C beginner here. The function send_chars_to_reducers does not appeared to be getting called inside the forked processes created in fork_mappers function.
C Code
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#define BUFFER_SIZE 1024
#define ALPHA_OFFSET 97
#define LETTERS 26
const int NUM_OF_MAPPERS = 4;
const int NUM_OF_REDUCERS = 26;
const int PIPE_READ_END = 0;
const int PIPE_WRITE_END = 1;
const int PIPE_BUFFER_SIZE = 1000;
int mapper_pipes[4][2];
int reducer_pipes[26][2];
void pipe_wrapper(int pipefd[]) {
int ret = pipe(pipefd);
if (ret == -1) {
perror("Error. Failed when trying to create pipes.");
exit(EXIT_FAILURE);
}
}
void create_mapper_pipes(void) {
int i;
for (i = 0; i < NUM_OF_MAPPERS; i++) {
pipe_wrapper(mapper_pipes[i]);
}
}
void create_reducer_pipes(void) {
int i;
for (i=0; i < NUM_OF_REDUCERS; i++) {
pipe_wrapper(reducer_pipes[i]);
}
}
// Prints an error msg and exits if one occurs. Else, returns the system call value.
int print_if_err(int syscall_val, const char* syscall_name) {
if (syscall_val < 0) {
perror(syscall_name);
exit(errno);
} else {
//No syscall error we can return
return syscall_val;
}
}
void send_chars_to_reducers(void) {
printf("hello from send_chars_to_reducers\n");
}
void fork_mappers(void) {
/* Constants useful to all children */
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i=0; i<NUM_OF_MAPPERS; i++) {
pid_t mapper_pid = print_if_err(fork(), "fork");
close(mapper_pipes[i][PIPE_WRITE_END]);
if (mapper_pid == 0) {
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
while(rlen > 0) {
send_chars_to_reducers();
printf("read line from forked_mappers, p%d: %s\n", i, ibuf);
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
}
_exit(0);
}
}
}
void fork_reducers(void) {
printf("hello from fork_reducers\n");
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
while (1 == 1) {
}
}
}
}
void send_lines_to_mappers(void) {
int wlen = 0;
char obuf[PIPE_BUFFER_SIZE];
int ob_size;
int count = 0;
char buff[BUFFER_SIZE]; // a buffer for each line of the file
FILE *input_file = fopen("input.txt", "r");
// read the input file line by line
while(fgets(buff, BUFFER_SIZE, input_file) > 0) {
printf("read line from send_lin_to_mappers: %s\n", buff);
ob_size = sizeof buff;
switch(count) {
case 0 :
write(mapper_pipes[0][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[0][PIPE_WRITE_END]);
break;
case 1 :
write(mapper_pipes[1][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[1][PIPE_WRITE_END]);
break;
case 2 :
write(mapper_pipes[2][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[2][PIPE_WRITE_END]);
break;
case 3 :
write(mapper_pipes[3][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[3][PIPE_WRITE_END]);
break;
default :
printf("you did something wrong in send_lines_to_mappers loop");
}
count++;
}
fclose(input_file);
}
int main(void) {
// Setup the mapper pipes
create_mapper_pipes();
create_reducer_pipes();
fork_reducers();
fork_mappers();
send_lines_to_mappers();
return 0;
}
Output
hello from fork_reducers
read line from send_lin_to_mappers: I like coding in C.
read line from send_lin_to_mappers: I like manually allocating memory, and opening the registers window in Visual Studio to see the values of the eax register and blitting graphics to the screen and all the stuff that Dr. Dobbs wrote about in the 90s.
read line from send_lin_to_mappers: My programming friends seem to believe that understanding this level of programming is good in a hand-wavy, theoretical sense, but when you consider all the web development, Java frameworks, and existing libraries most programmers today rely on, it's hard to really pin down a solid answer to the question "Why learn C?"
read line from send_lin_to_mappers: This is my attempt to answer that question, and I believe it comes down to the basic programming concept of abstraction.
The problem is the number of processes which share handles.
Each reducer has the pipes open
Each mapper has the pipes open, so the pipes are never properly closed ( the reducers are in a busy loop.
if (mapper_pid == 0) {
int j;
for( j = 0; j < NUM_OF_MAPPERS; j++ ){
close( mapper_pipes[j][PIPE_WRITE_END]);
if( j != i ){
close(mapper_pipes[j][PIPE_READ_END]);
}
}
I commented out the reducer fork's and then fixed the mapper forks to close all the pipe handles in the child except the one we want to read from.
This started to make the program work.
From pipe documentation, you should close the unused bits of a pipe. But you have pre-opened all the pipes (probably better localizing them), and have therefore got to close all the unused handles in the sub-processes to have the OS tidy up the resource correctly
Related
C beginner here. My C program is supposed to read a file input.txt line by line and then write a line to one of the mapper_pipes. There are four lines of text and each line gets sent to a different mapper pipe. 4 processes are forked, one for each of the lines of text. The program is properly reading the lines of text from the file, I know because I console log them in the send_line_to_mapper function. The code inside the mapper forks which seem to be working since printf("hello from mapper/n"); prints but it does not print the messages sent through the pipe here printf("forked mapper read line: %s\n", ibuf);. Appreciate any help.
