Implementing first fit like algorithm - c

Question

Problem:
I have 3 machines, each machine have a limit of 30 ms time, each machine have 3 zones that a task can't be executed there.
The tasks have a P (priority) and W (weight, which is the time to complete the task in this setup), tasks must be first ordered by a priority, from lower to higher like this:
Task 01 {6, 2} // P/W = 3 this task executed last (3)
Task 02 {7, 7} // P/W = 1 this task executed first (1)
Task 03 {4, 2} // P/W = 2 this task executed second (2)
Now, in order to execute a tasks(I have 6), I must check all 3 machines to find the first fit to the task, to chose a fit for task, it must be the optimal in the 3 machines, example:
Machine 01; |-----5----9-------16-17--19-20|
Machine 02: |----4-5--7-8---------17-18--|
Machine 03: |-----5---8--10---13--15---18--|
(1)Task 02 executed in machine 02 (We look for P ms to execute task, and the minimum time to start a task, since both machine 01 (starting from 9 ms) and 02 (starting from 8 ms) have a 7 ms free time, machine 02 can start a task first then the machine 01).
(2)Task 03 executed in machine 02 (We look for P ms to execute task).
(3)Task 01 executed in machine 01 (We look for P ms to execute task).
Certain periods of time are defined as critical, and cannot be used to schedule a job. These periods (for instance 5-9, 7-8), are stored in the dedicated struct z_indispo.
The bfeet struct is used to store in witch the task start and in witch machine.
I implemented mostly the entire algorithm in C, but my results are different than expected:
#include <stdio.h>
typedef struct _z_indispo {
int t1;
int t2;
} z_indispo;
typedef struct _machines {
int t[20]; // array represent time
z_indispo zone[2];
} machines;
typedef struct _tache {
int p;
int w;
int c; // p/w
int i; // Task number
} tache;
typedef struct _bfeet {
int t; // Store the time to of ending execution by a task
int m; // The machine responsible for executing a task.
} bfeet;
int main(int argc, char **argv)
{
machines m[4];
tache j[6];
tache j_tmp;
bfeet b[4];
int i = 0;
int n = 0;
int u = 0;
int k = 0;
int count = 0;
int trouver = 0;
int f_totale = 0;
int f[3] = {0};
m[0].zone[0].t1 = 7;
m[0].zone[0].t2 = 9;
m[0].zone[1].t1 = 14;
m[0].zone[1].t2 = 15;
m[1].zone[0].t1 = 8;
m[1].zone[0].t2 = 9;
m[1].zone[1].t1 = 16;
m[1].zone[1].t2 = 17;
m[2].zone[0].t1 = 7;
m[2].zone[0].t2 = 8;
m[2].zone[1].t1 = 18;
m[2].zone[1].t2 = 19;
/*
* Initialise all machines
* 0: Represent free time.
* -1: Represent critical zone range.
* -2: Represent a task already executed.
*/
for(i = 0; i< 3; ++i)
{
for(count = 0; count < 20; ++count)
{
if((count >= m[i].zone[0].t1 - 1 && count <= m[i].zone[0].t2 - 1) ||
(count >= m[i].zone[1].t1 - 1 && count <= m[i].zone[1].t2 - 1))
{
m[i].t[count] = -1;
}
else
{
m[i].t[count] = 0;
}
}
}
for(i = 0; i< 3; ++i)
{
if(i == 0)
printf(" D(1,1) t1 s1 D(1,2) t2 s2 D(1,3)\n");
else if(i == 1)
printf(" D(2,1) t1 s1 D(2,2) t2 s2 D(2,3)\n");
else if(i == 2)
printf(" D(3,1) t1 s1 D(3,2) t2 s2 D(3,3)\n");
printf("|");
for(count = 0; count < 20; ++count)
{
printf("%3d", m[i].t[count]);
}
printf(" |\n\n");
}
j[0].p = 5;
j[0].w = 2;
j[0].i = 1;
j[1].p = 9;
j[1].w = 3;
j[1].i = 2;
j[2].p = 6;
j[2].w = 3;
j[2].i = 3;
j[3].p = 6;
j[3].w = 4;
j[3].i = 4;
j[4].p = 7;
j[4].w = 7;
j[4].i = 5;
/*
* Calc C = P/W .
