Reader Writer Problem C thread implementation Linux platform

1. First, the reader's semaphore implementation

Set three mutex semaphores:

• Rwmutex is used to access Shared data that is mutually exclusive to other readers/writers.
• Rmutex is used to access the reader counter readcount that is mutually exclusive to the reader.
• Wmutex is used by the writer to wait for the reader to exit.

• VaR rwmutex, rmutex, wmutex: semaphore: =, 1; int readcount = 0; cobegin readeri begin // I = ,.... P (rwmutex); P (rmutex); readcount ++; If (readcount = 1) P (wmutex); // a reader enters and a mutex write operation V (rmutex ); V (rwmutex); // release the read/write mutex semaphores in time to allow other read and write processes to apply for resource read data; P (rmutex); readcount --; If (readcount = 0) V (wmutex); // all readers exit and allow write update V (rmutex); End writerj begin // J = ,.... P (rwmutex); // mutex is followed by other readers and writers P (wmutex); // If a reader is reading, wait for all readers to finish writing updates; V (wmutex ); // allow the next new reader to enter the next mutex write operation V (rwmutex); // allow the subsequent new reader and other writers to endcoend

  2. on the Linux platform, I used pthread_creat, pthread_mutex_trylock, and pthread_mutex_unlock;

  There must be bugs in code implementation. If you want to pass by, you may criticize and correct them.

  # Include <stdlib. h> # include <stdlib. h>/* For convenience */# include <stddef. h>/* For offsetof */# include <string. h>/* For convenience */# include <unistd. h>/* For convenience */# include <signal. h>/* For sig_err */# include <time. h> # include <pthread. h> pthread_mutex_t rwlock = pthread_mutex_initializer;/* Mutual Exclusion of buffer access */pthread_mutex_t rlock = pthread_mutex_initializer;/* Mutual Exclusion of readcount access */pthread_mutex _ T wlock = pthread_mutex_initializer;/* write thread access mutex */INT readcount; int readpos, writepos; const int n = 10; int pool [10]; pthread_t pthreadarray [10]; void print () {int I; printf ("\ n and now the pool is \ n"); for (I = 0; I <n; I ++) printf ("% d is: % d \ n", I, pool [I]); sleep (2);} pthread_t find (pthread_t tid) {int I; for (I = 0; I <n; I ++) if (pthreadarray [I] = tid) return I; Return-1;} void * R Ead_fn (void * Arg) {pthread_t tid; For (;) {pthread_mutex_trylock (& rwlock); pthread_mutex_trylock (& rlock); readcount ++; If (readcount = 1) pthread_mutex_trylock (& wlock); tid = pthread_self (); printf ("\ n *********************************** * *************************** \ n \ now is read thread reading and the number is % d, TID is % LD \ n \ The pool POS is % d and content is % d \ n ", find (TID), (long) tid, rea DPOs, pool [readpos]); print (); pool [readpos] =-1; readpos = (readpos + 1) % N; readcount --; pthread_mutex_unlock (& rlock ); if (readcount = 0) pthread_mutex_unlock (& wlock); pthread_mutex_unlock (& rwlock) ;}} void * write_fn (void * Arg) {int val; pthread_t tid; for (;) {pthread_mutex_trylock (& rwlock); pthread_mutex_trylock (& wlock); val = rand (); tid = pthread_self (); printf ("\ n ***************************** * ********************************* \ N \ now is write thread writing and the number is % d, TID is % LD \ n \ The pool POS is % d and content is % d \ n ", find (TID), (long) tid, writepos, Val ); pool [writepos] = val; writepos = (writepos + 1) % N; pthread_mutex_unlock (& wlock); pthread_mutex_unlock (& rwlock); print () ;}} void Init () {int I; for (I = 0; I <10; I ++) pool [I] =-1;} int main () {Init (); pthread_t thr1, THR 2, thr3, thr4; int I = 0; srand (INT) time (0);/* pthread_create (& thr1, null, write_fn, null ); printf ("the thread is wirte and TID is % d \ n", (INT) thr1); pthread_create (& thr2, null, read_fn, null ); printf ("the thread is read and TID is % d \ n", (INT) thr2); pthread_create (& thr3, null, read_fn, null ); printf ("the thread is read and TID is % d \ n", (INT) thr3); pthread_create (& thr4, null, write_fn, null); printf ("The threa D is wirte and TID is % d \ n ", (INT) thr4); */for (I = 0; I <10; I ++) {if (I % 3! = 0) {pthread_create (& pthreadarray [I], null, write_fn, null); printf ("START: The % d thread is wirte and TID is % LD \ n ", i, (long) pthreadarray [I]);} else {pthread_create (& pthreadarray [I], null, read_fn, null); printf ("start: the % d thread is read and TID is % LD \ n ", I, (long) pthreadarray [I]) ;}} sleep (10); exit (0 );}

  Reference: http://blog.csdn.net/lenic/article/details/4675142address of my independent blog: http://www.fuxiang90.me /? P = 314 welcome