How to set the process priority in C++

Question

I am working on a program to sort data, and I need to to set the process to priority 31, which I believe is the highest process priority in Windows. I have done some research, but can't figure out how to do it in C++.

in Unix you have nice(int inc) in unistd.h, maybe something similar on Windows? — jcomeau_ictx, Mar 07 '11 at 05:59
Just out of curiosity, why does a program that sorts data need to run at highest priority? — Jeremy Friesner, Dec 22 '11 at 18:59
For future googlers: Setting a really high priority will not significantly improve the throughput of programs like this since it probably uses 99% CPU even on idle priority. A high priority is more useful for reducing latency. — Navin, Apr 20 '13 at 05:17
Indeed, it is only when there is *contention* for the CPU that it even matters. So, please do not set your games to the Highest Priority class. I say that because it can cause a 'priority skew' with system dependencies it may rely on. — dyasta, Jul 26 '17 at 23:15

score 15 · Answer 1 · edited Sep 19 '18 at 11:54

The Windows API call SetPriorityClass allows you to change your process priority, see the example in the MSDN documentation, and use REALTIME_PRIORITY_CLASS to set the highest priority:

SetPriorityClass(GetCurrentProcess(), REALTIME_PRIORITY_CLASS)

Caution: if you are asking for true realtime priority, you are going to get it. This is a nuke. The OS will mercilessly prioritize a realtime priority thread, well above even OS-level input processing, disk-cache flushing, and other high-priority time-critical tasks. You can easily lock up your entire system if your realtime thread(s) drain your CPU capacity. Be cautious when doing this, and unless absolutely necessary, consider using high-priority instead. More information

Michael Haephrati · Answer 2 · 2019-08-15T06:50:32.640

5

The following function will do the job:

void SetProcessPriority(LPWSTR ProcessName, int Priority)
{
    PROCESSENTRY32 proc32;
    HANDLE hSnap;
    if (hSnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0));
    if (hSnap == INVALID_HANDLE_VALUE)
    {

    }
    else
    {
        proc32.dwSize = sizeof(PROCESSENTRY32);
        while ((Process32Next(hSnap, &proc32)) == TRUE)
        {
            if (_wcsicmp(proc32.szExeFile, ProcessName) == 0)
            {
                HANDLE h = OpenProcess(PROCESS_SET_INFORMATION, TRUE, proc32.th32ProcessID);
                SetPriorityClass(h, Priority);
                CloseHandle(h);
            }
        }
        CloseHandle(hSnap);
    }
}

For example, to set the priority of the current process to below normal, use:

SetProcessPriority(GetCurrentProcess(), BELOW_NORMAL_PRIORITY_CLASS)

edited Aug 15 '19 at 06:50

answered Jan 11 '18 at 14:05

Michael Haephrati

2,849
1
27
48

Why are you trying to open the process with `PROCESS_ALL_ACCESS`? Surely, the `SetPriorityClass` API call does not require anything more than `PROCESS_SET_INFORMATION`. – IInspectable Jan 12 '18 at 09:42
What happened to `GetCurrentProcess()`? I believe the OP wants to boost his own program's priority, not someone else's. – Seva Alekseyev Aug 15 '19 at 02:41
@SevaAlekseyev - fixed. Thanks – Michael Haephrati Aug 15 '19 at 06:50

score 1 · Answer 3 · answered Mar 08 '11 at 01:59

1

After (or before) SetPriorityClass, you must set the individual thread priority to achieve the maximum possible. Additionally, another security token is required for realtime priority class, so be sure to grab it (if accessible). SetThreadPriority is the secondary API after SetPriorityClass.

answered Mar 08 '11 at 01:59

dyasta

1,889
15
23

What security token is needed, and how do I get it? – mojo Dec 17 '15 at 15:38
Sorry, you are on your own from here. It is easy stuff. Surely you figured it out, or moved on, by now. – dyasta Jul 26 '17 at 23:16

How to set the process priority in C++

3 Answers3

Linked