*/
for(count = 0; count < 5; ++count)
{
j[count].c = j[count].p / j[count].w;
}
/*
* Sort tasks from low to hight
*/
for(count = 0; count < 5; ++count)
{
for(k = 0; k < 5 - count; ++k)
{
if(j[k].c > j[k + 1].c)
{
j_tmp = j[k + 1];
j[k + 1] = j[k];
j[k] = j_tmp;
}
}
}
/*printf("|%2J |%2 P |%2 W | C |\n");
printf("_____________________\n");
for(count = 0; count < 5; ++count)
{
printf("|%-4d|%-4d|%-4d|%-4d|\n", j[count].i, j[count].p, j[count].w, j[count].c);
}
printf("\n");*/
/*
* Execute tasks
*/
while(n < 5)
{
for(count = 0; count < 3; ++count)
{
i = 0;
trouver = 0;
while(i <= 20 && trouver != 1)
{
if(m[count].t[i] == 0) // We have a free time to start with it.
{
u = 0; // num of available indexs.
while(m[count].t[i] != -1 && m[count].t[i] != -2)
{
if(u == j[n].p)
break;
++u;
++i;
}
if(u < j[n].p)
{
while(m[count].t[i] == -1 && m[count].t[i] == -2) // bypass unfree unites
++i;
}
else if(u == j[n].p)
{
b[count].t = i - u;
b[count].m = count; //
trouver = 1; // we find the Necessary unites to start a task
}
}
else
++i;
}
}
if(u < j[n].p)
printf("There is no free time to execute task %d", j[n].i);
else
{
// Find the minimum time in all machines to start a task
b[3].t = b[0].t;
b[3].m = b[0].m;
for(count = 0; count < 3; ++count)
{
if(b[3].t > b[count + 1].t)
{
b[3].t = b[count + 1].t;
b[3].m = b[count + 1].m;
}
}
// Put -2 to indicate that index is unfree
u = b[3].t + j[n].p;
for(count = b[3].t; count < u; ++count)
{
m[b[3].m].t[count] = -2;
}
if(b[3].m == 0)
f[0] = (b[3].t + j[n].p);
else if(b[3].m == 1)
f[1] = (b[3].t + j[n].p);
else if(b[3].m == 2)
f[2] = (b[3].t + j[n].p);
printf("Task %d end at %-2d, machine %d.\n", j[n].i, b[3].t + j[n].p, b[3].m + 1);
}
++n;
}
printf("\n");
f_totale = f[0] + f[1] + f[2];
printf("F of machine 01: %d.\n", f[0]);
printf("F of machine 02: %d.\n", f[1]);
printf("F of machine 03: %d.\n", f[2]);
printf("Total F: %d.\n", f_totale);
printf("\n");
/*printf("\n");
for(i = 0; i< 3; ++i)
{
if(i == 0)
printf(" D(1,1) t1 s1 D(1,2) t2 s2 D(1,3)\n");
else if(i == 1)
printf(" D(2,1) t1 s1 D(2,2) t2 s2 D(2,3)\n");
else if(i == 2)
printf(" D(3,1) t1 s1 D(3,2) t2 s2 D(3,3)\n");
printf("|");
for(count = 0; count < 20; ++count)
{
printf("%3d", m[i].t[count]);
}
printf(" |\n\n");
}*/
return 0;
}
UPDATE:
I have now only two unavailability zones in each machine. I also updated the code to fix some errors, but I still get a different output then this example:
I have this unavailability zones:
m[0].zone[0].t1 = 7;
m[0].zone[0].t2 = 9;
m[0].zone[1].t1 = 14;
m[0].zone[1].t2 = 15;
m[1].zone[0].t1 = 8;
m[1].zone[0].t2 = 9;
m[1].zone[1].t1 = 16;
m[1].zone[1].t2 = 17;
m[2].zone[0].t1 = 7;
m[2].zone[0].t2 = 8;
m[2].zone[1].t1 = 18;
m[2].zone[1].t2 = 19;
5 tasks:
p | 6 9 5 7 6
w | 3 3 2 7 4
_______________
c | 2 3 2 1 1
After ordering by c:
p | 7 6 5 6 9
w | 7 4 2 3 3
_______________
c | 1 1 2 2 3
The execution of tasks should be like this:
J4
|_______7__9_____14_15__________| ms
Task 04 should end at 7, P represent the time necessary to execute a task.
J5
|________8_9__________16_17_____| ms
Task 05 should end at 7.
J1 J3
|_______7_8_______________18_19_| ms
Task 01 should end at 6, task 03 should end at 14.
