // setting up the timer and the signal handler
/* irrelevant code */
void read_msgs(msgQ);
}
void read_msgs(int msgQid)
{
while (1)
{
printf("before the read local:%d goval:%d\n", msgQid, msgQ);
int ret = msgrcv(msgQid, &message, sizeof(message), 1, 0);
printf("after the read local:%d global :%d\n", msgQid, msgQ);
if (ret == -1)
/* error handling */
switch (message.action_type)
{
/* mesage handling */
}
}
void signal_handler(int signo)
{
/*I need the global int here to send some messages */
}
void start_tik_tok()
{
//timer interval for setitimer function
struct itimerval timer;
timer.it_interval.tv_sec = 1; //every 1 seconds
timer.it_interval.tv_usec = 0;
timer.it_value.tv_sec = 1; //start in 1 seconds
timer.it_value.tv_usec = 0;
//action for the signal
struct sigaction new_sa;
memset(&new_sa, 0, sizeof(new_sa));
new_sa.sa_handler = &signal_handler;
sigaction(SIGALRM, &new_sa, NULL);
setitimer(ITIMER_REAL, &timer, NULL);
}
the msg.h file:
#include <sys/msg.h>
struct msg_buff{
long mesg_type; //reciver
int sender; //sender
char action_type;
char time_tiks; //time in tiks
} message;
output:
msg queue id: 45416448
before the read local:45416448 global:45416448
after the read local:45416448 global:0
...
you can see that after I run msgrcv(), the value of msgQ turns to 0, even though I'm using a variable to pass the value to the method read_msgs().
The msgrcv function takes a pointer to a structure that starts with a "header" of type long, followed by the message data. The third argument to msgrcv, msgsz, is the size of the message data body, not including the long that's the header. So you should pass something like sizeof message - sizeof(long). By passing sizeof message, you're asking it to overflow the buffer sizeof(long) bytes, and this is clobbering some other global variable.
I found the solution, I'm not sure why is that but it solved it.
I just initialized the int from the beginning.
changed:
int msgQ; // global int
for:
int msgQ = 0; // global int
I am working on a school project where we have to make a multithreaded web server. I am having a problem where when I call sem_wait on my semaphore (which should be initialized to 0 but already seems to be sem_post()ed to 1). I get a SIGABRT.
I am attaching my code below, and I put a comment on the line that is causing my problem. I've spent a few hours with the debugger with little luck.
#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string>
#include <string.h>
#include <iostream>
#include <fcntl.h>
#include <errno.h>
#include <pthread.h>
#include <vector>
#include <semaphore.h>
#include <stdio.h>
#include <cstdlib>
#include <strings.h>
#define PORTNUM 7000
#define NUM_OF_THREADS 5
#define oops(msg) { perror(msg); exit(1);}
#define FCFS 0
#define SJF 1;
void bindAndListen();
void acceptConnection(int socket_file_descriptor);
void* dispatchJobs(void*);
void* replyToClient(void* pos);
//holds ids of worker threads
pthread_t threads[NUM_OF_THREADS];
//mutex variable for sleep_signal_cond
pthread_mutex_t sleep_signal_mutex[NUM_OF_THREADS];
//holds the condition variables to signal when the thread should be unblocked
pthread_cond_t sleep_signal_cond[NUM_OF_THREADS];
//mutex for accessing sleeping_thread_list
pthread_mutex_t sleeping_threads_mutex = PTHREAD_MUTEX_INITIALIZER;
//list of which threads are sleeping so they can be signaled and given a job
std::vector<bool> *sleeping_threads_list = new std::vector<bool>();
//number of threads ready for jobs
sem_t available_threads;
sem_t waiting_jobs;
//holds requests waiting to be given to one of the threads for execution
//request implemented as int[3] with int[0]== socket_descriptor int[1]== file_size int[2]== file_descriptor of requested file
//if file_size == 0 then HEAD request
std::vector<std::vector<int> >* jobs = new std::vector<std::vector<int> >();
pthread_mutex_t jobs_mutex = PTHREAD_MUTEX_INITIALIZER;
int main (int argc, char * const argv[]) {
//holds id for thread responsible for removing jobs from ready queue and assigning them to worker thread
pthread_t dispatcher_thread;
//initializes semaphores
if(sem_init(&available_threads, 0, NUM_OF_THREADS) != 0){
