taskVarAdd used twice for the same variable

Question

Hi All,

I have a global struct added to my task using taskVarAdd() API.

But during some scenarios, the same global struct is is added to the same task again using taskVarAdd() API. [i.e., taskVarAdd() is called twice from a task for a same variable].

This struct will maintain the taskID, message queue ids for that task.

My Questions:

1. If we call the taskVarAdd() for the same variable twice inside a task, what will be the behavior?
2. Whether the struct variable added first will be overwritten by the second variable?{I feel this will be overwritten]

Answer 1

The easiest way is to do a simple test case.

int v1;
void tvl()
{
   v1 = 1;
   taskVarAdd(0, &v1);
   v1 = 2;
   taskVarAdd(0, &v1);
   v1 = 3;
   taskDelay(1);
   printf("Initial v1 = %d\n", v1);
   for(;;)
   {
     v1++;
     taskDelay(60);
     printf("v1 = %d\n", v1);

   }
}

Running the test code results in the following values for v1:

Initial v1 = 2
1 3 3 2 4 4 3 5 5 4...

The same code with a single taskVarAdd gives the expected result of 1 2 3 4 ...

PS: You didn't specify the version of VxWorks, so what I said is valid for Vxworks 6.x

Answer 2

Hi Benoit,

Thanks For your response.

Currently we are using VxWorks 5.5

Kindly explain your program? Since i am new to VxWorks, i am not able to understnad the behavior clearly.

I have tested your code using tornado and i am getting different results every time i execute your program

//1st Attempt -> tv1 Inital v1 = V1 = 3 V1 = 3 V1 = 2 V1 = 4 V1 = 4 V1 = 3 V1 = 5 V1 = 5 V1 = 5 V1 = 6

//2nd attempt -> tv1 Inital v1 = V1 = 1 V1 = 3 V1 = 4 V1 = 2 V1 = 4 V1 = 5 V1 = 3 V1 = 5 V1 = 6

But When i commented the second taskVarAdd() and tested it, i am getting the consistent expected results as follows

//1st Attempt -> tv1 Inital v1 = 3 V1 = 4 V1 = 5 V1 = 6 V1 = 7 V1 = 8 V1 = 9 V1 = 10 V1 = 11 V1 = 12 V1 = 13

//2nd Attempt -> tv1 Inital v1 = 3 V1 = 4 V1 = 5 V1 = 6 V1 = 7 V1 = 8 V1 = 9 V1 = 10 V1 = 11 V1 = 12 V1 = 13

My Questions:

1. Is it right to use two taskVarAdd() inside same task for same variable?
2. Kindly explain the flow of your program