Thread: regarding anomalous execution of for loop and the function call

Hello,

Please excuse me as I have put this question on this forum before, but then I was away and did not follow with my post.

I have a for loop, and after this loop, I am calling another function that wakes a thread S, and then thread S carries on its execution.

Code:

        for (k = 0; k < num_msg; k++) { 
          if( (c % Messages[k][2] ) == 0 ) {
              printf("\n%d, act, %d\n", Messages[k][0], c );
          db_Lock();
          update_status( Messages[k][0], 1);
          db_UnLock();
         }
    }
    ret = invoke_thread_S();

I am getting an anomalous output. Before all the iterations of for loop could finish, the program enters into the invoke_thread_S() and I can see the remaining iterations of for loop happening after thread S is finished.

What could be the problem here. Can I put a 'sleep' before I enter into invoke_thread_S() function, I tried it with a very small amount (in nano seconds), but that did not solve the problem.

thanks,

Originally Posted by Salem

So if you write

Code:

printf("About to invoke thread\n");
ret = invoke_thread_S();

do you see all the output of the loop before the message "About to invoke thread"?

Let us say

Code:

 num_msg = 11

, and there is 2 values that fulfil the condition

Code:

 (c % Messages[k][2] ) == 0

, then in a particular run this is what happened:

Code:

1st_val, act, c
execution of thread S
2nd_val, act, c
About to invoke thread

So, the issue is as follows: a particular execution "i" of thread S acts upon the updates values as done in the following

Code:

db_Lock();
update_status( Messages[k][0], 1);
db_UnLock();

So, in the aforementioned example, 2nd_val could not be updated and hence execution "i" of thread S will not consider this value. Only its "i+1" execution.

thanks,

I am very sorry, i'm confused.
What is the value for c and Messages[k][2] in the iteration?

Let me ask one straight question.
Put the K value as per below in the printf statement and let us know the behaviour

Code:

printf("About to invoke thread, When k = %u\n",k);
ret = invoke_thread_S();

And check the value of K before "invoke_thread_S" function gets called.

Originally Posted by zahid990170

I am calling another function that wakes a thread S, and then thread S carries on its execution.

Will your "update_status" function does the same functionality of "invoke_thread_S" function?
I mean "update_status" function also have code to wakes a thread S?

Originally Posted by grumpy

Add a statement "fflush(stdout)" immediately before calling invoke_thread_S().

That would fix the problem unless there is another thread active (e.g. from a preceding call of invoke_thread_S() that has not run to completion). If there is another thread active, you need to learn about thread synchronisation (and the need to protect global resources, such as stdout, using synchronisation - a mutex, critical section, or whatever).

thanks grumpy,
I checked with this particular example and it did solve the problem. I will keep checking my program with various runs to see if there is another more complicated issue. And, write it back.

Originally Posted by ArunS

Will your "update_status" function does the same functionality of "invoke_thread_S" function?
I mean "update_status" function also have code to wakes a thread S?

thanks ArunS,

the problem seems to have been solved by using fflush(stdout),

I was not clear in my writing.
"Invoke_thread_S" invokes a thread.
"update_status" only updates the status of a value in the database.
The computation that is performed by thread S, will take into account the values that have been "updated".
My problem was that, some values could be updated "in time" for thread S to work on them, while others were being updated only after the desired iteration of thread S was done.

thanks,