I have developed a C program that receive can traffics from vcan0 interface.
I would like to add timeout on reception, I mean when a timeout expired (10 seconds for example) with no data received during this time, I print "no data received during 10 seconds" and I make a reboot of my pc(the reboot is made if a specific condition is satisfied).
I have tested with select function I get the timeout but when the specific condition is not satisfied I can't receive can traffics anymore.
should I add something for reactivate reception when I have timeout and specific condition is not satisfied? if yes how?
My program is like this:
...
while(1)
{
FD_ZERO(&set); /* clear the set */
FD_SET(filedesc, &set); /* add our file descriptor to the set */
timeout.tv_sec = 0;
timeout.tv_usec = 10000000; // 10 second
rv = select(fd_max + 1, &set, NULL, NULL, &timeout);
if(rv == -1)
perror("select"); /* an error accured */
else if(rv == 0)
{
printf("no data received within 10 second"); /* a timeout occured */
if (specific condition is true)
{
reboot(RB_AUTOBOOT);
}
}
else
int s;
/* loop on all sockets */
for(i=s;i<=fd_max;i++)
{
read( i, buff, len );
/* some other instruction*/
}
}
...
Related
Is there a way to change the timeout on select() on an FD that's opened for a serial port on the fly? Like, in Thread1, it's set to NULL which means it's going to block until there's any data on the FD. Now, I'd want to change its behavior such that Thread2 sets a timeout on the select in Thread1 which timesout after a specified timeout.
Is it in any way feasible?
Assuming here Thread1 runs first so select() initially starts with no timeout and the timeout is then modified by Thread2 as it runs later (while Thread1 is still waiting on the select())...
int timeout = 5;
struct timeval timeSpec = {timeout, 0};
void *pTimeout = NULL;
void *Thread2(void *)
{
while(1)
{
pTimeout = &timeSpec; // have select() timeout in 5 seconds from now on...
}
}
void *Thread1(void *)
{
fd_set fdset;
while(1)
{
FD_ZERO(&fdset);
FD_SET(fd, &fdset);
ret = select (fd + 1, &fdset, NULL, NULL, pTimeout);
if (ret < 0)
{
// error handling
}
else if (ret == 0)
{
// timeout -- error handling
}
else
{
if (FD_ISSET(fd, &fdset))
{
bytesRead = read(fd, buffer, bytesToRead); // blocking read call
if (ret < 0)
{
// error handling
}
}
}
}
}
I'm initializing a daemon in C in a Debian:
/**
* Initializes the daemon so that mcu.serial would listen in the background
*/
void init_daemon()
{
pid_t process_id = 0;
pid_t sid = 0;
// Create child process
process_id = fork();
// Indication of fork() failure
if (process_id < 0) {
printf("Fork failed!\n");
logger("Fork failed", LOG_LEVEL_ERROR);
exit(1);
}
// PARENT PROCESS. Need to kill it.
if (process_id > 0) {
printf("process_id of child process %i\n", process_id);
exit(0);
}
//unmask the file mode
umask(0);
//set new session
sid = setsid();
if(sid < 0) {
printf("could not set new session");
logger("could not set new session", LOG_LEVEL_ERROR);
exit(1);
}
// Close stdin. stdout and stderr
close(STDIN_FILENO);
close(STDOUT_FILENO);
close(STDERR_FILENO);
}
The main daemon runs in the background and monitors a serial port to communicate with a microcontroller - it reads peripherals (such as button presses) and passes information to it. The main functional loop is
int main(int argc, char *argv[])
{
// We need the port to listen to commands writing
if (argc < 2) {
fprintf(stderr,"ERROR, no port provided\n");
logger("ERROR, no port provided", LOG_LEVEL_ERROR);
exit(1);
}
int portno = atoi(argv[1]);
// Initialize serial port
init_serial();
// Initialize server for listening to socket
init_server(portno);
// Initialize daemon and run the process in the background
init_daemon();
// Timeout for reading socket
fd_set setSerial, setSocket;
struct timeval timeout;
timeout.tv_sec = 0;
timeout.tv_usec = 10000;
char bufferWrite[BUFFER_WRITE_SIZE];
char bufferRead[BUFFER_READ_SIZE];