UPDATE 02: (This problem fixed)
I noticed a strange behavior in my program, after I initializing m[i].t[count] array, I found that variables responsible for storing unavailability zones changed:
NOTE: This problem fixed.
UPDATE03: (This problem fixed but with new issue)
I have situation when a task can't find the necessary unites to start, I never get this message "There is no free time to execute task ", witch I should receive it for task 2, since it has 9 unites, and all machines have no such of free time like that. The code responsible for this test:
for(count = 0; count < 3; ++count) // search on all machines
{
i = 0;
trouver = 0;
while(i < 20 && trouver != 1)
{
if(m[count].t[i] == 0) // We have a free time to start with it.
{
u = 0; // num of available indexs.
while(m[count].t[i] != -1 && m[count].t[i] != -2)
{
if(u == j[n].p)
break;
++u;
++i;
}
if(u < j[n].p)
{
while(m[count].t[i] == -1 && m[count].t[i] == -2) // bypass unfree unites
++i;
}
else if(u == j[n].p)
{
b[count].t = i - u;
b[count].m = count; //
trouver = 1; // we find the Necessary unites to start a task
}
}
else
++i;
}
}
/* u represent the number of continuous free time,
j[n].p represent the necessary time to execute the current task, n is the current task
if(u < j[n].p)
printf("There is no free time to execute task %d", j[n].i);
else
{
// Find the minimum time in all machines to start a task
b[3].t = b[0].t;
b[3].m = b[0].m;
UPDATE04:
Now I can see excluded task when there is no free time to execute a task, however, the output is not right, because I see a task override the period time on another task:
while(n < 5)
{
k = 0;
for(count = 0; count < 3; ++count)
{
i = 0;
u = 0;
trouver = 0;
while(i < 20 && trouver != 1)
{
if(m[count].t[i] == 0) // We have a free time to start with it.
{
//u = 0; // num of available indexs.
if(u == j[n].p)
break;
else
{
++u;
++i;
}
}
if(u != j[n].p)
{
if((m[count].t[i] == -1 || m[count].t[i] == -2))// bypass unfree unites
{
u = 0;
++i;
}
}
if(u == j[n].p)
{
++k;
b[count].t = i - u;
b[count].m = count; //
trouver = 1; // we find the Necessary unites to start a task
}
}
}
if(u != j[n].p)
{
printf("There is no free time to execute task %d.\n", j[n].i);
}
else
{
// Find the minimum time in all machines to start a task
b[3] = b[0];
for(count = 0; count < 3; ++count)
{
if(b[count].t != 0)
if(b[3].t > b[count + 1].t)
{
b[3] = b[count + 1];
}
}
// Put -2 to indicate that index is unfree
u = b[3].t + j[n].p;
for(count = b[3].t; count < u; ++count)
{
m[b[3].m].t[count] = -2;
}
if(b[3].m == 0)
f[0] = (b[3].t + j[n].p);
else if(b[3].m == 1)
f[1] = (b[3].t + j[n].p);
else if(b[3].m == 2)
f[2] = (b[3].t + j[n].p);
printf("Task %d end at %-2d, machine %d.\n", j[n].i, b[3].t + j[n].p, b[3].m + 1);
}
++n;
}
Output:
D(1,1) t1 s1 D(1,2) t2 s2 D(1,3)
| 0 0 0 0 0 0 -1 -1 -1 0 0 0 0 -1 -1 0 0 0 0 0 |
D(2,1) t1 s1 D(2,2) t2 s2 D(2,3)
| 0 0 0 0 0 0 0 -1 -1 0 0 0 0 0 0 -1 -1 0 0 0 |
D(3,1) t1 s1 D(3,2) t2 s2 D(3,3)
| 0 0 0 0 0 0 -1 -1 0 0 0 0 0 0 0 0 0 -1 -1 0 |
| J | P | W | C |
_____________________
|1 |5 |2 |2 |
|2 |7 |3 |2 |
|3 |8 |3 |2 |
|5 |17 |7 |2 |
|4 |16 |4 |4 |
Task 1 end at 5 , machine 1.
Task 2 end at 7 , machine 1.
Task 3 end at 8 , machine 1.
There is no free time to execute task 5.
There is no free time to execute task 4.
F of machine 01: 8.
F of machine 02: 0.
F of machine 03: 0.
Total F: 8.
