Below is my PID manager. I want to modify it so it uses multi-threading. Therefore I would like for each thread to request a pid (maybe create 20 or so like I do in the while loop), sleep for a random period of time (I assume use sleep() ), and then release the pid (similar to what you see below).
I am a total newbie when it comes to threads in C and Linux so if someone can help me modify this accordingly. Would I start with the clone() function call?
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#define MIN_PID 300
#define MAX_PID 5000
#define CB CHAR_BIT
int sz = MAX_PID - MIN_PID + 1;
unsigned char *unsignedChar;
int allocate_map();
int allocate_pid();
void release_pid(int pid);
int main()
{
int map = allocate_map();
if (map == 1) {
printf("
Bitmap Data Structure initialized.
");
int id = 0, i = 0;
//create 20 processes
while (i < 20) {
int val = allocate_pid();
printf("
Process %d: pid = %d", i+1, val);
i++;
}
//release a few processes
release_pid(303); printf("
Process 303 released.");
release_pid(308); printf("
Process 308 released.");
release_pid(309); printf("
Process 309 released.");
//allocate a few more processes after this release
int val = allocate_pid(); printf("
Process %d : pid = %d", ++i, val); //should be 303
val = allocate_pid(); printf("
Process %d : pid = %d
", ++i, val); //should be 308
}
else printf("
Failed to initialize data structure.
");
}
/* Creates and initializes a bitmap data structure for representing pids;
returns —1 for unsuccessful, 1 for successful */
int allocate_map() {
unsignedChar = (unsigned char*)malloc((sz+CB-1)/CB * sizeof(char));
if (unsignedChar) return 1;
return -1;
}
/* Allocates and returns a pid; returns -1
if it is unable to allocate a pid (all pids are in use) */
int allocate_pid() {
int i = 0;
int pid = unsignedChar[i/CB] & (1 << (i & (CB-1)));
while (pid != 0) {
i++;
pid = unsignedChar[i/CB] & (1 << (i & (CB-1)));
}
if (i+MIN_PID > MAX_PID) return -1;
unsignedChar[i/CB] |= 1 << (i & (CB-1));
return i+MIN_PID;
}
/* Releases a pid given a pid parameter*/
void release_pid(int pid) {
if (pid < 300) {
printf("
Invalid PID: It should lie between 300 and 3000.");
return;
}
int i = pid - MIN_PID;
unsignedChar[i/CB] &= ~(1 << (i & (CB-1)));
}
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