自学教程：C++ xchg函数代码示例

static void xen_resume_notifier(int _suspend_cancelled){	int old_state = xchg(&shutting_down, SHUTDOWN_RESUMING);	BUG_ON(old_state != SHUTDOWN_SUSPEND);	suspend_cancelled = _suspend_cancelled;}

inline void*    Atomic::xchg_ptr(void*    exchange_value, volatile void*     dest) {  return (void*)xchg((jint)exchange_value, (volatile jint*)dest);}

RT_TRAP_HANDLER rt_set_trap_handler (RT_TRAP_HANDLER handler){	return (RT_TRAP_HANDLER)xchg(&rtai_trap_handler, handler);}

void cv_signal(cond_t *cv){  t_wakeup();  xchg(&cv->cond, 1);}

/* * Expand the fdset in the files_struct.  Called with the files spinlock * held for write. */int expand_fdset(struct files_struct *files, int nr){    fd_set *new_openset = 0, *new_execset = 0;    int error, nfds = 0;    error = -EMFILE;    if (files->max_fdset >= NR_OPEN || nr >= NR_OPEN)        goto out;    nfds = files->max_fdset;    write_unlock(&files->file_lock);    /* Expand to the max in easy steps */    do {        if (nfds < (PAGE_SIZE * 8))            nfds = PAGE_SIZE * 8;        else {            nfds = nfds * 2;            if (nfds > NR_OPEN)                nfds = NR_OPEN;        }    } while (nfds <= nr);    error = -ENOMEM;    new_openset = alloc_fdset(nfds);    new_execset = alloc_fdset(nfds);    write_lock(&files->file_lock);    if (!new_openset || !new_execset)        goto out;    error = 0;    /* Copy the existing tables and install the new pointers */    if (nfds > files->max_fdset) {        int i = files->max_fdset / (sizeof(unsigned long) * 8);        int count = (nfds - files->max_fdset) / 8;        /*         * Don't copy the entire array if the current fdset is         * not yet initialised.         */        if (i) {            memcpy (new_openset, files->open_fds, files->max_fdset/8);            memcpy (new_execset, files->close_on_exec, files->max_fdset/8);            memset (&new_openset->fds_bits[i], 0, count);            memset (&new_execset->fds_bits[i], 0, count);        }        nfds = xchg(&files->max_fdset, nfds);        new_openset = xchg(&files->open_fds, new_openset);        new_execset = xchg(&files->close_on_exec, new_execset);        write_unlock(&files->file_lock);        free_fdset (new_openset, nfds);        free_fdset (new_execset, nfds);        write_lock(&files->file_lock);        return 0;    }    /* Somebody expanded the array while we slept ... */out:    write_unlock(&files->file_lock);    if (new_openset)        free_fdset(new_openset, nfds);    if (new_execset)        free_fdset(new_execset, nfds);    write_lock(&files->file_lock);    return error;}

int expand_fd_array(struct files_struct *files, int nr){    struct file **new_fds;    int error, nfds;    error = -EMFILE;    if (files->max_fds >= NR_OPEN || nr >= NR_OPEN)        goto out;    nfds = files->max_fds;    write_unlock(&files->file_lock);    /*     * Expand to the max in easy steps, and keep expanding it until     * we have enough for the requested fd array size.     */    do {#if NR_OPEN_DEFAULT < 256        if (nfds < 256)            nfds = 256;        else#endif            if (nfds < (PAGE_SIZE / sizeof(struct file *)))                nfds = PAGE_SIZE / sizeof(struct file *);            else {                nfds = nfds * 2;                if (nfds > NR_OPEN)                    nfds = NR_OPEN;            }    } while (nfds <= nr);    error = -ENOMEM;    new_fds = alloc_fd_array(nfds);    write_lock(&files->file_lock);    if (!new_fds)        goto out;    /* Copy the existing array and install the new pointer */    if (nfds > files->max_fds) {        struct file **old_fds;        int i;        old_fds = xchg(&files->fd, new_fds);        i = xchg(&files->max_fds, nfds);        /* Don't copy/clear the array if we are creating a new           fd array for fork() */        if (i) {            memcpy(new_fds, old_fds, i * sizeof(struct file *));            /* clear the remainder of the array */            memset(&new_fds[i], 0,                   (nfds-i) * sizeof(struct file *));            write_unlock(&files->file_lock);            free_fd_array(old_fds, i);            write_lock(&files->file_lock);        }    } else {        /* Somebody expanded the array while we slept ... */        write_unlock(&files->file_lock);        free_fd_array(new_fds, nfds);        write_lock(&files->file_lock);    }    error = 0;out:    return error;}

asmlinkage long sys_umask(int mask){	mask = xchg(&current->fs->umask, mask & S_IRWXUGO);	return mask;}

voidruntime
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