int n;
int sleep;
int newsockfd;
while (1)
{
// Reset parameters
bzero(bufferWrite, BUFFER_WRITE_SIZE);
bzero(bufferRead, BUFFER_WRITE_SIZE);
FD_ZERO(&setSerial);
FD_SET(fserial, &setSerial);
FD_ZERO(&setSocket);
FD_SET(sockfd, &setSocket);
// Start listening to socket for commands
listen(sockfd,5);
clilen = sizeof(cli_addr);
// Wait for command but timeout
n = select(sockfd + 1, &setSocket, NULL, NULL, &timeout);
if (n == -1) {
// Error. Handled below
}
// This is for READING button
else if (n == 0) {
// This timeout is okay
// This allows us to read the button press as well
// Now read the response, but timeout if nothing returned
n = select(fserial + 1, &setSerial, NULL, NULL, &timeout);
if (n == -1) {
// Error. Handled below
} else if (n == 0) {
// timeout
// This is an okay tiemout; i.e. nothing has happened
} else {
n = read(fserial, bufferRead, sizeof bufferRead);
if (n > 0) {
logger(bufferRead, LOG_LEVEL_INFO);
if (strcmp(stripNewLine(bufferRead), "ev b2") == 0) {
//logger("Shutting down now", LOG_LEVEL_INFO);
system("shutdown -h now");
}
} else {
logger("Could not read button press", LOG_LEVEL_WARN);
}
}
}
// This is for WRITING COMMANDS
else {
// Now read the command
newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
if (newsockfd < 0 || n < 0) logger("Could not accept socket port", LOG_LEVEL_ERROR);
// Now read the command
n = read(newsockfd, bufferWrite, BUFFER_WRITE_SIZE);
if (n < 0) {
logger("Could not read command from socket port", LOG_LEVEL_ERROR);
} else {
//logger(bufferWrite, LOG_LEVEL_INFO);
}
// Write the command to the serial
write(fserial, bufferWrite, strlen(bufferWrite));
sleep = 200 * strlen(bufferWrite) - timeout.tv_usec; // Sleep 200uS/byte
if (sleep > 0) usleep(sleep);
// Now read the response, but timeout if nothing returned
n = select(fserial + 1, &setSerial, NULL, NULL, &timeout);
if (n == -1) {
// Error. Handled below
} else if (n == 0) {
// timeout
sprintf(bufferRead, "err\r\n");
logger("Did not receive response from MCU", LOG_LEVEL_WARN);
} else {
n = read(fserial, bufferRead, sizeof bufferRead);
}
// Error reading from the socket
if (n < 0) {
logger("Could not read response from serial port", LOG_LEVEL_ERROR);
} else {
//logger(bufferRead, LOG_LEVEL_INFO);
}
// Send MCU response to client
n = write(newsockfd, bufferRead, strlen(bufferRead));
if (n < 0) logger("Could not write confirmation to socket port", LOG_LEVEL_ERROR);
}
close(newsockfd);
}
close(sockfd);
return 0;
}
But the CPU usages is always at 100%. Why is that? What can I do?
EDIT
I commented out the entire while loop and made the main function as simple as:
int main(int argc, char *argv[])
{
init_daemon();
while(1) {
// All commented out
}
return 0;
}
And I'm still getting 100% cpu usage
You need to set timeout to the wanted value on every iteration, the struct gets modified on Linux so I think your loop is not pausing except for the first time, i.e. select() is only blocking the very first time.
Try to print tv_sec and tv_usec after select() and see, it's modified to reflect how much time was left before select() returned.
Move this part
timeout.tv_sec = 0;
timeout.tv_usec = 10000;
inside the loop before the select() call and it should work as you expect it to, you can move many delcarations inside the loop too, that would make your code easier to maintan, you could for example move the loop content to a function in the future and that might help.
This is from the linux manual page select(2)
On Linux, select() modifies timeout to reflect the amount of time not slept; most other implementations do not do this. (POSIX.1-2001 permits either behavior.) This causes problems both when Linux code which reads timeout is ported to other operating systems, and when code is ported to Linux that reuses a struct timeval for multiple select()s in a loop without reinitializing it. Consider timeout to be undefined after select() returns.
