StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POSemaphore waiting case
primarykey
Id
14055933
data
AcceptedAnswerId
14058391
AnswerCount
2
ClosedDate
2012-12-29T03:34:47.900
CommentCount
5
CommunityOwnedDate
CreationDate
2012-12-27T14:04:38.230
FavoriteCount
0
LastActivityDate
2012-12-27T17:07:05.310
LastEditDate
LastEditorUserId
0
OwnerUserId
1388172
ParentId
0
PostTypeId
1
Score
0
ViewCount
504
LastEditorDisplayName
text
Body
I want to make sure my sempahore do what I expect to do, but I can't bring it to the state where one or more threads wait. I need that only 3 threads at a time to be able to work over the linked list. code: <pre><code>#include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <unistd.h> #include <math.h> #include <semaphore.h> struct dataBlock{ struct node *root; int listSize; int forIndex; }; struct node { // std linked list node int value; int worker; struct node *next; }; int limit = 5; sem_t sem; pthread_mutex_t mutp = PTHREAD_MUTEX_INITIALIZER; // mutex pthread_cond_t condvar = PTHREAD_COND_INITIALIZER; //condvar void *deleteDoneNodes(struct node *n){ struct node *root = n; struct node *it = root; struct node *prev = NULL; do{ if(it->value == 1){ struct node *next = it->next; if (prev != NULL) { prev->next = next; } if (it == root) { root = next; } free(it); it = next; } else { prev = it; it = it->next; } }while(it != NULL); return root; } void * worker( void *data ){ //get list int wFlag; struct dataBlock *inData = ( struct dataBlock * ) data; struct node *root = inData->root; int forIndex = inData ->forIndex; free(data); while(1){ if( sem_wait( &sem ) != 0 ){ printf( " > waiting... \n" ); } // pthread_mutex_lock( &mutp ); struct node *it = root; do{ if( forIndex == it->worker ){ if( it->value > 2 ){ while( it->value != 1 ) it->value = sqrt(it->value); } } else{ // printf("Not sqrt-able node %d\n",it->value); } it = it->next; }while(it != NULL); // pthread_cond_signal( &condvar ); // pthread_mutex_unlock( &mutp ); sem_post(&sem); // sleep(100); // "create" concurrancy envi. pthread_exit(0); } return NULL; } int main( int argc, char *argv[] ){ if ( argc != 3 ){ printf( "Programm must be called with \n NR of elements and NR of workers! \n " ); exit( 1 ); } int i; struct node *root; struct node *iterator; //prepare list for task int listSize = atoi(argv[1]); int nrWorkers = atoi(argv[2]); root = malloc(sizeof( struct node) ); root->value = rand() % 100; root->worker = 0; iterator = root; for( i=1; i<listSize; i++ ){ iterator->next = malloc(sizeof(struct node)); iterator = iterator->next; iterator->value = rand() % 100; iterator->worker = i % nrWorkers; printf("node #%d worker: %d value: %d\n", i, iterator->worker,iterator->value); } iterator->next = NULL; printf("? List got populated\n"); // init semaphore > keeps max 3 threads working over the list if( sem_init(&sem,0,3) < 0){ perror("semaphore initilization"); exit(0); } // Create all threads to parse the link list int ret; pthread_mutex_init(&mutp,NULL); pthread_t w_thread; pthread_t* w_threads = malloc(nrWorkers * sizeof(w_thread)); for( i=0; i < nrWorkers; i++ ){ struct dataBlock *data = malloc(sizeof(struct dataBlock)); data->root = root; data->listSize = listSize; data->forIndex = i; ret = pthread_create ( &w_threads[i], NULL, worker, (void *) data ); if( ret ) { perror("Thread creation fail"); exit(2); } } deleteDoneNodes( root ); int join; for ( i = 0; i < nrWorkers; i++ ){ join = pthread_join(w_threads[i],NULL); } iterator = root; for ( i = 0; i < listSize; i++){ printf("val: %d worker: %d _ \n", iterator->value, iterator->worker); iterator = iterator->next; } free(root); free(iterator); sem_destroy(&sem); return 0; } </code></pre> terminal~> ./s 16 16 <pre><code>node #1 worker: 1 value: 86 node #2 worker: 2 value: 77 node #3 worker: 3 value: 15 node #4 worker: 4 value: 93 node #5 worker: 5 value: 35 node #6 worker: 6 value: 86 node #7 worker: 7 value: 92 node #8 worker: 8 value: 49 node #9 worker: 9 value: 21 node #10 worker: 10 value: 62 node #11 worker: 11 value: 27 node #12 worker: 12 value: 90 node #13 worker: 13 value: 59 node #14 worker: 14 value: 63 node #15 worker: 15 value: 26 ? List got populated val: 1 worker: 0 _ val: 1 worker: 1 _ val: 1 worker: 2 _ val: 1 worker: 3 _ val: 1 worker: 4 _ val: 1 worker: 5 _ val: 1 worker: 6 _ val: 1 worker: 7 _ val: 1 worker: 8 _ val: 1 worker: 9 _ val: 1 worker: 10 _ val: 1 worker: 11 _ val: 1 worker: 12 _ val: 1 worker: 13 _ val: 1 worker: 14 _ val: 1 worker: 15 _ </code></pre>
Tags
<c><pthreads><semaphore>
Title
Semaphore waiting case
singulars
PostAcceptedAnswerId
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. This table or related slice is empty.
UserOwnerUserId
1. USBogdan M.
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
2. PO
 singulars
 PostTypePostTypeId
 PTAnswer
VotesPostIdCreationDate
1. VO
 singulars
 PostPostId
 POSemaphore waiting case
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTDownMod
CommentsPostId

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.