私は学校の研究室で働いており、カウント プログラム用の再帰的ミューテックス ロックを作成するように指示されています。私はいくつかのコードを書きましたが (これは動作しません)、再帰的ミューテックス ロックを使用する背後にある本当のアイデアを理解していないことが主な原因だと思います。再帰的なミューテックスロックが何をすべきか/どのように見えるべきかを誰か詳しく説明できますか?
一般的な注意: 私は答えを求めているのではなく、再帰的相互排他ロックが何をすべきかについての説明を求めているだけです。
また、誰かが興味を持っている場合は、これに必要なコードを次に示します。私が編集/実装しているコードは recmutex.c です。
remutex.h
#include <pthread.h>
/*
* The recursive_mutex structure.
*/
struct recursive_mutex {
pthread_cond_t cond;
pthread_mutex_t mutex; //a non-recursive pthread mutex
pthread_t owner;
unsigned int count;
unsigned int wait_count;
};
typedef struct recursive_mutex recursive_mutex_t;
/* Initialize the recursive mutex object.
*Return a non-zero integer if errors occur.
*/
int recursive_mutex_init (recursive_mutex_t *mu);
/* Destroy the recursive mutex object.
*Return a non-zero integer if errors occur.
*/
int recursive_mutex_destroy (recursive_mutex_t *mu);
/* The recursive mutex object referenced by mu shall be
locked by calling pthread_mutex_lock(). When a thread
successfully acquires a mutex for the first time,
the lock count shall be set to one and successfully return.
Every time a thread relocks this mutex, the lock count
shall be incremented by one and return success immediately.
And any other calling thread can only wait on the conditional
variable until being waked up. Return a non-zero integer if errors occur.
*/
int recursive_mutex_lock (recursive_mutex_t *mu);
/* The recursive_mutex_unlock() function shall release the
recursive mutex object referenced by mu. Each time the owner
thread unlocks the mutex, the lock count shall be decremented by one.
When the lock count reaches zero, the mutex shall become available
for other threads to acquire. If a thread attempts to unlock a
mutex that it has not locked or a mutex which is unlocked,
an error shall be returned. Return a non-zero integer if errors occur.
*/
int recursive_mutex_unlock (recursive_mutex_t *mu);
recmutex.c: 再帰的ミューテックスの関数が含まれています
#include <stdio.h>
#include <pthread.h>
#include <errno.h>
#include "recmutex.h"
int recursive_mutex_init (recursive_mutex_t *mu){
int err;
err = pthread_mutex_init(&mu->mutex, NULL);
if(err != 0){
perror("pthread_mutex_init");
return -1;
}else{
return 0;
}
return 0;
}
int recursive_mutex_destroy (recursive_mutex_t *mu){
int err;
err = pthread_mutex_destroy(&mu->mutex);
if(err != 0){
perror("pthread_mutex_destroy");
return -1;
}else{
return 1;
}
return 0;
}
int recursive_mutex_lock (recursive_mutex_t *mu){
if(mutex_lock_count == 0){
pthread_mutex_lock(&mu->mutex);
mu->count++;
mu->owner = pthread_self();
printf("%s", mu->owner);
return 0;
}else if(mutex_lock_count > 0){
pthread_mutex_lock(&mu->mutex);
mu->count++;
mu->owner = pthread_self();
return 0;
}else{
perror("Counter decremented incorrectly");
return -1;
}
}
int recursive_mutex_unlock (recursive_mutex_t *mu){
if(mutex_lock_count <= 0){
printf("Nothing to unlock");
return -1;
}else{
mutex_lock_count--;
pthread_mutex_unlock(&mu->mutex);
return 0;
}
}
count_recursive.cc: 上記のカウント プログラム。recmutex 関数を使用します。
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include "recmutex.h"
//argument structure for the thread
typedef struct _arg_{
int n1;
int n2;
int ntimes;
}Arg;
int count; //global counter
recursive_mutex_t mutex; //the recursive mutex
void do_inc(int n){
int ret;
if(n == 0){
return;
}else{
int c;
ret = recursive_mutex_lock(&mutex);
assert(ret == 0);
c = count;
c = c + 1;
count = c;
do_inc(n - 1);
ret = recursive_mutex_unlock(&mutex);
assert(ret == 0);
}
}
/* Counter increment function. It will increase the counter by n1 * n2 * ntimes. */
void inc(void *arg){
Arg * a = (Arg *)arg;
for(int i = 0; i < a->n1; i++){
for(int j = 0; j < a->n2; j++){
do_inc(a->ntimes);
}
}
}
int isPositiveInteger (const char * s)
{
if (s == NULL || *s == '\0' || isspace(*s))
return 0;
char * p;
int ret = strtol (s, &p, 10);
if(*p == '\0' && ret > 0)
return 1;
else
return 0;
}
int test1(char **argv){
printf("==========================Test 1===========================\n");
int ret;
//Get the arguments from the command line.
int num_threads = atoi(argv[1]); //The number of threads to be created.
int n1 = atoi(argv[2]); //The outer loop count of the inc function.
int n2 = atoi(argv[3]); //The inner loop count of the inc function.
int ntimes = atoi(argv[4]); //The number of increments to be performed in the do_inc function.
pthread_t *th_pool = new pthread_t[num_threads];
pthread_attr_t attr;
pthread_attr_init( &attr );
pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
ret = recursive_mutex_init(&mutex);
assert(ret == 0);
printf("Start Test. Final count should be %d\n", num_threads * n1 * n2 * ntimes );
// Create threads
for(int i = 0; i < num_threads; i++){
Arg *arg = (Arg *)malloc(sizeof(Arg));
arg->n1 = n1;
arg->n2 = n2;
arg->ntimes = ntimes;
ret = pthread_create(&(th_pool[i]), &attr, (void * (*)(void *)) inc, (void *)arg);
assert(ret == 0);
}
// Wait until threads are done
for(int i = 0; i < num_threads; i++){
ret = pthread_join(th_pool[i], NULL);
assert(ret == 0);
}
if ( count != num_threads * n1 * n2 * ntimes) {
printf("\n****** Error. Final count is %d\n", count );
printf("****** It should be %d\n", num_threads * n1 * n2 * ntimes );
}
else {
printf("\n>>>>>> O.K. Final count is %d\n", count );
}
ret = recursive_mutex_destroy(&mutex);
assert(ret == 0);
delete [] th_pool;
return 0;
}
int foo(){
int ret;
printf("Function foo\n");
ret = recursive_mutex_unlock(&mutex);
assert(ret != 0);
return ret;
}
//test a thread call unlock without actually holding it.
int test2(){
int ret;
printf("\n==========================Test 2==========================\n");
pthread_t th;
pthread_attr_t attr;
pthread_attr_init( &attr );
pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
ret = recursive_mutex_init(&mutex);
ret = pthread_create(&th, &attr, (void * (*)(void *))foo, NULL);
printf("Waiting for thread to finish\n");
ret = pthread_join(th, NULL);
assert(ret == 0);
return 0;
}
int main( int argc, char ** argv )
{
int ret;
count = 0;
if( argc != 5 ) {
printf("You must enter 4 arguments. \nUsage: ./count_recursive num_threads n1 n2 ntimes\n");
return -1;
}
if(isPositiveInteger(argv[1]) != 1 || isPositiveInteger(argv[2]) != 1 || isPositiveInteger(argv[3]) != 1 || isPositiveInteger(argv[4]) != 1 ){
printf("All the 4 arguments must be positive integers\n");
return -1;
}
test1(argv);
test2();
return 0;
}