Linux下使用者態自旋鎖的實現

#include <stdint.h>#include <assert.h>#include <stdio.h>#include <pthread.h>#include <unistd.h>#define SPIN_LOCK       1static uint32_t atomic_cmp_set(uint32_t *lock, uint32_t old, uint32_t set){    uint8_t rslt = 0;    asm volatile ("lock;" // lock if SMP                  "cmpxchgl %3, %1;"                  "sete %0;"                  : "=a" (rslt)                  : "m" (*lock), "a" (old), "r" (set)                  : "cc", "memory");    return rslt;}static uint32_t g_continue = 1;static volatile uint32_t g_count1 = 0;static volatile uint32_t g_count2 = 0;static uint32_t g_lock = 0;static void *thread_func(void *p_param){    while (g_continue) {    #if SPIN_LOCK        while (!atomic_cmp_set(&g_lock, 0, 1)) {            sched_yield();        }    #endif         ++g_count1;        ++g_count2;     #if SPIN_LOCK        g_lock = 0;    #endif    }    return NULL;}int main(int argc, char *argv[]){    pthread_t t1 = 0, t2 = 0;    pthread_create(&t1, NULL, &thread_func, NULL);    pthread_create(&t2, NULL, &thread_func, NULL);    sleep(1);    g_continue = 0;    pthread_join(t1, NULL);    pthread_join(t2, NULL);    fprintf(stderr,            "%u, %u\n",            g_count1,            g_count2);    return 0;}####################################################################################################################################################################################增加進程同步#include <stdint.h>#include <stdlib.h>#include <stdio.h>#include <assert.h>#include <stdio.h>#include <pthread.h>#include <unistd.h>#include <sys/shm.h>#include <sys/wait.h>#define THREAD          0#define SPIN_LOCK       1#if SPIN_LOCKstatic uint32_t atomic_cmp_set(uint32_t *lock, uint32_t old, uint32_t set){    uint8_t rslt = 0;    assert(NULL != lock);    asm volatile ("lock;" // lock if SMP                  "cmpxchgl %3, %1;"                  "sete %0;"                  : "=a" (rslt)                  : "m" (*lock), "a" (old), "r" (set)                  : "cc", "memory");    return rslt;}#endif#if THREADstatic uint32_t g_continue = 1;#elsestatic void *gp_continue = NULL;#endif#if THREADstatic volatile uint32_t g_count1 = 0;static volatile uint32_t g_count2 = 0;#elsestatic volatile void *gp_count1 = 0;static volatile void *gp_count2 = 0;#endifstatic int shmid = 0;#if SPIN_LOCK#if THREADstatic uint32_t g_lock = 0;#elsestatic void *gp_lock = NULL;#endif#endifstatic void *thread_func(void *p_param){#if THREAD    while (g_continue) {#else    while (*(uint32_t *)gp_continue) {#endif    #if SPIN_LOCK    #if THREAD        while (!atomic_cmp_set(&g_lock, 0, 1)) {    #else        while (!atomic_cmp_set((uint32_t *)gp_lock, 0, 1)) {    #endif            sched_yield();        }    #endif    #if THREAD        ++g_count1;        ++g_count2;    #else        ++(*(volatile uint32_t *)gp_count1);        ++(*(volatile uint32_t *)gp_count2);    #endif    #if SPIN_LOCK    #if THREAD        g_lock = 0;    #else        *(uint32_t *)gp_lock = 0;    #endif /* THEAD */    #endif    }#if SPIN_LOCK#if !THREAD    shmdt(gp_lock);#endif#endif    return NULL;}int main(int argc, char *argv[]){    // 建立共用記憶體    shmid = shmget(IPC_PRIVATE, 4096, IPC_CREAT | 0600);    if (-1 == shmid) {        return -1;    }#if THREAD    pthread_t t1 = 0, t2 = 0;    pthread_create(&t1, NULL, &thread_func, NULL);    pthread_create(&t2, NULL, &thread_func, NULL);    sleep(1);    g_continue = 0;    pthread_join(t1, NULL);    pthread_join(t2, NULL);#else#if SPIN_LOCK    gp_lock = shmat(shmid, 0, 0);    *(uint32_t *)gp_lock = 0;#endif    gp_continue = ((char *)shmat(shmid, 0, 0)) + 4;    *(uint32_t *)gp_continue = 1;    gp_count1 = ((char *)shmat(shmid, 0, 0)) + 8;    *(uint32_t *)gp_count1 = 0;    gp_count2 = ((char *)shmat(shmid, 0, 0)) + 12;    *(uint32_t *)gp_count2 = 0;    switch (fork()) {    case 0:        break;    case -1:        exit(-1);    default:        {            int x = fork();            if (x > 0) {                sleep(1);                *(uint32_t *)gp_continue = 0;                wait(NULL);                shmdt(gp_continue);                (void)shmctl(shmid, IPC_RMID, 0);                exit(0);            }        }    }    thread_func(NULL);#endif    fprintf(stderr,            "%u, %u\n",        #if THREAD            g_count1,            g_count2);        #else            *(volatile uint32_t *)gp_count1,            *(volatile uint32_t *)gp_count2);        #endif    return 0;}

ps: 彙編代碼源自nginx，CAS機制只能實現自旋鎖，因為使用者態無法掛起喚醒線程，可以藉助futex實現互斥鎖。