相关疑难解决方法(0)

我想知道使用POSIX调用pthread_once()和/ sem_wait()或dispatch_*函数会更好/更快,所以我创建了一个小测试并对结果感到惊讶(问题和结果在最后).

在测试代​​码中,我使用mach_absolute_time()来为调用计时.我真的不在乎这与纳秒没有完全匹配; 我正在将这些值相互比较,因此确切的时间单位无关紧要,只有间隔之间的差异.结果部分中的数字是可重复的而不是平均数; 我可以平均时间,但我不是在寻找确切的数字.

test.m(简单的控制台应用程序;易于编译):

#import <Foundation/Foundation.h>
#import <dispatch/dispatch.h>
#include <semaphore.h>
#include <pthread.h>
#include <time.h>
#include <mach/mach_time.h>  

// *sigh* OSX does not have pthread_barrier (you can ignore the pthread_barrier 
// code, the interesting stuff is lower)
typedef int pthread_barrierattr_t;
typedef struct
{
    pthread_mutex_t mutex;
    pthread_cond_t cond;
    int count;
    int tripCount;
} pthread_barrier_t;


int pthread_barrier_init(pthread_barrier_t *barrier, const pthread_barrierattr_t *attr, unsigned int count)
{
    if(count == 0)
    {
        errno = EINVAL;
        return -1;
    }
    if(pthread_mutex_init(&barrier->mutex, 0) < 0) …

我有一个在Linux上编译好的脚本(Ubuntu 11.04),但在OS X(Lion)上却没有.

gcc -pthread -o hw1 hw1.c 
hw1.c:22: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘barr’
hw1.c: In function ‘__syncthreads’:
hw1.c:53: error: ‘barr’ undeclared (first use in this function)
hw1.c:53: error: (Each undeclared identifier is reported only once
hw1.c:53: error: for each function it appears in.)
hw1.c:54: error: ‘PTHREAD_BARRIER_SERIAL_THREAD’ undeclared (first use in this function)
hw1.c: In function ‘parallel_psum’:
hw1.c:94: error: ‘barr’ undeclared (first use in this function)
hw1.c:107: warning: assignment from incompatible pointer type

这是代码的前22行:

#include …