Update 2
*Edit: I moved close to immediatly after fork and now its working.
Closed write end of the pipe after writing to pipe and after forking process that reads from pipe, still not reading EOF.
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#define BUFFER_SIZE 1024
#define ALPHA_OFFSET 97
#define LETTERS 26
const int NUM_OF_MAPPERS = 4;
const int NUM_OF_REDUCERS = 26;
const int PIPE_READ_END = 0;
const int PIPE_WRITE_END = 1;
const int PIPE_BUFFER_SIZE = 1000;
int mapper_pipes[4][2];
int reducer_pipes[26][2];
void pipe_wrapper(int pipefd[]) {
int ret = pipe(pipefd);
if (ret == -1) {
perror("Error. Failed when trying to create pipes.");
exit(EXIT_FAILURE);
}
}
void create_mapper_pipes(void) {
int i;
for (i = 0; i < NUM_OF_MAPPERS; i++) {
pipe_wrapper(mapper_pipes[i]);
}
}
void create_reducer_pipes(void) {
int i;
for (i=0; i < NUM_OF_REDUCERS; i++) {
pipe_wrapper(reducer_pipes[i]);
}
}
// Prints an error msg and exits if one occurs. Else, returns the system call value.
int print_if_err(int syscall_val, const char* syscall_name) {
if (syscall_val < 0) {
perror(syscall_name);
exit(errno);
} else {
//No syscall error we can return
return syscall_val;
}
}
void fork_mappers(void) {
/* Constants useful to all children */
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i=0; i<NUM_OF_MAPPERS; i++) {
pid_t mapper_pid = print_if_err(fork(), "fork");
if (mapper_pid == 0) {
close(mapper_pipes[i][PIPE_WRITE_END]);
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
while(rlen > 0) {
printf("read line from forked_mappers, p%d: %s\n", i, ibuf);
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
}
_exit(0);
}
}
}
void fork_reducers(void) {
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
}
}
}
void send_lines_to_mappers(void) {
int wlen = 0;
char obuf[PIPE_BUFFER_SIZE];
int ob_size;
int count = 0;
char buff[BUFFER_SIZE]; // a buffer for each line of the file
FILE *input_file = fopen("input.txt", "r");
// read the input file line by line
while(fgets(buff, BUFFER_SIZE, input_file) > 0) {
printf("read line from send_lin_to_mappers: %s\n", buff);
ob_size = sizeof buff;
switch(count) {
case 0 :
write(mapper_pipes[0][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[0][PIPE_WRITE_END]);
break;
case 1 :
write(mapper_pipes[1][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[1][PIPE_WRITE_END]);
break;
case 2 :
write(mapper_pipes[2][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[2][PIPE_WRITE_END]);
break;
case 3 :
write(mapper_pipes[3][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[3][PIPE_WRITE_END]);
break;
default :
printf("you did something wrong in send_lines_to_mappers loop");
}
count++;
}
fclose(input_file);
}
int main(void) {
// Setup the mapper pipes
create_mapper_pipes();
create_reducer_pipes();
fork_mappers();
//fork_reducers();
send_lines_to_mappers();
return 0;
}
Updated Code After Help From Comments
Now everything seems to be working but forked processes in fork_mappers never leave while loop and exit.
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#define BUFFER_SIZE 1024
#define ALPHA_OFFSET 97
#define LETTERS 26
const int NUM_OF_MAPPERS = 4;
const int NUM_OF_REDUCERS = 26;
const int PIPE_READ_END = 0;
const int PIPE_WRITE_END = 1;
const int PIPE_BUFFER_SIZE = 1000;
int mapper_pipes[4][2];
int reducer_pipes[26][2];
void pipe_wrapper(int pipefd[]) {
int ret = pipe(pipefd);
if (ret == -1) {
perror("Error. Failed when trying to create pipes.");
exit(EXIT_FAILURE);
}
}
void create_mapper_pipes(void) {
int i;
for (i = 0; i < NUM_OF_MAPPERS; i++) {
pipe_wrapper(mapper_pipes[i]);
}
}
void create_reducer_pipes(void) {
int i;
for (i=0; i < NUM_OF_REDUCERS; i++) {
pipe_wrapper(reducer_pipes[i]);
}
}
// Prints an error msg and exits if one occurs. Else, returns the system call value.