oops("Error Initializing Semaphore");
}
if(sem_init(&waiting_jobs, 0, 0) !=0){
oops("Error Initializing Semaphore");
}
//initializes condition variables and guarding mutexes
for(int i=0; i<NUM_OF_THREADS; i++){
pthread_cond_init(&sleep_signal_cond[i], NULL);
pthread_mutex_init(&sleep_signal_mutex[i], NULL);
}
if(pthread_create(&dispatcher_thread, NULL, dispatchJobs, (void*)NULL) !=0){
oops("Error Creating Distributer Thread");
}
for (int i=0; i<NUM_OF_THREADS; i++) {
pthread_mutex_lock(&sleeping_threads_mutex);
printf("before");
sleeping_threads_list->push_back(true);
printf("after");
pthread_mutex_unlock(&sleeping_threads_mutex);
}
printf("here");
for (int i=0; i<NUM_OF_THREADS; i++) {
//creates threads and stores ID in threads
if(pthread_create(&threads[i], NULL, replyToClient, (void*)i) !=0){
oops("Error Creating Thread");
}
}
/*
if(sem_init(&available_threads, 0, NUM_OF_THREADS) !=0){
oops("Error Initializing Semaphore");
}
if(sem_init(&waiting_jobs, 0, 0) !=0){ //this is the semaphore thats used in the sem_wait
oops("Error Initializing Semaphore");
}*/
bindAndListen();
}
//binds to socket and listens for connections
//being done by main thead
void bindAndListen(){
struct sockaddr_in saddr;
struct hostent *hp;
char hostname[256];
int sock_id, sock_fd;
gethostname(hostname, 256);
hp = gethostbyname(hostname);
bzero(&saddr, sizeof(saddr));
//errno = 0;
bcopy(hp->h_addr, &saddr.sin_addr, hp->h_length);
saddr.sin_family = AF_INET;
saddr.sin_port = htons(PORTNUM);
saddr.sin_addr.s_addr = INADDR_ANY;
sock_id = socket(AF_INET, SOCK_STREAM, 0);
if(sock_id == -1){
oops("socket");
printf("socket");
}
if(bind(sock_id, (const sockaddr*)&saddr, sizeof(saddr)) ==0){
if(listen(sock_id, 5) ==-1){
oops("listen");
}
//each time a new connection is accepted, get file info and push to ready queue
while(1){
int addrlen = sizeof(saddr);
sock_fd = accept(sock_id, (sockaddr*)&saddr, (socklen_t*)&addrlen);
if (sock_fd > 0) {
acceptConnection(sock_fd);
}else {
oops("Error Accepting Connection");
}
}
}else{
oops("there was an error binding to socket");
}
}// end of bindAndListen()
//accepts connection and gets file info of requested file
//being done by main thread
void acceptConnection(int sock_fd){
printf("**Server: A new client connected!");
//only using loop so on error we can break out on error
while(true){
//used to hold input from client
char* inputBuff = new char[BUFSIZ];
int slen = read(sock_fd, inputBuff, BUFSIZ);
//will sit on space between HEAD/GET and path
int pos1 = 0;
//will sit on space between path and HTTP version
int pos2 = 0;
//need duplicate ptr so we can manipulate one in the loop
char* buffPtr = inputBuff;
//parses client input breaks up query by spaces
for(int i=0; i<slen; i++){
if(*buffPtr == ' '){
if (pos1 == 0) {
pos1 = i;
}else {
pos2 = i;
break;
}
}
buffPtr++;
}
if((pos1 - pos2) >=0){
std::string str = "Invalid Query";
write(sock_fd, str.c_str(), strlen(str.c_str()));
break;
}
printf("slen length %d\n", slen);
std::string* method = new std::string(inputBuff, pos1);
printf("method length %lu\n",method->length());
//increment the ptr for buff to the starting pos of the path
inputBuff += ++pos1;
printf("pos2 - pos1 %d\n", (pos2 - pos1));
printf("pos1 = %d pos2 = %d\n", pos1, pos2);
std::string* path = new std::string(inputBuff, (pos2 - pos1));
printf("path length %lu\n", path->length());
printf("part1 %s\n", method->c_str());
printf("part2 %s\n", path->c_str());
//opens file requested by client
int fd = open(path->c_str(), O_RDONLY);
if(fd < 0){
std::string* error = new std::string("Error Opening File");
*error += *path + std::string(strerror(errno), strlen(strerror(errno)));
write(sock_fd, error->c_str(), strlen(error->c_str()));
break;
}
int file_size;
if(method->compare("GET") == 0){
//gets file info and puts the resulting struct in file_info
struct stat file_info;
if(fstat(fd, &file_info) !=0){
oops("Error getting file info");
}
file_size = file_info.st_size;
}else if(method->compare("HEAD")){
file_size = 0;
}else{
write(sock_fd, "Invalid Query", strlen("Invalid Query"));
break;
}
//job to be pushed to ready queue