I think the bold part in the qoute is the important one.
I am trying to write and read data to a serial port file /dev/ttyUSB0, If the operation is unsuccessful for 5 sec I will move ahead. To implement this I chose using the select() system call. However, the exact case in which I am using it seems to not work as expected. Following code:
Simply, I need to check status from 8 devices. So I must write() first a query command. Then wait for a response from the device for timeout seconds.
This procedure should be done for all 8 devices connected on UART.
I am not sure if I must re initialize fdset for using select.
Result: First time select waits for 5 sec timeout. But after that it immediately shows "timeout" without waiting.
struct timeval timeout;
timeout.tv_sec = 5;
timeout.tv_usec = 10;
for(i=0; i <= noOfDevicesDiscovered; i++)
{
if( i < 9 && i > 0)
{
uart_init();
printf("ID: %d\n", i);
address = ((i-1)<<1) | 0x01;
command = 0xA0;
fd_set set;
FD_ZERO(&set);
FD_SET(uart_fd, &set);
write(uart_fd, &address, 1);
write(uart_fd, &command, 1);
rv = select(uart_fd + 1, &set, NULL, NULL, &timeout);
if(rv == -1)
perror("select\n");
else if(rv == 0)
{
printf("timeout\n");
new.level = 0;
new.address = i;
fwrite(&new, sizeof(struct Light_Info), 1, fptr);
continue;
}
else
{
read( uart_fd, &level, 1 );
new.level = level;
}
new.address = i;
fwrite(&new, sizeof(struct Light_Info), 1, fptr);
close(uart_fd);
FD_ZERO(&set);
}
}
How can we solve this.
You need to reinitialise "timeout" after each call of select. From the select man page; "On Linux, select() modifies timeout to reflect the amount of time not slept". So in your case, after the first select call, your timeout values are all 0. Hence subsequent calls to select will timeout immediately.
I am using ioctlsocket() function to make my socket non-blocking but when I call recvfrom(), I get the error 10035 (WSAEWOULDBLOCK).
u_long mode = 1;
ioctlsocket(newSocketIdentifier, FIONBIO, &mode);
while(1)
{
if((recv_len = recvfrom(newSocketIdentifier, receiveBuffer, sizeof(receiveBuffer), 0, (struct sockaddr *) &clientSocket, &clientSocketLength)) == SOCKET_ERROR)
{
char err[128];
itoa(WSAGetLastError(),err,10);
MessageBox( NULL,"Could not Receive Data",err,MB_ICONINFORMATION);
BREAK;
}
}
Can anybody explain why this happens? :(
This is normal if no data is available. The code is WSAEWOULDBLOCK (see this table) and means, that on a blocking port the function would have to sit and wait until it could be served.
while(1)
{
if((recv_len = recvfrom(newSocketIdentifier, receiveBuffer, sizeof(receiveBuffer), 0, (struct sockaddr *) &clientSocket, &clientSocketLength)) == SOCKET_ERROR)
{
int ierr= WSAGetLastError();
if (ierr==WSAEWOULDBLOCK) { // currently no data available
Sleep(50); // wait and try again
continue;
}
// Other errors
char err[128];
itoa(ierr,err,10);
MessageBox( NULL,"Could not Receive Data",err,MB_ICONINFORMATION);
break;
}
}
I cannot agree that this is "normal" like posted above.
In your call of recvfrom you will receive an error in recv_len. I recommend to check that value - it will be SOCKET_ERROR and by calling WSAGetLastErrorenter you will see error WSAEWOULDBLOCK.
I am not a (Windows) socket expert, but based on my tests, I cannot use combination of ioctlsocket and recvfrom for receiving data via UDP in non-blocking mode (I did the same thing like you in your example).
I am planning to use combination of select and recvfrom with minimum possible timeout (1us). I do not know any other possibly better solution now.
Note: you should check also the return value of ioctlsocket for possible error.
I will provide my code sample later today.