int print_if_err(int syscall_val, const char* syscall_name) {
if (syscall_val < 0) {
perror(syscall_name);
exit(errno);
} else {
//No syscall error we can return
return syscall_val;
}
}
void fork_mappers(void) {
/* Constants useful to all children */
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i=0; i<NUM_OF_MAPPERS; i++) {
pid_t mapper_pid = print_if_err(fork(), "fork");
if (mapper_pid == 0) {
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
while(rlen > 0) {
printf("read line from forked_mappers, p%d: %s\n", i, ibuf);
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
}
_exit(0);
}
}
}
void fork_reducers(void) {
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
}
}
}
void send_lines_to_mappers(void) {
int wlen = 0;
char obuf[PIPE_BUFFER_SIZE];
int ob_size;
int count = 0;
char buff[BUFFER_SIZE]; // a buffer for each line of the file
FILE *input_file = fopen("input.txt", "r");
// read the input file line by line
while(fgets(buff, BUFFER_SIZE, input_file) > 0) {
printf("read line from send_lin_to_mappers: %s\n", buff);
ob_size = sizeof buff;
switch(count) {
case 0 :
write(mapper_pipes[0][PIPE_WRITE_END], buff, ob_size);
break;
case 1 :
write(mapper_pipes[1][PIPE_WRITE_END], buff, ob_size);
break;
case 2 :
write(mapper_pipes[2][PIPE_WRITE_END], buff, ob_size);
break;
case 3 :
write(mapper_pipes[3][PIPE_WRITE_END], buff, ob_size);
break;
default :
printf("you did something wrong in send_lines_to_mappers loop");
}
count++;
}
fclose(input_file);
}
int main(void) {
// Setup the mapper pipes
create_mapper_pipes();
create_reducer_pipes();
fork_mappers();
//fork_reducers();
send_lines_to_mappers();
return 0;
}
C Code
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#define BUFFER_SIZE 1024
#define ALPHA_OFFSET 97
#define LETTERS 26
const int NUM_OF_MAPPERS = 4;
const int NUM_OF_REDUCERS = 26;
const int PIPE_READ_END = 0;
const int PIPE_WRITE_END = 1;
const int PIPE_BUFFER_SIZE = 32;
int mapper_pipes[4][2];
int reducer_pipes[26][2];
void pipe_wrapper(int pipefd[]) {
int ret = pipe(pipefd);
if (ret == -1) {
perror("Error. Failed when trying to create pipes.");
exit(EXIT_FAILURE);
}
}
void create_mapper_pipes(void) {
int i;
for (i = 0; i < NUM_OF_MAPPERS; i++) {
pipe_wrapper(mapper_pipes[i]);
}
}
void create_reducer_pipes(void) {
int i;
for (i=0; i < NUM_OF_REDUCERS; i++) {
pipe_wrapper(reducer_pipes[i]);
}
}
// Prints an error msg and exits if one occurs. Else, returns the system call value.
int print_if_err(int syscall_val, const char* syscall_name) {
if (syscall_val < 0) {
perror(syscall_name);
exit(errno);
} else {
//No syscall error we can return
return syscall_val;
}
}
void fork_mappers(void) {
/* Constants useful to all children */
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i=0; i<NUM_OF_MAPPERS; i++) {
pid_t mapper_pid = print_if_err(fork(), "fork");
printf("%d\n", mapper_pid);
if (mapper_pid == 0) {
printf("hello from mapper/n");
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
while(rlen > 0) {
printf("forked mapper read line: %s\n", ibuf);
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
}
_exit(0);
}
}
}
void fork_reducers(void) {
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
}
}
}
void send_lines_to_mappers(void) {
int wlen = 0;
char obuf[PIPE_BUFFER_SIZE];
int obptr = 0;
int count = 0;
char buff[BUFFER_SIZE]; // a buffer for each line of the file
FILE *input_file = fopen("input.txt", "r");
// read the input file line by line
while(fgets(buff, BUFFER_SIZE, input_file) > 0) {
printf("read line: %s\n", buff);
switch(count) {
case 0 :
write(mapper_pipes[0][PIPE_WRITE_END], obuf, obptr);
break;
case 1 :
write(mapper_pipes[1][PIPE_WRITE_END], obuf, obptr);
break;
case 2 :
write(mapper_pipes[2][PIPE_WRITE_END], obuf, obptr);
break;
case 3 :
write(mapper_pipes[3][PIPE_WRITE_END], obuf, obptr);
break;
default :
printf("you did something wrong in send_lines_to_mappers loop");
}
count++;
}
fclose(input_file);
}
int main(void) {
// Setup the mapper pipes
create_mapper_pipes();
create_reducer_pipes();
fork_mappers();
//fork_reducers();
send_lines_to_mappers();
return 0;
}
Output
9592
9593
9594
9595
read line: I like coding in C.
read line: I like manually allocating memory, and opening the registers window in Visual Studio to see the values of the eax register and blitting graphics to the screen and all the stuff that Dr. Dobbs wrote about in the 90s.
read line: My programming friends seem to believe that understanding this level of programming is good in a hand-wavy, theoretical sense, but when you consider all the web development, Java frameworks, and existing libraries most programmers today rely on, it's hard to really pin down a solid answer to the question "Why learn C?"
read line: This is my attempt to answer that question, and I believe it comes down to the basic programming concept of abstraction.
0
0
0
0
Trying to give a Minimal Viable Example of the problem. Basically the method send_chars_to_reducers sends a character to the proper reducer_pipe. The fork_reducers function remains in its while loop until it receives EOF but it never does even though I close all reducer pipes in send_chars_to_reducers. I know it doesnt exit the while loop because it never prints exiting reducers.
