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Microsoft Interview Question for Software Engineer / Developers


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http://doc.trolltech.com/qq/qq11-mutex.html

- Anonymous May 11, 2009 | Flag Reply
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This is a nice solution ! Thanks for sharing...

- Ashish Kaila March 12, 2011 | Flag
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Hi, what do you mean by upgrade/downgrade of locks?

Thanks!

- Anonymous November 06, 2009 | Flag Reply
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can you please elaborate the question ? in terms of exactly what they expected you to code.

- anon December 22, 2009 | Flag Reply
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can you please elaborate the question ? in terms of exactly what they expected you to code.

- anon December 22, 2009 | Flag Reply
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of 0 vote

its about reader writer problem in a library .. it can be solved using mutex/semaphore

- intuidev January 21, 2010 | Flag Reply
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/* pthread implementation of 1st reader/writer problem
 *  based on mutex and conditional variable
*/
typedef struct read_write_lock_s {
   pthread_mutex_t mutex;
   pthread_cond_t cv;
   int read_ctr;
   it  write_ctr;
}read_write_lock;

void rw_lock_init(read_write_lock *rw_lock)
{
  rw_lock->read_ctr = 0;
  rw_lock->write_ctr = 0;
  pthread_cond_init(&rw_lock->cv);
  pthread_mutex_init(&rw_lock->mutex);
}

void rw_lock_acquire_read(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  while(rw_lock->write_ctr != 0) {  /* wait for writer */
    pthread_cond_wait(&rw_lock->cv, &rw_lock->mutex);
  }
  rw_lock->read_ctr++;
  pthread_mutex_unlock(&rw_lock->mutex);
}

void rw_lock_acquire_write(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  while(rw_lock->write_ctr !=0 || rw_lock->read_ctr>0) {
    pthread_cond_wait(&rw_lock->cv, &rw_lock->mutex);
    rw_lock->write_ctr=1;
  }
  pthread_mutex_unlock(&rw_lock->mutex);
}

void rw_lock_release_read(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  if(--rw_lock->read_ctr == 0) { /* no one is reading now; writer please hurry! */
    pthread_cond_broadcast(&rw_lock->cv);
  }
  pthread_mutex_unlock(&rw_lock->mutex);
}

void rw_lock_release_write(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  rw_lock->write_ctr = 0;
  pthread_cond_broadcast(&rw_lock->cv); /* writer is done; readers in... */
  pthread_mutex_unlock(&rw_lock->mutex);
}

- jzhu May 19, 2012 | Flag Reply
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of 0 votes

The idea is correct but the implementation has an issue:

pthread_mutex_lock(&rw_lock->mutex);
  while(rw_lock->write_ctr !=0 || rw_lock->read_ctr>;0) {
    pthread_cond_wait(&rw_lock->cv, &rw_lock->mutex);
    rw_lock->write_ctr=1;
  }

once u set rw_lock->write_ctr=1 u will never get of the while loop.

- kykydyk March 18, 2013 | Flag
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0
of 0 vote

/* pthread implementation of 1st reader/writer problem
 *  based on mutex and conditional variable
*/
typedef struct read_write_lock_s {
   pthread_mutex_t mutex;
   pthread_cond_t cv;
   int read_ctr;
   it  write_ctr;
}read_write_lock;

void rw_lock_init(read_write_lock *rw_lock)
{
  rw_lock->read_ctr = 0;
  rw_lock->write_ctr = 0;
  pthread_cond_init(&rw_lock->cv);
  pthread_mutex_init(&rw_lock->mutex);
}

void rw_lock_acquire_read(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  while(rw_lock->write_ctr != 0) {  /* wait for writer */
    pthread_cond_wait(&rw_lock->cv, &rw_lock->mutex);
  }
  rw_lock->read_ctr++;
  pthread_mutex_unlock(&rw_lock->mutex);
}

void rw_lock_acquire_write(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  while(rw_lock->write_ctr !=0 || rw_lock->read_ctr>0) {
    pthread_cond_wait(&rw_lock->cv, &rw_lock->mutex);
    rw_lock->write_ctr=1;
  }
  pthread_mutex_unlock(&rw_lock->mutex);
}

void rw_lock_release_read(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  if(--rw_lock->read_ctr == 0) { /* no one is reading now; writer please hurry! */
    pthread_cond_broadcast(&rw_lock->cv);
  }
  pthread_mutex_unlock(&rw_lock->mutex);
}

void rw_lock_release_write(read_write_lock *rw_lock)
{
  pthread_mutex_lock(&rw_lock->mutex);
  rw_lock->write_ctr = 0;
  pthread_cond_broadcast(&rw_lock->cv); /* writer is done; readers in... */
  pthread_mutex_unlock(&rw_lock->mutex);
}

- jzhu May 19, 2012 | Flag Reply


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