MACH_TASK_BASIC_INFO的Swift指针问题

我有点更新了Airspeed Velocity对最新swift语法(Swift 3,beta 6)的回答,但这是我得到的:

func report_memory() {
    var info = mach_task_basic_info()
    let MACH_TASK_BASIC_INFO_COUNT = MemoryLayout<mach_task_basic_info>.stride/MemoryLayout<natural_t>.stride
    var count = mach_msg_type_number_t(MACH_TASK_BASIC_INFO_COUNT)

    let kerr: kern_return_t = withUnsafeMutablePointer(to: &info) {
        $0.withMemoryRebound(to: integer_t.self, capacity: MACH_TASK_BASIC_INFO_COUNT) {
            task_info(mach_task_self_,
                      task_flavor_t(MACH_TASK_BASIC_INFO),
                      $0,
                      &count)
        }
    }

    if kerr == KERN_SUCCESS {
        print("Memory in use (in bytes): \(info.resident_size)")
    }
    else {
        print("Error with task_info(): " +
            (String(cString: mach_error_string(kerr), encoding: String.Encoding.ascii) ?? "unknown error"))
    }
}

希望这很有帮助.

Nate的答案非常好,但您可以通过调整来简化它.

首先,task_basic_info您可以在堆栈上创建结构,而不是分配/取消分配指针,然后使用withUnsafeMutablePointer直接获取指针,您可以传入该指针.

func report_memory() {
    var info = mach_task_basic_info()
    var count = mach_msg_type_number_t(sizeofValue(info))/4

    let kerr: kern_return_t = withUnsafeMutablePointer(&info) {

        task_info(mach_task_self_,
            task_flavor_t(MACH_TASK_BASIC_INFO),
            task_info_t($0),
            &count)

    }

    if kerr == KERN_SUCCESS {
        println("Memory in use (in bytes): \(info.resident_size)")
    }
    else {
        println("Error with task_info(): " +
            (String.fromCString(mach_error_string(kerr)) ?? "unknown error"))
    }
}

与C函数交互时,您不能依赖编译器的错误消息 - 按参数分解参数,按住命令单击,直到您知道正在使用的内容为止.首先,您遇到的类型是:

task_name_t: UInt32

task_flavor_t: UInt32

task_info_t: UnsafeMutablePointer<Int32>

UnsafeMutablePointer<mach_msg_type_number_t>: UnsafeMutablePointer<UInt32>

kern_return_t - Int32

有一个棘手的Swift位以及你的代码中存在的错误.首先,task_info_out参数需要是a UnsafeMutablePointer<UInt32>,但实际上需要指向一个实例mach_task_basic_info.我们可以通过在调用时创建一个UnsafeMutablePointer<mach_task_basic_info>并将其包装在另一个 UnsafeMutablePointer中来解决这个问题- 编译器将使用类型推断来知道我们希望包装指针被子类型化为UInt32.

其次,当你应该调用时,你正在调用sizeof(mach_task_basic_info_t)(指向mach_task_basic_info)sizeinfo(mach_task_basic_info),因此你的字节数太低而无法容纳数据结构.

在进一步的研究中,这有点复杂.原始代码不正确,size应该初始化为常量MACH_TASK_BASIC_INFO_COUNT.不幸的是,这是一个宏,而不是一个简单的常量:

#define MACH_TASK_BASIC_INFO_COUNT (sizeof(mach_task_basic_info_data_t) / sizeof(natural_t)) 

Swift不会导入它们,所以我们需要自己重新定义它们.这是所有这些的工作代码:

// constant
let MACH_TASK_BASIC_INFO_COUNT = (sizeof(mach_task_basic_info_data_t) / sizeof(natural_t))

// prepare parameters
let name   = mach_task_self_
let flavor = task_flavor_t(MACH_TASK_BASIC_INFO)
var size   = mach_msg_type_number_t(MACH_TASK_BASIC_INFO_COUNT)

// allocate pointer to mach_task_basic_info
var infoPointer = UnsafeMutablePointer<mach_task_basic_info>.alloc(1)

// call task_info - note extra UnsafeMutablePointer(...) call
let kerr = task_info(name, flavor, UnsafeMutablePointer(infoPointer), &size)

// get mach_task_basic_info struct out of pointer
let info = infoPointer.move()

// deallocate pointer
infoPointer.dealloc(1)

// check return value for success / failure
if kerr == KERN_SUCCESS {
    println("Memory in use (in bytes): \(info.resident_size)")
} else {
    let errorString = String(CString: mach_error_string(kerr), encoding: NSASCIIStringEncoding)
    println(errorString ?? "Error: couldn't parse error string")
}