C Code
void send_chars_to_reducers(char * line) {
printf("SEND_CHARS_TO_REDUCERS read: %s\n\n", line);
int i;
int ob_size = 1;
int wlen = 0;
for (i = 0; i < strlen(line); i++) {
if (line[i] >= ALPHA_OFFSET && line[i] < ALPHA_OFFSET + LETTERS) {
int pipe_num = line[i] - ALPHA_OFFSET;
printf("SENDING %c TO REDUCER PIPE %d\n", line[i], pipe_num);
wlen = print_if_err(write(reducer_pipes[pipe_num][PIPE_WRITE_END], &line[i], ob_size), "write");
printf("WROTE %s to REDUCER %d\n", line[i], i);
}
}
close_reducer_pipes();
}
void close_reducer_pipes(void) {
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
close(reducer_pipes[i][PIPE_WRITE_END]);
close(reducer_pipes[i][PIPE_READ_END]);
}
}
void fork_mappers(void) {
/* Constants useful to all children */
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i=0; i<NUM_OF_MAPPERS; i++) {
pid_t mapper_pid = print_if_err(fork(), "fork");
if (mapper_pid == 0) {
int j;
for (j=0; j < NUM_OF_MAPPERS; j++) {
close(mapper_pipes[i][PIPE_WRITE_END]);
if (j != i) {
close(mapper_pipes[j][PIPE_READ_END]);
}
}
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
send_chars_to_reducers(ibuf);
close_reducer_pipes();
//printf("forked mapper%d read: %s\n\n", i, ibuf);
close(mapper_pipes[i][PIPE_READ_END]);
_exit(0);
}
}
}
void fork_reducers(void) {
printf("HELLLOOOO FROM REDUCER\n");
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
while (1) {
rlen = print_if_err(read(reducer_pipes[i][PIPE_READ_END], ibuf, 1), "read");
if (rlen > 0) {
printf("REDUCER #%d, read %s\n", i, ibuf);
} else {
break;
}
}
printf("exiting reducer\n");
_exit(0);
}
}
}
Entire C Code
#include <sys/wait.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#define BUFFER_SIZE 1024
#define ALPHA_OFFSET 97
#define LETTERS 26
const int NUM_OF_MAPPERS = 4;
const int NUM_OF_REDUCERS = 26;
const int PIPE_READ_END = 0;
const int PIPE_WRITE_END = 1;
const int PIPE_BUFFER_SIZE = 1000;
int mapper_pipes[4][2];
int reducer_pipes[26][2];
int letter_count[26];
void init_letter_count(void) {
int i;
for (i =0; i < 26; i++) {
letter_count[i] = 0;
}
}
void pipe_wrapper(int pipefd[]) {
int ret = pipe(pipefd);
if (ret == -1) {
perror("Error. Failed when trying to create pipes.");
exit(EXIT_FAILURE);
}
}
void create_mapper_pipes(void) {
int i;
for (i = 0; i < NUM_OF_MAPPERS; i++) {
pipe_wrapper(mapper_pipes[i]);
}
}
void create_reducer_pipes(void) {
int i;
for (i=0; i < NUM_OF_REDUCERS; i++) {
pipe_wrapper(reducer_pipes[i]);
}
}
// Prints an error msg and exits if one occurs. Else, returns the system call value.
int print_if_err(int syscall_val, const char* syscall_name) {
if (syscall_val < 0) {
perror(syscall_name);
exit(errno);
} else {
//No syscall error we can return
return syscall_val;
}
}
void send_chars_to_reducers(char * line) {
printf("SEND_CHARS_TO_REDUCERS read: %s\n\n", line);
int i;
int ob_size = 1;
int wlen = 0;
for (i = 0; i < strlen(line); i++) {
if (line[i] >= ALPHA_OFFSET && line[i] < ALPHA_OFFSET + LETTERS) {
int pipe_num = line[i] - ALPHA_OFFSET;
printf("SENDING %c TO REDUCER PIPE %d\n", line[i], pipe_num);
wlen = print_if_err(write(reducer_pipes[pipe_num][PIPE_WRITE_END], &line[i], ob_size), "write");
printf("WROTE %c to REDUCER %d\n", line[i], pipe_num);
}
}
printf("END OF SEND CHAR FOR LOOP");
close_reducer_pipes();
}
void close_reducer_pipes(void) {
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
print_if_err(close(reducer_pipes[i][PIPE_WRITE_END]), "close");
print_if_err(close(reducer_pipes[i][PIPE_READ_END]), "close");
}
}
void fork_mappers(void) {
/* Constants useful to all children */
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i=0; i<NUM_OF_MAPPERS; i++) {
pid_t mapper_pid = print_if_err(fork(), "fork");
if (mapper_pid == 0) {
int j;
for (j=0; j < NUM_OF_MAPPERS; j++) {
close(mapper_pipes[i][PIPE_WRITE_END]);
if (j != i) {
close(mapper_pipes[j][PIPE_READ_END]);
}
}
rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
send_chars_to_reducers(ibuf);
//printf("forked mapper%d read: %s\n\n", i, ibuf);
close(mapper_pipes[i][PIPE_READ_END]);
_exit(0);
}
}
}
void fork_reducers(void) {
printf("HELLLOOOO FROM REDUCER\n");
char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer
int rlen = 0;
int i;
for (i = 0; i < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
while (1) {
rlen = print_if_err(read(reducer_pipes[i][PIPE_READ_END], ibuf, 1), "read");
printf("RLEN = %d\n", rlen);
if (rlen > 0) {
int letter_count_i = ibuf[0] - ALPHA_OFFSET;
printf("REDUCER #%d, read %s, letter_count_i = %d\n", i, ibuf, letter_count_i);
letter_count[letter_count_i]++;
} else {
break;
}
}
printf("REDUCER EXITING\n");
_exit(0);
}
}
}
void send_lines_to_mappers(void) {
int wlen = 0;
