go - GoLang/CGO : Problems calling Mach API host_statistics() from Go

我使用以下C代码片段来获取OS X上的CPU负载:

    #include <mach/message.h>
    #include <mach/mach_host.h>
    #include <mach/host_info.h>

    [...]

    mach_msg_type_number_t  count = HOST_CPU_LOAD_INFO_COUNT;
    kern_return_t error;
    host_cpu_load_info_data_t r_load;

    mach_port_t host_port = mach_host_self();
    error = host_statistics(host_port, HOST_CPU_LOAD_INFO, (host_info_t)&r_load, &count);

阅读cgo教程后，我尝试将这段代码移植到Go上。产生的代码如下所示:

package main

/*
#include <stdlib.h>
#include <mach/message.h>
#include <mach/mach_host.h>
#include <mach/host_info.h>
*/
import "C"

func main() {
    var err C.kern_return_t
    var host_info_out C.host_info_t
    var host_port C.mach_port_t = C.mach_host_self()

    count := C.mach_msg_type_number_t(C.HOST_CPU_LOAD_INFO_COUNT)

    err = C.host_statistics(C.host_t(host_port), C.HOST_CPU_LOAD_INFO, &host_info_out, &count)
}

但是，当我尝试构建代码时，最终出现以下错误消息

go build cputimes.go
# command-line-arguments
cputimes.go:33: cannot use &host_info_out (type *_Ctype_host_info_t) as type *_Ctype_integer_t in function argument

我不理解为什么cgo提示这种类型。在mach header 中将host_statistics()的签名定义为:

 kern_return_t host_statistics
 (
      host_t host_priv,
      host_flavor_t flavor,
      host_info_t host_info_out,
      mach_msg_type_number_t *host_info_outCnt
 );

最佳答案

函数原型(prototype)说，在示例程序中传递指向host_statistics变量的指针时，host_info_t的第三个参数是host_info_t变量。

查看 mach/host_info.h header file，我们可以看到host_info_t是指针类型:

typedef integer_t   *host_info_t;       /* varying array of int. */

这就解释了为什么收到有关integer_t类型不匹配的错误消息的原因。

在处理该参数时，您的Go代码看起来实际上并不等同于C代码。您可能想要这样的东西:

...
var r_load C.host_cpu_load_info_data_t
...
err = C.host_statistics(C.host_t(host_port), C.HOST_CPU_LOAD_INFO, C.host_info_t(unsafe.Pointer(&r_load)), &count)
...

(您需要使用unsafe包在不兼容的指针类型之间进行转换)。

关于go - GoLang/CGO : Problems calling Mach API host_statistics() from Go，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/19123059/