D(1,1) t1 s1 D(1,2) t2 s2 D(1,3)
| -2 -2 -2 -2 -2 -2 -2 -2 -1 0 0 0 0 -1 -1 0 0 0 0 0 |
D(2,1) t1 s1 D(2,2) t2 s2 D(2,3)
| 0 0 0 0 0 0 0 -1 -1 0 0 0 0 0 0 -1 -1 0 0 0 |
D(3,1) t1 s1 D(3,2) t2 s2 D(3,3)
| 0 0 0 0 0 0 -1 -1 0 0 0 0 0 0 0 0 0 -1 -1 0 |

Answer 1

I found that the problem was in how I search for the minimum starting time in the machines to start task:
....
// Find the minimum time in all machines to start a task
b[3] = b[0]; // this cause the problem
for(count = 0; count < 3; ++count)
{
if(b[count].t != 0)
if(b[3].t > b[count + 1].t)
{
b[3] = b[count + 1];
}
}
b[3] as start could refer to a machine that can't start the current task, so I made a little change:
// Find the minimum time in all machines to start a task
for(count = 0; count < 3; ++count) // search only in the machines that can execute the current task
{
if(b[count].m != -1)
{
b[3] = b[count];
break;
}
}
for(count = 0; count < 3; ++count) // search for the first machines that can execute the current task
{
if(b[count].m != -1)
{
if((b[3].t > b[count + 1].t) && (b[count + 1].m != -1)) // make sure the next machine can start the current task
{
b[3] = b[count + 1];
}
}
}
The complete algorithm:
#include <stdio.h>
typedef struct _z_indispo {
int t1;
int t2;
} z_indispo;
typedef struct _machines {
int t[20]; // array represent time
z_indispo zone[2];
} machines;
typedef struct _tache {
int p;
int w;
int c; // p/w
int i; // Task number
} tache;
typedef struct _bfeet {
int t; // Store the time to of ending execution by a task
int m; // The machine responsible for executing a task.
} bfeet;
int main(int argc, char **argv)
{
machines m[4] = {0};
tache j[6];
tache j_tmp;
bfeet b[4] = {0};
int i = 0;
int n = 0;
int u = 0;
int k = 0;
int count = 0;
int trouver = 0;
int f_totale = 0;
int f[3] = {0};
m[0].zone[0].t1 = 7;
m[0].zone[0].t2 = 9;
m[0].zone[1].t1 = 14;
m[0].zone[1].t2 = 15;
m[1].zone[0].t1 = 8;
m[1].zone[0].t2 = 9;
m[1].zone[1].t1 = 16;
m[1].zone[1].t2 = 17;
m[2].zone[0].t1 = 7;
m[2].zone[0].t2 = 8;
m[2].zone[1].t1 = 18;
m[2].zone[1].t2 = 19;
/*
* Initialise all machines
* 0: Represent free time.
* -1: Represent critical zone range.
* -2: Represent a task already executed.
*/
for(i = 0; i< 3; ++i)
{
for(count = 0; count < 20; ++count)
{
if((count >= m[i].zone[0].t1 - 1 && count <= m[i].zone[0].t2 - 1) ||
(count >= m[i].zone[1].t1 - 1 && count <= m[i].zone[1].t2 - 1))
{
m[i].t[count] = -1;
}
else
{
m[i].t[count] = 0;
}
}
}
for(i = 0; i< 3; ++i)
{
if(i == 0)
printf(" D(1,1) t1 s1 D(1,2) t2 s2 D(1,3)\n");
else if(i == 1)
printf(" D(2,1) t1 s1 D(2,2) t2 s2 D(2,3)\n");
else if(i == 2)
printf(" D(3,1) t1 s1 D(3,2) t2 s2 D(3,3)\n");
printf("|");
for(count = 0; count < 20; ++count)
{
printf("%3d", m[i].t[count]);
}
printf(" |\n\n");
}
j[0].p = 5;
j[0].w = 2;
j[0].i = 1;
j[1].p = 7;
j[1].w = 3;
j[1].i = 2;
j[2].p = 4;
j[2].w = 1;
j[2].i = 3;
j[3].p = 6;
j[3].w = 4;
j[3].i = 4;
j[4].p = 7;
j[4].w = 7;
j[4].i = 5;
/*
* Calc C = P/W .