char obuf[PIPE_BUFFER_SIZE];
int ob_size;
int count = 0;
char buff[BUFFER_SIZE]; // a buffer for each line of the file
FILE *input_file = fopen("input.txt", "r");
// read the input file line by line
while(fgets(buff, BUFFER_SIZE, input_file) > 0) {
//printf("send_lines_to_mappers read: %s\n\n", buff);
ob_size = sizeof buff;
switch(count) {
case 0 :
write(mapper_pipes[0][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[0][PIPE_WRITE_END]);
close(mapper_pipes[0][PIPE_READ_END]);
break;
case 1 :
write(mapper_pipes[1][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[1][PIPE_WRITE_END]);
close(mapper_pipes[1][PIPE_READ_END]);
break;
case 2 :
write(mapper_pipes[2][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[2][PIPE_WRITE_END]);
close(mapper_pipes[2][PIPE_READ_END]);
break;
case 3 :
write(mapper_pipes[3][PIPE_WRITE_END], buff, ob_size);
close(mapper_pipes[3][PIPE_WRITE_END]);
close(mapper_pipes[3][PIPE_READ_END]);
break;
default :
printf("you did something wrong in send_lines_to_mappers loop");
}
count++;
}
fclose(input_file);
}
int main(void) {
init_letter_count();
// Setup the mapper pipes
create_mapper_pipes();
create_reducer_pipes();
fork_reducers();
fork_mappers();
send_lines_to_mappers();
return 0;
}
When you create a pipe, there are two ends ("file descriptors"), the reading end and the writing end.
When you fork(), the child process inherits ALL the open file descriptors, including both ends of ANY open pipe.
So, if you want:
[child1] >===pipe1===> [parent] >===pipe2===> [child2]
for example, then you have a several file descriptors to close.
In child1, you need to close the READ end of pipe1 AND BOTH ends of
pipe2.
In child2, you need to close the WRITE end of pipe2 and BOTH ends of
pipe1.
In the parent, after you are done forking, you need to close the
WRITE end of pipe1 and the READ end of pipe2.
As you have lots of pipes, you will have even more closing to do.
If you are not sure you have everything closed, the program lsof ("list open file-descriptors") can be helpful.
For educational purposes, I wrote a program that forks a process and ...
the child continuously reads 3 files, prints the contents, sleeps for 10ms.
the parent keeps a counter for each file. each file also has a delay time associated with it.
each time a file's timer expires, the counter is incremented and the file is overwritten with the
new counter value. Each delay value is different, so all 3 files get updated at different rates.
The problem is, the counters only increment for a short time, and everything freezes after a few seconds. Can anyone give a good explanation of what is happening here?
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/time.h>
#define CHAN1WAIT 100000
#define CHAN2WAIT 750000
#define CHAN3WAIT 1000000
#define NCHAN 3
FILE *chanfiles[NCHAN] = {NULL, NULL, NULL}; //file pointers for fake 'devices'
char *filenames[NCHAN] = {"_chan1tmpfile_", "_chan2tmpfile_", "_chan3tmpfile_"};
int chanwait[NCHAN] = {CHAN1WAIT, CHAN2WAIT, CHAN3WAIT}; //time it takes for each 'device' to be updated with a new value
int chancount[NCHAN] = {0, 0, 0}; //value for each device
int clrcount = NCHAN * 8;
uint8_t chan1;
int read_chan (int chan)
{
char buf[4];
char c;
int i, ret;
short count = 0;
uint8_t set = 0;
char * retstr;
while (! set)
{
if (chanfiles[chan] == NULL) //if file is not in use
{
if ((chanfiles[chan] = fopen(filenames[chan], "r")) == NULL)
{
printf("Error opening file %s for reading.\n%s\n", filenames[chan], strerror(errno));
exit(-1);
}
while ((c = fgetc(chanfiles[chan])) != EOF)
{
buf[count] = c;
count++;
}
fclose(chanfiles[chan]);
chanfiles[chan] = NULL;
retstr = malloc(count + 1);
for (i = 0; i < count; i++) retstr[i] = buf[i];
ret = atoi(retstr);
free(retstr);
set = 1;
}
}
return ret;
}
void write_chan (int chan)
{
uint8_t set = 0;
while (! set)
{
if (chanfiles[chan] == NULL) //if file is not in use
{
if ((chanfiles[chan] = fopen(filenames[chan], "w")) == 0)
{
printf("Error opening file %s for writing.\n%s\n", filenames[chan], strerror(errno));
exit(-1);
}
if (fprintf(chanfiles[chan], "%d", chancount[chan]) < 0)
{
printf("Error writing to file %s:\n%s\n", filenames[chan], strerror(errno));
exit(-1);
}
fclose(chanfiles[chan]);
chanfiles[chan] = NULL;
set = 1;
}
}
}
time_t get_usecs()
{
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec + tv.tv_usec;
}
int main (int argc, char * argv[])
{
pid_t pid;
time_t curtime;
int i;
for (i = 0; i < NCHAN; i++) write_chan(i);
printf("\nChannel:");
for (i = 0; i < NCHAN; i++) printf("%8d", i);
printf("\n Value:");
pid = fork();
// This process reads all 3 files, prints the values,
// then sleeps for 10ms, in an infinite loop.