std::vector<int> job;
job.push_back(sock_fd);
job.push_back(file_size);
job.push_back(fd);
//check mutex guarding the ready queue
pthread_mutex_lock(&jobs_mutex);
//push job to back of ready queue
jobs->push_back(job);
//unlock mutex guarding the ready queue
pthread_mutex_unlock(&jobs_mutex);
//increment number of jobs in ready queue
sem_post(&waiting_jobs);
} //end of while(true)
// we only end up here if there was an error
fflush(stdout);
close(sock_fd);
}// end of acceptConnection()
//routine run by dispather thread
void *dispatchJobs(void*){
while(true){
//wait for a thread to be available to execute a job
sem_wait(&available_threads);
//wait for a job to be waiting in the ready queue
sem_wait(&waiting_jobs); //this is the line thats crashing
//aquire lock to check which threads are waiting
pthread_mutex_lock(&sleeping_threads_mutex);
//go through list of threads to see which is waiting
for(int i=0; i<sleeping_threads_list->size(); i++){
if(sleeping_threads_list->at(i)){
//unlocks lock for access to list of waiting threads
pthread_mutex_unlock(&sleeping_threads_mutex);
//allows us access to the list of condition variables to signal the thread to resume execution
pthread_mutex_lock(&sleep_signal_mutex[i]);
pthread_cond_signal(&sleep_signal_cond[i]);
pthread_mutex_unlock(&sleep_signal_mutex[i]);
}
}
}//end of while(true)
}//end of dispatchJobs()
//sends file or metadata to client
//run by worker thread
//pos is position of condition variable that it waits to be signaled in the sleep_signal_cond[] array
void* replyToClient(void* pos){
int position = (long)pos;
while(true){
//waits for dispather thread to signal it
pthread_mutex_lock(&sleep_signal_mutex[position]);
pthread_cond_wait(&sleep_signal_cond[position], &sleep_signal_mutex[position]);
pthread_mutex_unlock(&sleep_signal_mutex[position]);
//lock mutex to get job to be executed
pthread_mutex_lock(&jobs_mutex);
std::vector<int> job = jobs->front();
//removes job from front of vector
jobs->erase(jobs->begin());
//releases mutex
pthread_mutex_unlock(&jobs_mutex);
//socket file descriptor, used for writing to socket
int sock_fd =job[0];
int file_size = job[1];
//file descriptor for requested job
int fd = job[2];
//holds output to be written to socket
char* outputBuffer = new char[BUFSIZ];
//GET request, send file
if(file_size !=0){
int readResult = 0;
while ((readResult = read(fd, outputBuffer, BUFSIZ)) > 0) {
if(write(sock_fd, outputBuffer, readResult) != readResult){
printf("We may have a write error");
}
}
if(readResult < 0){
oops("Error Reading File");
}
if(readResult == 0){
printf("finished sending file");
}
}else{ // HEAD request
}
//increment number of available threads
sem_post(&available_threads);
}
}// end of replyToClient()
Check again the whole logic of the code - it is possible to reach here:
pthread_mutex_lock(&jobs_mutex);
std::vector<int> job = jobs->front();
//removes job from front of vector
jobs->erase(jobs->begin());
//releases mutex
pthread_mutex_unlock(&jobs_mutex);
with jobs->size () == 0, in which case front() and erase() invoke undefined behavior, which may well result in the effects you observe.
Check whether your program still crashes after the following change:
//lock mutex to get job to be executed
pthread_mutex_lock(&jobs_mutex);
if (jobs->size () == 0)
{
pthread_mutex_unlock (&jobs_mutex);
continue;
}
std::vector<int> job = jobs->front();
//removes job from front of vector
jobs->erase(jobs->begin());
//releases mutex
pthread_mutex_unlock(&jobs_mutex);
I haven't used POSIX semaphores, but I believe this is what is happening. I'm only familiar with Linux kernel semaphores, and you don't mention your system. The init function's 3rd parameter probably sets the count variable. You set it to 0 (= busy but no other processes waiting). The wait function probably invokes down(), which begins by decreasing the count variable by 1: to -1, which means the semaphore you mean to use is locked now. There is nothing in your program to ever unlock it I believe (from browsing your code - it's pretty long), so you are in trouble. Try setting it to 1 in init. This might be all that is needed.