*/
for(count = 0; count < 5; ++count)
{
j[count].c = j[count].p / j[count].w;
}
/*
* Sort tasks from low to hight
*/
for(count = 0; count < 5; ++count)
{
for(k = 0; k < 5 - count; ++k)
{
if(j[k].c > j[k + 1].c)
{
j_tmp = j[k + 1];
j[k + 1] = j[k];
j[k] = j_tmp;
}
}
}
printf("|%2J |%2 P |%2 W | C |\n");
printf("_____________________\n");
for(count = 0; count < 5; ++count)
{
printf("|%-4d|%-4d|%-4d|%-4d|\n", j[count].i, j[count].p, j[count].w, j[count].c);
}
printf("\n");
/*
* Execute tasks
*/
while(n < 5)
{
k = 0;
for(count = 0; count < 3; ++count)
{
i = 0;
u = 0;
trouver = 0;
while(i < 20 && trouver != 1)
{
if(m[count].t[i] == 0) // we find a free unite
{
while(m[count].t[i] == 0 && u != j[n].p && i < 20) // count a continues free time, quit when u equal the necessary time to execute the current task
{
++u;
++i;
}
if(u == j[n].p) // we found a free continues time
{
b[count].t = i - u; // save the starting index
b[count].m = count; // save the machine responsible for executing the current task
++k;
trouver = 1;
}
else if(u != j[n].p) // if we encounter zone unavailability or index reserved by another task
{
u = 0; // restart u counter
while((m[count].t[i] == -1 || m[count].t[i] == -2) && (i < 20)) // bypass reserved/unavailability index's
++i;
}
}
else
++i; // bypass reserved/unavailability index's
}
if(trouver != 1) // we mark this machine as it can't execute the current task
{
b[count].m = -1;
}
}
if(k == 0)
printf("There is no free time to execute task %d.\n", j[n].i);
else
{
// Find the minimum time in all machines to start a task
for(count = 0; count < 3; ++count) // search only in the machines that can execute the current task
{
if(b[count].m != -1)
{
b[3] = b[count];
break;
}
}
for(count = 0; count < 3; ++count) // search only in the machines that can execute the current task
{
if(b[count].m != -1)
{
if((b[3].t > b[count + 1].t) && (b[count + 1].m != -1))
{
b[3] = b[count + 1];
}
}
}
// Put -2 to indicate that index as unfree
u = b[3].t + j[n].p;
for(count = b[3].t; count < u; ++count)
{
m[b[3].m].t[count] = -2;
}
if(b[3].m == 0)
f[0] = f[0] + (b[3].t + j[n].p) * j[n].w;
else if(b[3].m == 1)
f[1] = f[1] + (b[3].t + j[n].p) * j[n].w;
else if(b[3].m == 2)
f[2] = f[2] + (b[3].t + j[n].p) * j[n].w;
printf("Task %d end at %-3dms, machine %d.\n", j[n].i, b[3].t + j[n].p, b[3].m + 1);
}
++n;
}
printf("\n");
f_totale = f[0] + f[1] + f[2];
printf("F of machine 01: %d.\n", f[0]);
printf("F of machine 02: %d.\n", f[1]);
printf("F of machine 03: %d.\n", f[2]);
printf("Total F: %d.\n", f_totale);
printf("\n");
printf("\n");
for(i = 0; i< 3; ++i)
{
if(i == 0)
printf(" D(1,1) t1 s1 D(1,2) t2 s2 D(1,3)\n");
else if(i == 1)
printf(" D(2,1) t1 s1 D(2,2) t2 s2 D(2,3)\n");
else if(i == 2)
printf(" D(3,1) t1 s1 D(3,2) t2 s2 D(3,3)\n");
printf("|");
for(count = 0; count < 20; ++count)
{
printf("%3d", m[i].t[count]);
}
printf(" |\n\n");
}
return 0;
}

Answer 2

You have persistent short-by-one errors in your array definitions. Basically, C arrays are zero-indexed, so if you want to access array[n], array has to have been defined with size at least n+1. For instance your machine struct should be
typedef struct _machines {
int t[20];
z_indispo zone[2];
} machines;
since you access machine.t[20] and machine.zone[1].
This fixes the issue in your second update (memory getting stomped on like that is a pretty good indicator that you're indexing beyond the end of the array). The first one will likely get fixed (or at least you'll be a lot further along the road to a solution) once you fix the array initializations in main() similarly (e.g. you're accessing b[3].t, but since you defined it via bfeet b[3] it only has indices b[0], b[1] and b[2]).