if (pid == 0)
{
int j;
while (1)
{
uint8_t set;
for (j = 0; j < NCHAN; j++)
{
int value;
set = 0;
value = read_chan(j);
printf("%8d", value);
}
fflush(stdout);
usleep(10000);
for (j = 0; j < clrcount; j++) printf("\b"); fflush(stdout);
}
}
// This process updates the values of all 3 files at
// different rates, based on the value in chanwait[]
// for each file.
else
{
time_t timers[NCHAN];
int i;
for (i = 0; i < NCHAN; i++) timers[i] = get_usecs();
while (1)
{
for (i = 0; i < NCHAN; i++)
{
if ((get_usecs() - timers[i]) >= chanwait[i])
{
chancount[i]++;
write_chan(i);
timers[i] = get_usecs();
}
}
}
}
}
I am not sure this is your only problem, but your get_usecs function is suspect. You probably meant this
return tv.tv_sec * 1000000 + tv.tv_usec;
Rather than
return tv.tv_sec + tv.tv_usec;
Although, note that time_t is only guaranteed to be large enough for the time in seconds, not the number of microseconds as you have used it.
The task was to create simulation of warehouse's work. Producers (in an amount of argv[2]) create random number of "goods" (totally argv[1]), and consumers (in an amount of argv[3]) get random number of these goods. The full code is below.
I got segmentation error and tried to debug it and got the following:
Program received signal SIGSEGV, Segmentation fault.
__new_sem_init (sem=0x37, pshared=0, value=1) at sem_init.c:44
44 sem_init.c: No such file or directory
I think the problem is in address-of operator here
sem_init(&(shared->mutex), 0, 1);
How should I change the code to make it work?
Thanks a lot!
#include <unistd.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/mman.h>
#define NBUFF 10
#define MAXNTHREADS 100
#define min( a, b ) ( ( a < b) ? a : b )
int nitems, nproducers, nconsumers;
typedef struct shared_s
{
int buff[NBUFF];
int nput;
int nputval;
int nget;
int ngetval;
sem_t mutex, nempty, nstored;
} sharedtype;
int main(int argc, char **argv)
{
sharedtype * shared;
key_t key;
int shmid, semid;
int i, j, prodcount[MAXNTHREADS], conscount[MAXNTHREADS];
shared = mmap(NULL, sizeof(sharedtype),
PROT_READ | PROT_WRITE, MAP_SHARED, -1, 0);
/* Wrong argv */
if (argc != 4)
{
printf("usage: newconsumer <#items> <#producers> <#consumers>\n");
exit(1);
}
nitems = atoi(argv[1]);
nproducers = min(atoi(argv[2]), MAXNTHREADS);
nconsumers = min(atoi(argv[3]), MAXNTHREADS);
pid_t chpidpr [nproducers];
pid_t chpidcon [nconsumers];
/* initilising semaphores */
sem_init(&(shared->mutex), 0, 1);
sem_init(&(shared->nempty), 0, NBUFF);
sem_init(&(shared->nstored), 0, 0);
for (i = 0; i < nproducers; i++) {
prodcount[i] = 0;
switch (chpidpr[i] = fork())
{
case -1:
printf("fork error");
return 1;
case 0:
for (;;)
{
sem_wait(&shared->nempty);
sem_wait(&shared->mutex);
if (shared->nput >= nitems)
{
sem_post(&(shared->nstored));
sem_post(&(shared->nempty));
sem_post(&(shared->mutex));
return 0;
}
shared->buff[(shared->nput) %NBUFF] = shared->nputval;
(shared->nput)++;
(shared->nputval)++;
sem_post(&(shared->mutex));
sem_post(&(shared->nstored));
prodcount[i] += 1;
}
}
}
for (i = 0; i < nproducers; i++)
{
printf("producer count[%d] = %d\n", i, prodcount[i]);
}
for (i = 0; i < nconsumers; i++) {
conscount[i] = 0;
switch (chpidcon[i] = fork())
{
case -1:
printf("error");
return 1;
case 0:
for (;;)
{
sem_wait(&(shared->nstored));
sem_wait(&(shared->mutex));
if (shared->nget >= nitems)
{
sem_post(&(shared->nstored));
sem_post(&(shared->mutex));
return 0;
}
j = shared->nget % NBUFF;
if (shared->buff[j] != shared->ngetval)
{
printf("error: buff[%d] = %d\n", j, shared->buff[j]);
}
shared->nget++;
shared->ngetval++;
sem_post(&(shared->mutex));
sem_post(&(shared->nempty));
conscount[i] += 1;
}
}
}
for (i = 0; i < nconsumers; i++)
{
printf("consumer count[%d] = %d\n", i, conscount[i]);
}
/* destroying semaphores */
sem_destroy(&(shared->mutex));
sem_destroy(&(shared->nempty));
sem_destroy(&(shared->nstored));
exit(0);
}
It looks like your mmap call has failed and return -1. You aren't checking for this condition.
