Creating an array to hold posix thread ids: Only dynamic array works


Login or Register for Dates, Times and to Reply

 
Thread Tools Search this Thread
# 1  
Creating an array to hold posix thread ids: Only dynamic array works

I am facing a strange error while creating posix threads:
Given below are two snippets of code, the first one works whereas the second one gives a garbage value in the output.

Snippet 1
This works:
--------------
int *threadids;
threadids = (int *) malloc (num_threads * sizeof(int));

for(i = 0; i<num_threads; i++)
threadids[i] = i;

for(i=0; i<num_threads; i++)
pthread_create(&threads[i], NULL, pthread_init, &threadids[i]);

.
.
void *pthread_init(void *threadid)
{
int tid;
tid = (int)(*(int *)threadid));
printf("Thread id is %d", tid);
pthread_exit(NULL);
}

Output: Thread id is 0
--------------

Snippet 2
This doesn't work:
--------------
int threadids[num_threads];
for(i = 0; i<num_threads; i++)
threadids[i] = i;
.
.
.
Output: Thread id is 634800
--------------

As you can see, the only difference is in the way the array threadids is declared. But the second snippet gives a garbage value.

I will be glad if someone points out whats going wrong with the first snippet. Thanks.
# 2  
Where is this code called from?
I guess from some function.
In this case first example works fine becuase dynamically allocated threadids exists beyond this fucntion, but it second example it dies immediately.
Remember, pthread_create doesn't wait for actual start-up of new thread.
# 3  
I am not sure I understand. But you were right, if the above code is placed in the main() function, it works fine, but if I place it in a separate function and call this function from main(), it gives the garbage output.

But I am still not quite sure why it shouldn't work. As you said, first example works fine becuase dynamically allocated threadids exists beyond this fucntion, but it second example it dies immediately. So, shouldnt I face a problem when I place the code directly in the main() function ?? The threadids could die immediately again before the thread is actually spawned, in which case it picks up a garbage output.

Thanks.
# 4  
Quote:
Originally Posted by kmehta
So, shouldnt I face a problem when I place the code directly in the main() function ??
It depends on operating system. In case of Solaris your new thread might not even start before your application ends up.
The basic idea is that pointer your pass to pthread_create must eixsts at the moment you thread starts-up. And if you plan to use this data in this thread (otherwise why do you pass it?) you must guarantee that this data is not being destroyed while your thread is running. Usually people use prthread_join for this purpose.
# 5  
I get it.

Thanks a lot for your help. -- Kshitij
Login or Register for Dates, Times and to Reply

Previous Thread | Next Thread
Thread Tools Search this Thread
Search this Thread:
Advanced Search

10 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

Creating a pseudo-array in dash, (POSIX).

Arrays in dash, (POSIX). Hi gurus... I am thinking of trying AudioScope.sh in pure POSIX so... I need an array in dash, I know it is not possible but pseudo-arrays are. I have two versions that work, the second is an idea from the WWW. The first is what I would like to use. There are... (8 Replies)
Discussion started by: wisecracker
8 Replies

2. Programming

readdir and dynamic array memory corruption

Hi everyone I am developing an utility. At some part of it I read directory entries to a dynamic array: struct list It stores pointers to items: list.entries, which are structures: struct entry If a number of files in a directory is greater then number of elements an array was initially... (11 Replies)
Discussion started by: torbium
11 Replies

3. Shell Programming and Scripting

Assigning values for a dynamic array for an input

Hello, Can somebody please give me a snippet for the below requirement. I want to assign the values separeted by a comma to be assigned to a dynamic array. If I give an input (read statement) like abc1,abc2,abc3,abc4,abc5, all these strings abc* should be assigned to an array like below... (2 Replies)
Discussion started by: suneelj
2 Replies

4. Shell Programming and Scripting

dynamic index for array in while loop

Hi, I'm just trying to use a dynamic index for some array elements that I'm accessing within a loop. Specifically, I want to access an array at variable position $counter and then also at location $counter + 1 and $counter + 2 (the second and third array positions after it) but I keep getting... (0 Replies)
Discussion started by: weak_code-fu
0 Replies

5. Programming

array dynamic allocation

Hi, I have the following problem: i must allocate a dynamic array from a subroutine which should return such array to main function. The subroutine has already a return parameter so i thought of pass the array as I/O parameter. I tried the following program but it doesn't work (segmentation... (11 Replies)
Discussion started by: littleboyblu
11 Replies

6. Shell Programming and Scripting

creating a dynamic array

i want to create an array the array elements are populated depending upon the number of entries present in a data file The data file is created dynamically how to achieve the same thanks (1 Reply)
Discussion started by: trichyselva
1 Replies

7. Shell Programming and Scripting

How to hold string array in shell scripts

Gents, Below is the Shell script which I am trying to hold a string of array that is passed from a java file. But it is not working . Can any one please help me to by fixing it. #!/bin/csh/ set copy = ($argv) echo $copy >> /home/users/bavananr/rrr.log echo $copy >>... (3 Replies)
Discussion started by: brajesh
3 Replies

8. Shell Programming and Scripting

Dynamic Array Issue

Could one of you, please, provide some input regarding my problem below and it is as follows: I have 2 files that I need to make sure are identical before processing: First, I sort both files Second, I do a diff file1 file2 > File 3 This provides me with the difference. Now, I need to... (6 Replies)
Discussion started by: ddedic
6 Replies

9. UNIX for Advanced & Expert Users

MAX SIZE ARRAY Can Hold it

Hi, Do anyone know what's the max size of array (in awk) can be store before hit any memory issue. Regards (3 Replies)
Discussion started by: epall
3 Replies

10. Shell Programming and Scripting

creating a dynamic array in ksh

Hi, Is it possible to create a dynamic array in shell script. I am trying to get the list of logfiles that created that day and put it in a dynamic array. I am not sure about it. help me New to scripting Gundu (3 Replies)
Discussion started by: gundu
3 Replies

Featured Tech Videos