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Add process fork (albeit non-functioning)

This commit is contained in:
Ivaylo Ivanov 2018-12-14 19:51:54 +01:00
parent 563cced7ea
commit 446ac678db
1 changed files with 158 additions and 25 deletions
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183
cpair/cpair.c
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@ -26,7 +26,9 @@
* The program does the following:
* - No output if the array has one point
* - The points if the array has 2 points
* - Otherwise, the array is split in 2 parts based on the mean of X and sent to 2 different paralell child processes. The parent watches for the return code of the children and terminates with an error if any of the children exit with anything other than success.
* - Otherwise, the array is split in 2 parts based on the mean of X and sent to 2 different paralell child processes.
* The parent watches for the return code of the children and terminates with an error if any of the children exit
* with anything other than success.
*
* Algorithm description when there are more than 2 points:
* - P1 and P2 are the closest pairs for the first and the second part respectively.
@ -44,18 +46,24 @@
/// Node struct for linked list
typedef struct node {
/**
* points[0] - contains the X coordinate of the point
* points[1] - contains the Y coordinate of the point
*
**/
float points[2];
struct node * next;
} node_t;
float get_x_mean(node_t * head);
float get_distance(float x1, float x2, float y1, float y2);
node_t * find_shortest_distance(node_t * list);
int wait_for_termination(pid_t child);
int main(void) {
char input[__UINT8_MAX__] = ""; ///< An array to save the input to
int point_num = 0; ///< Save the number of points
node_t * head = NULL;
pid_t child_a, child_b;
head = malloc(sizeof(node_t));
@ -74,13 +82,13 @@ int main(void) {
current = current -> next;
point_num++; ///< Increase the list length
} else {
puts("ERROR: Ill-formed line found");
fprintf(stderr, "ERROR: Ill-formed line found\n");
exit(EXIT_FAILURE);
}
}
if(feof(stdin) == 0) {
puts("ERROR: An error interrupted the read");
fprintf(stderr, "ERROR: An error interrupted the read\n");
exit(EXIT_FAILURE);
}
@ -95,35 +103,98 @@ int main(void) {
float x_mean = get_x_mean(head);
child_a = fork();
child_b = fork();
node_t * first_part = malloc(sizeof(node_t));
node_t * second_part = malloc(sizeof(node_t));
switch(child_a){
node_t * first_part_buff = first_part;
node_t * second_part_buff = second_part;
/// Separate the lists based on the mean
current = head;
while(current != NULL) {
if(current -> points[0] <= x_mean) {
first_part_buff -> points[0] = current -> points[0];
first_part_buff -> next = malloc(sizeof(node_t));
first_part_buff = first_part_buff -> next;
} else {
second_part_buff -> points[0] = current -> points[0];
second_part_buff -> next = malloc(sizeof(node_t));
second_part_buff = second_part_buff -> next;
}
current = current -> next;
}
/**
* Create the pipe file descriptors and inititalize the pipes
*
* fd[0] - input side of pipe
* fd[1] - output side of pipe
*
**/
int pipe_a[2], pipe_b[2];
if(pipe(pipe_a) < 0 || pipe(pipe_b) < 0) {
fprintf(stderr, "ERROR: Failed creating the pipe\n");
exit(EXIT_FAILURE);
}
pid_t child_a, child_b; ///< Create variables for the child processes
node_t * child_a_part = NULL;
node_t * child_b_part = NULL;
write(pipe_a[0], first_part, sizeof(node_t)); ///< Send the first part of the array to the child
switch(child_a = fork()) {
case -1:
puts("ERROR: Coudn't fork child");
fprintf(stderr ,"ERROR: Couldn't fork child\n");
exit(EXIT_FAILURE);
case 0:
puts("Child");
if(read(pipe_a[0], child_a_part, sizeof(node_t)) < 0) {
fprintf(stderr, "ERROR: Failed reading from pipe\n");
exit(EXIT_FAILURE);
}
if(write(pipe_a[1], find_shortest_distance(child_a_part), sizeof(node_t)) < 0) {
fprintf(stderr, "ERROR: Failed writing to pipe\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
break;
default:
write(pipe_b[0], second_part, sizeof(node_t));
switch(child_b = fork()) {
case -1:
fprintf(stderr, "ERROR: Couldn't fork child\n");
exit(EXIT_FAILURE);
case 0:
if(read(pipe_b[0], child_b_part, sizeof(node_t)) < 0) {
fprintf(stderr, "ERROR: Failed reading from pipe\n");
exit(EXIT_FAILURE);
}
if(write(pipe_b[1], find_shortest_distance(child_b_part), sizeof(node_t)) < 0) {
fprintf(stderr, "ERROR: Failed writing to pipe\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
break;
default:
break;
}
break;
}
switch(child_b){
case -1:
puts("ERROR: Coudn't fork child");
exit(EXIT_FAILURE);
case 0:
puts("Child");
break;
default:
break;
}
if(wait_for_termination(child_a) != EXIT_SUCCESS)
exit(EXIT_FAILURE);
int status;
if(wait_for_termination(child_b) != EXIT_SUCCESS)
exit(EXIT_FAILURE);
waitpid(child_a, &status, 0);
waitpid(child_b, &status, 0);
/// Free the memory
free(head);
free(first_part);
free(first_part_buff);
free(second_part);
free(second_part_buff);
free(current);
exit(EXIT_SUCCESS);
}
@ -138,14 +209,15 @@ int main(void) {
float get_x_mean(node_t * head) {
node_t * current = head;
float x_sum = 0;
int i = 0;
while(current -> next != NULL) {
int i = 1;
while(current != NULL) {
x_sum += current -> points[0];
current = current -> next;
i++;
}
return x_sum/i;
return x_sum/(i - 2); ///< TODO: Fix the bug with the 2 more iterations
}
/**
@ -160,3 +232,64 @@ float get_x_mean(node_t * head) {
float get_distance(float x1, float x2, float y1, float y2) {
return sqrt(pow((x2 - x1), 2) + pow((y2 - y1), 2));
}
/**
* @brief Function to find the shortest distance in a list
* @details The function gets a list of points and finds the pair
* with the shortest distance between them.
* @param list - the list with points
* @return res - a list containing the coordinates of the two closest points
*
**/
node_t * find_shortest_distance(node_t * list) {
node_t * current = list;
node_t * next = list;
/// Setup the result list
node_t * res = malloc(sizeof(node_t));
res -> next = malloc(sizeof(node_t));
int current_shortest = 0;
int new_shortest = 0;
while(current != NULL) {
next = current -> next;
if(next != NULL) {
new_shortest = get_distance(current -> points[0], next -> points[0], current -> points[1], next -> points[1]);
if(new_shortest < current_shortest) {
current_shortest = new_shortest;
/// Save the pairs
res -> points[0] = current -> points[0];
res -> points[1] = current -> points[1];
res -> next -> points[0] = next -> points[0];
res -> next -> points[1] = next -> points[1];
}
current = next;
} else
break;
}
return res;
}
/**
* @briefs Function that waits for a child to close
* @details The function waits for a child to close.
* If it closes successfully, it returns the exit status only.
* Otherwise, it prints an error message and then returns the exit status.
* @param child - the pid of the child process
* @return the exist status of the child process
*
**/
int wait_for_termination(pid_t child) {
int exit_stat = 0;
if(waitpid(child, &exit_stat, 0) < 0) {
fprintf(stderr, "ERROR: Child did not exit successfully\n");
}
return WEXITSTATUS(exit_stat);
}