I did a quick addition, and it looks like mutex is at an offset of 56, or 0x38 from the base of sharedtype. Based on the crash report, sem = 0x37, which would be the address of shared->mutex if shared == -1.
I can't find any documentation on why one would call mmap with fd == -1, but I think this may be the source of the issue, combined with not validating the result.
I'm trying to get 2 way communication between a main file and a helper file.
The main file forks, and the child does some pipe work and then runs an exec.
My problem is that I can send information from the child exec to the parent exec, but not the other way around.
Below Is my entire code from the two files, so you should be able to run it.
Any help in getting the 2 way communication working will be extremely helpful. i'm been at this for almost 8 hours straight now.
When you run it, you'll see it print out "yo 0". This was me testing that it takes an integer from the main file, sends it to the helper, adds yo in front of it and sends it back. The first slab of code is the main file, second is the helper, third is the map file needed to run it. make sure there isn't a blank line underneath the last line, and the fourth is the agent file needed to run it.
the running is [./handler mapfile 20 agentfile.]
the int 20 doesn't do anything yet, but you need it in there to run the file.
If anyone actually goes to the effort to do all this and help me, i am eternally grateful
main file (handler.c)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/wait.h>
enum ErrorCode {
SHOW_USAGE = 1, BAD_STEPS, OPEN_MAP_ERROR, CORRUPT_MAP,
OPEN_AGENT_ERROR, CORRUPT_AGENTS, AGENT_ERROR,
AGENT_WALLED, AGENT_COLLIDED, TOO_MANY_STEPS, INVALID_AGENT_RESPONSE,
AGENT_CLOSED, AGENT_DIED, SIGINT_REC
};
typedef struct {
int valid;
int row, col;
} Point;
typedef struct {
Point point;
int number;
char name;
char param[20];
char type[20];
} Agent;
typedef struct {
int rows, cols;
char **grid;
} Map;
Map map;
Map agentMap;
int listSize = 0;
void error(enum ErrorCode e) {
switch(e) {
case SHOW_USAGE:
fprintf(stderr, "Usage: handler mapfile maxsteps agentfile\n");
break;
case BAD_STEPS:
fprintf(stderr, "Invalid maxsteps.\n");
break;
case OPEN_MAP_ERROR:
fprintf(stderr, "Unable to open map file.\n");
break;
case CORRUPT_MAP:
fprintf(stderr, "Corrupt map.\n");
break;
case OPEN_AGENT_ERROR:
fprintf(stderr, "Unable to open agent file.\n");
break;
case CORRUPT_AGENTS:
fprintf(stderr, "Corrupt agents.\n");
break;
case AGENT_ERROR:
fprintf(stderr, "Error running agent.\n");
break;
case AGENT_WALLED:
fprintf(stderr, "Agent walled.\n"); // needs fixing, check spec sheet
break;
case AGENT_COLLIDED:
fprintf(stderr, "Agent collided.\n"); // same as AGENT_WALLED
break;
case TOO_MANY_STEPS:
fprintf(stderr, "Too many steps.\n");
break;
case INVALID_AGENT_RESPONSE:
fprintf(stderr, "Agent sent invalid response.\n"); // fixiing
break;
case AGENT_CLOSED:
fprintf(stderr, "Agent exited with status.\n"); // fixiing
break;
case AGENT_DIED:
fprintf(stderr, "Agent exited due to signal.\n"); // fixing
break;
case SIGINT_REC:
fprintf(stderr, "Exiting due to INT signal.\n");
break;
}
exit(e);
}
void print_map(Map map)
{
int r;
for (r = 0; r < map.rows; ++r) {
printf("%s", map.grid[r]);
}
puts("");
}
void print_agents(Agent *agents, int size)
{
int i;
for (i = 0; i < size; i++) {
Agent temp = agents[i];
printf("%d %d %c %d %s %s %i\n", temp.point.row, temp.point.col, temp.name, temp.number, temp.type, temp.param, i);
}
puts("");
}
void readMap(char *file)
{
int r;
FILE *fd = fopen(file, "r");
char buffer[20];
char d;
if (!fd) {
error(OPEN_MAP_ERROR);
}
if (fgets(buffer, 20, fd) == NULL) {
error(CORRUPT_MAP);
}
if (sscanf(buffer, "%d %d%1[^\n]\n", &map.rows, &map.cols, &d) != 2 ||
map.rows < 1 || map.rows > 999 || map.cols < 1 || map.cols > 999) {
error(CORRUPT_MAP);
}
map.grid = malloc(map.rows * sizeof(char *));
for (r = 0; r < map.rows; ++r) {
map.grid[r] = calloc(map.cols + 2, sizeof(char));
if (fgets(map.grid[r], map.cols + 2, fd) == NULL ||
map.grid[r][map.cols] != '\n') {