UPDATE (adding code as promised):
/* define list of sockets for function select(..) */
fd_set readfds;
/* define timeout for function select(..) */
TIMEVAL tv;
/* timeout: 1us */
tv.tv_usec = 1;
/* timeout: 0s */
tv.tv_sec = 0;
/* just 1 socket is used */
readfds.fd_count = 1;
readfds.fd_array[0] = receivingSocket;
/* determine the status of one or more sockets with timeout */
int selectReturnValue = select(0, &readfds, 0, 0, &tv);
/* check return value of the call of function select(..) */
switch (selectReturnValue)
{
/* select(..) function timeout */
case 0:
/* time limit expired */
break;
/* select(..) function error */
case SOCKET_ERROR:
/* check the error status for the last windows sockets operation */
selectError(WSAGetLastError());
break;
/* no timeout and no error */
default:
/* receive data from UDP */
resultOfrecvfrom = recvfrom(receivingSocket, receivingBuffer, sizeof(receivingBuffer), 0, (SOCKADDR *)&serverReceptionInfo, &serverReceptionInfoLength);
/* check result of call of recvfrom(..) */
switch (resultOfrecvfrom)
{
/* connection has been gracefully closed */
case 0:
/* socket was closed */
break;
/* socket error occurred during last call of socket operation */
case SOCKET_ERROR:
/* check the error status for the last Windows Sockets operation */
recvfromError(WSAGetLastError());
break;
/* resultOfrecvfrom amount of data received */
default:
/* ... add your code here */
break;
}
break;
}
I just copied crucial part of my code if more is needed, let me know in comments.
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
int main ()
{
char name[20];
fd_set input_set;
struct timeval timeout;
int ready_for_reading = 0;
int read_bytes = 0;
/* Empty the FD Set */
FD_ZERO(&input_set );
/* Listen to the input descriptor */
FD_SET(0, &input_set);
/* Waiting for some seconds */
timeout.tv_sec = 10; // 10 seconds
timeout.tv_usec = 0; // 0 milliseconds
/* Invitation for the user to write something */
printf("Enter Username: (in 15 seconds)\n");
printf("Time start now!!!\n");
/* Listening for input stream for any activity */
ready_for_reading = select(1, &input_set, NULL, NULL, &timeout);
/* Here, first parameter is value of the socket descriptor + 1 (STDIN descriptor is 0, so
* 0 +1 = 1)
* in the set, second is our FD set for reading,
* third is the FD set in which any write activity needs to updated, which is not required
* in this case. Fourth is timeout
*/
if (ready_for_reading == -1) {
/* Some error has occured in input */
printf("Unable to read your input\n");
return -1;
} else {
if (ready_for_reading) {
read_bytes = read(0, name, 19);
printf("Read, %d bytes from input : %s \n", read_bytes, name);
} else {
printf(" 10 Seconds are over - no data input \n");
}
}
return 0;
}
How to do the same, but not just once, but in infinite loop which breaks after encountering 'quit' string (for example). Every way I tried - failed.
So if no data has been inputed after 10 seconds program just prints "10 secs are over - no data input" and then starts waiting again. Same after input - just begins again and behave the same every time in infinite loop.
Am little desperate already, please - help.
Thanks.
I don't really see the problem here. Basically just put everything you want in the loop, and let it run. Did you try this?
int main ()
{
/* Declarations and stuff */
/* ... */
/* The loop */
int break_condition = 0;
while (!break_condition)
{
/* Selection */
FD_ZERO(&input_set ); /* Empty the FD Set */
FD_SET(0, &input_set); /* Listen to the input descriptor */
ready_for_reading = select(1, &input_set, NULL, NULL, &timeout);
/* Selection handling */
if (ready_for_reading)
{
/* Do something clever with the input */
}
else
{
/* Handle the error */
}
/* Test the breaking condition */
break_condition = some_calculation();
}
return 0;
}
Note that you have to have keep resetting the selection inside the loop so that it will respond again in the next iteration.
The select() function can be told to block indefinitely by setting timeout to NULL. See select(2) man page:
timeout is an upper bound on the amount of time elapsed before select() returns. If both fields of the timeval stucture are zero, then select() returns immediately. (This is useful for polling.) If timeout is NULL (no timeout), select() can block indefinitely.
So what you want is:
...
ready_for_reading = select(1, &input_set, NULL, NULL, NULL);
...