C語(yǔ)言多線程開(kāi)發(fā)中死鎖與讀寫(xiě)鎖問(wèn)題詳解

第C語(yǔ)言多線程開(kāi)發(fā)中死鎖與讀寫(xiě)鎖問(wèn)題詳解目錄死鎖讀寫(xiě)鎖

死鎖

有時(shí)，一個(gè)線程需要同時(shí)訪問(wèn)兩個(gè)或更多不同的共享資源，而每個(gè)資源又都由不同的互斥量管理。當(dāng)超過(guò)一個(gè)線程加鎖同一組互斥量時(shí)，就有可能發(fā)生死鎖；

兩個(gè)或兩個(gè)以上的進(jìn)程在執(zhí)行過(guò)程中，因爭(zhēng)奪共享資源而造成的一種互相等待的現(xiàn)象，若無(wú)外力作用，它們都將無(wú)法推進(jìn)下去。此時(shí)稱系統(tǒng)處于死鎖狀態(tài)或系統(tǒng)產(chǎn)生了死鎖。

死鎖的幾種場(chǎng)景：

忘記釋放鎖重復(fù)加鎖（重復(fù)加相同的鎖）多線程多鎖，搶占鎖資源

//多線程多鎖，搶占鎖資源

#includestdio.h

#includepthread.h

#includeunistd.h

//創(chuàng)建2個(gè)互斥量

pthread_mutex_tmutex1,mutex2;

void*workA(void*arg){

pthread_mutex_lock(mutex1);

sleep(1);

pthread_mutex_lock(mutex2);

printf("workA....\n");

pthread_mutex_unlock(mutex2);

pthread_mutex_unlock(mutex1);

returnNULL;

void*workB(void*arg){

pthread_mutex_lock(mutex2);

sleep(1);

pthread_mutex_lock(mutex1);

printf("workB....\n");

pthread_mutex_unlock(mutex1);

pthread_mutex_unlock(mutex2);

returnNULL;

intmain(){

//初始化互斥量

pthread_mutex_init(mutex1,NULL);

pthread_mutex_init(mutex2,NULL);

//創(chuàng)建2個(gè)子線程

pthread_ttid1,tid2;

pthread_create(tid1,NULL,workA,NULL);

pthread_create(tid2,NULL,workB,NULL);

//回收子線程資源

pthread_join(tid1,NULL);

pthread_join(tid2,NULL);

//釋放互斥量資源

pthread_mutex_destroy(mutex1);

pthread_mutex_destroy(mutex2);

return0;

}

執(zhí)行結(jié)果：

讀寫(xiě)鎖

/*

讀寫(xiě)鎖的類型pthread_rwlock_t

intpthread_rwlock_init(pthread_rwlock_t*restrictrwlock,constpthread_rwlockattr_t*restrictattr);

intpthread_rwlock_destroy(pthread_rwlock_t*rwlock);

intpthread_rwlock_rdlock(pthread_rwlock_t*rwlock);

intpthread_rwlock_tryrdlock(pthread_rwlock_t*rwlock);

intpthread_rwlock_wrlock(pthread_rwlock_t*rwlock);

intpthread_rwlock_trywrlock(pthread_rwlock_t*rwlock);

intpthread_rwlock_unlock(pthread_rwlock_t*rwlock);

案例：8個(gè)線程操作同一個(gè)全局變量。

3個(gè)線程不定時(shí)寫(xiě)這個(gè)全局變量，5個(gè)線程不定時(shí)的讀這個(gè)全局變量

#includestdio.h

#includepthread.h

#includeunistd.h

//創(chuàng)建一個(gè)共享數(shù)據(jù)

intnum=1;

//pthread_mutex_tmutex;

pthread_rwlock_trwlock;

void*writeNum(void*arg){

while(1){

pthread_rwlock_wrlock(rwlock);

num++;

printf("++write,tid:%ld,num:%d\n",pthread_self(),num);

pthread_rwlock_unlock(rwlock);

usleep(100);

returnNULL;

void*readNum(void*arg){

while(1){

pthread_rwlock_rdlock(rwlock);

printf("===read,tid:%ld,num:%d\n",pthread_self(),num);

pthread_rwlock_unlock(rwlock);

usleep(100);

returnNULL;

intmain(){

pthread_rwlock_init(rwlock,NULL);

//創(chuàng)建3個(gè)寫(xiě)線程，5個(gè)讀線程

pthread_twtids[3],rtids[5];

for(inti=0;ii++){

pthread_create(wtids[i],NULL,writeNum,NULL);

for(inti=0;ii++){

pthread_create(rtids[i],NULL,readNum,NULL);

//設(shè)置線程分離

for(inti=0;ii++){

pthread_detach(wtids[i]);

for(inti=0;ii