error(CORRUPT_MAP);
}
}
fclose(fd);
}
void checkAgent(char *file)
{
FILE *fd = fopen(file, "r");
if (!fd) {
error(AGENT_ERROR);
}
fclose(fd);
}
int growList (Agent **agentList, int curSize, int increaseNum)
{
const int newSize = curSize + increaseNum;
Agent *temp = (Agent*) realloc(*agentList, (newSize * sizeof(Agent)));
if (temp == NULL) {
exit(20);
}
else {
*agentList = temp;
return newSize;
}
}
Agent* readAgentFile(char *file, Agent *agentList)
{
int readCount = 0;
FILE *fp = fopen(file, "r");
char buffer[80];
listSize = 0;
if (!fp) {
error(OPEN_AGENT_ERROR);
}
if (fgets(buffer, 80, fp) == NULL) {
error(CORRUPT_AGENTS);
}
rewind(fp);
while (fgets(buffer, 80, fp) != NULL) {
if (buffer[0] != '#') {
Agent agent;
sscanf( buffer, "%d %d %c %s %s" ,&agent.point.row, &agent.point.col, &agent.name, agent.type, agent.param);
checkAgent(agent.type);
agent.number = readCount+1;
listSize = growList(&agentList, listSize, 1);
agentList[readCount] = agent;
readCount++;
}
}
if (readCount == 0) {
error(CORRUPT_AGENTS);
}
fclose(fp);
return agentList;
}
void createAgentMap()
{
int i,j;
agentMap = map;
for (i=0; i < map.rows; i++) {
for (j=0; j < map.cols; j++) {
char c = map.grid[i][j];
if (c == '.') {
agentMap.grid[i][j] = ' ';
}
}
}
}
int main(int argc, char **argv)
{
int steps;
int pid;
int returnStatus;
int i;
int out_pipe[2];
int in_pipe[2];
char ch[20];
Agent firstAgent;
Agent *agentList =(Agent *) calloc(1, sizeof(Agent));
if (argc != 4) {
error(SHOW_USAGE);
}
sscanf(argv[2], "%d", &steps);
if ((steps < 1)) {
error(BAD_STEPS);
}
readMap(argv[1]);
agentList = readAgentFile(argv[3], agentList);
firstAgent = agentList[0];
createAgentMap();
for (i=0; i < listSize; i++) {
if (pipe(out_pipe) < 0) {
perror("Pipe Error");
}
if (pipe(in_pipe) < 0) {
perror("Child pipe error");
}
Agent temp;
temp = agentList[i];
switch ( pid = fork() )
{
case -1:
perror("Can't fork.\n");
exit(20);
case 0:
/* Child */
/*close(1);
dup(in_pipe[1]);
close(0);
dup(out_pipe[0]);
close(in_pipe[0]);
close(out_pipe[1]);*/
dup2(out_pipe[0], 0);
dup2(in_pipe[1], 1);
execlp(temp.type, temp.type, temp.param, (char *)0);
perror("No exec");
default:
//close(1);
//dup(handlerChild[1]);
//fprintf(stdout, "%d", listSize);
write(out_pipe[1], "%d", listSize);
close(in_pipe[1]);
close(0);
dup(in_pipe[0]);
if (fgets(ch, 20, stdin) == NULL) {
break;
}
printf("%s\n", ch);
}
}
while (steps > 0) {
steps -= 1;
}
return 0;
}
helper file (simple.c)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
typedef struct {
int valid;
int row, col;
} Point;
typedef struct {
int numAgents;
char agentNames[80];
int agentNumber;
} Info;
typedef struct {
int rows, cols;
char **grid;
} Map;
Map agent_map;
int main(int argc, char **argv)
{
int steps = 10;
int simple_pipe[2];
int dir;
char inputDir;
char input_stream[20];
int in = dup(0);
Info info;
if (argc == 2) {
sscanf(argv[1], "%c1", &inputDir);
switch (inputDir) {
case 'N': dir = 0; break;
case 'E': dir = 1; break;
case 'S': dir = 2; break;
case 'W': dir = 3; break;
default : fprintf(stdout, "Invalid params.\n"); exit(2);
}
}
else {
fprintf(stdout, "Incorrect number of params.\n");
exit(1);
}
close(0);
dup(simple_pipe[0]);
fgets(input_stream, 20, stdin);
sscanf(input_stream, "%d", &info.numAgents);
//printf("%d", info.numAgents);
//printf("this is the input: %s\n", input_stream); // This is successfully printing to stdout in the pipe
fprintf(stderr, "yo %d \n", info.numAgents);
while (steps > 0) {
steps -= 1;
}
exit(0);
}
map file
6 6
##..##
#....#
#.##.#
#....#
##....
######
agent file
1 1 A ./simple E
2 2 B ./simple N
5 2 C ./simple S
A pipe is a unidrectional connection across processes. Before you fork, you open the pipe and it will reserve two file descriptors, where fd[0] can be read from and fd[1] can be written to.
So when you want to have a two way commumincation you need to create two pipes, and then use one for reading in the parent writing in the child and the second pipe the other way around.
A more detailed explanation along with some sample code can be foun dhere: http://linux.die.net/man/2/pipe