Getting information about process in Swift

Question

I am trying to get some data about a process in Swift. I am using this code as a starting point:

pid_t pid = 10000;
rusage_info_current rusage;
if (proc_pid_rusage(pid, RUSAGE_INFO_CURRENT, (void **)&rusage) == 0)
{
    cout << rusage.ri_diskio_bytesread << endl;
    cout << rusage.ri_diskio_byteswritten << endl;
}

taken from Per Process disk read/write statistics in Mac OS X.

However, I have trouble converting the code above to Swift:

var usage = rusage_info_v3()     
if proc_pid_rusage(100, RUSAGE_INFO_CURRENT, &usage) == 0
{
    Swift.print("Success")
}

The function prod_pid_rusage expects a parameter of type rusage_info_t?, but I can not instantiate an instance of that type. Is it possible to use the function in Swift?

Regards, Sascha

instead of allocating it on the stack, are you able to allocate one on the heap (e.g. ` var usage = UnsafeMutablePointer.allocate(capacity: 1)`) — Scott Thompson, May 09 '17 at 16:28
No, unfortunately I can not: "Cannot pass immutable value of type 'rusage_info_t?' as inout argument" — inexcitus, May 09 '17 at 16:30

Martin R · Accepted Answer · 2017-05-09T19:11:23.703

As in C you have to take the address of a rusage_info_current variable and cast it to the type expected by proc_pid_rusage(). In Swift this is done using withUnsafeMutablePointer() and withMemoryRebound():

let pid = getpid()
var usage = rusage_info_current()

let result = withUnsafeMutablePointer(to: &usage) {
    $0.withMemoryRebound(to: rusage_info_t?.self, capacity: 1) {
        proc_pid_rusage(pid, RUSAGE_INFO_CURRENT, $0)
    }
}
if result == 0 {
    print(usage.ri_diskio_bytesread)
    // ...
}

You have to add

#include <libproc.h>

to the bridging header file to make it compile.

Getting information about process in Swift

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