winapi - WinAPI OpenQuery产生错误

Question

我正在使用winapi-rs crate并尝试获取cpu的使用率，但是我什至无法做到这一点。
PdhCollectQueryData转换为十六进制时将返回“-2147481643”，然后错误代码为“0x800007D5(PDH_NO_DATA)没有要返回的数据。”这是我面临的问题。
有人可以帮助确定我做错了什么导致“x800007D5(PDH_NO_DATA)没有数据返回”吗？我可以在C++(下面提供的代码)中使它工作，但是当尝试将其转换为Rust代码时，一切都不会很好。

use wmi::{COMLibrary, Variant, WMIConnection};
use std::{collections::HashMap, ptr::null};
use winapi::{ctypes::{c_char, c_void},um::{pdh::*, winnt::{LPCSTR}}};

#[cfg(windows)]
fn main() -> Result<(), Box<dyn std::error::Error>>  {

    const CPU_TIME: LPCSTR = "\\Processor(_Total)\\% Processor Time".as_ptr() as *const i8;

    unsafe  
    {
        //cpuQuery
        let mut hquery: PDH_HQUERY = std::ptr::null_mut();
        let hquery_address: *mut PDH_HQUERY = &mut hquery as *mut *mut _ as *mut *mut c_void;

        //cpuCounter
        let mut hcounter: PDH_HCOUNTER = std::ptr::null_mut();
        let hcounter_address: *mut PDH_HCOUNTER = &mut hcounter as *mut *mut _ as *mut *mut c_void;

        //open query
        PdhOpenQueryA(null(), 0, hquery_address);

        PdhAddCounterA(hquery, CPU_TIME, 0, hcounter_address);
        
        PdhCollectQueryData(hquery);

    }
    Ok(())
}

如果我打印出这些值，则在程序完成后返回的一些值的示例:

hquery: 0x2541b495e00
hquery_address: 0xce3dafef00
PdhOpenQueryA: 0
PdhCollectQueryData -2147481643

可用的C++代码(摘自另一个Stack Overflow答案，在我运行它时可以正常工作)

#include <TCHAR.h>
#include <pdh.h>
#include <windows.h>
#include <stdio.h>
#include <iostream>
#include <chrono>
#include <thread>  

#pragma comment(lib, "pdh.lib")
using namespace std;

static PDH_HQUERY cpuQuery;
static PDH_HCOUNTER cpuTotal = NULL;
int _tmain(int argc, _TCHAR* argv[])
{
    PdhOpenQuery(NULL, NULL, &cpuQuery);
    PdhAddCounter(cpuQuery, L"\\Processor(_Total)\\% Processor Time", NULL, &cpuTotal);
    PDH_FMT_COUNTERVALUE counterVal;

    PdhCollectQueryData(cpuQuery);
    this_thread::sleep_for(chrono::milliseconds(1000));
    PdhCollectQueryData(cpuQuery);
    PdhGetFormattedCounterValue(cpuTotal, PDH_FMT_DOUBLE, NULL, &counterVal);
    cout << counterVal.doubleValue << "\n";

    getchar();
}

因此，当C++代码正在运行时，计数器就在那儿。对于查询收集的rust代码，我做错了什么，导致其无法正常工作并产生“x800007D5(PDH_NO_DATA)没有要返回的数据”。

Answer 1

这是使用 winapi crate将C++示例转换为Rust的字面意思。
正如IInspectable在评论中所说，您需要添加一些错误处理，在这种情况下，我添加了一些assert_eq!。

use std::ptr;
// winapi = { version = "0.3.9", features = ["pdh", "winerror"] }
use winapi::{ctypes::c_char, shared::winerror::ERROR_SUCCESS, um::pdh::*};

fn main() {
    unsafe {
        let mut cpu_query: PDH_HQUERY = ptr::null_mut();
        let mut cpu_total: PDH_HCOUNTER = ptr::null_mut();

        let err = PdhOpenQueryA(ptr::null(), 0, &mut cpu_query);
        assert_eq!(err, ERROR_SUCCESS as i32);

        let err = PdhAddCounterA(
            cpu_query,
            b"\\Processor(_Total)\\% Processor Time\0".as_ptr() as *const c_char,
            0,
            &mut cpu_total,
        );
        assert_eq!(err, ERROR_SUCCESS as i32);

        let mut counter_val: PDH_FMT_COUNTERVALUE = std::mem::zeroed();
        let err = PdhCollectQueryData(cpu_query);
        assert_eq!(err, ERROR_SUCCESS as i32);

        std::thread::sleep(std::time::Duration::from_millis(1000));

        let err = PdhCollectQueryData(cpu_query);
        assert_eq!(err, ERROR_SUCCESS as i32);

        let err = PdhGetFormattedCounterValue(
            cpu_total,
            PDH_FMT_DOUBLE,
            ptr::null_mut(),
            &mut counter_val,
        );
        assert_eq!(err, ERROR_SUCCESS as i32);

        println!("{:?}", counter_val.u.doubleValue());
    }
}