Java JNA 4.3.0 Creates Insane Amout of Garbage When Looking for Process

Question

JNA is making an insane amount of garbage when I'm trying to find a fake process by name.

Here is a screenshot of the allocations (about 100k.sec)

Here is the test case (used 4.3.0 SNAPSHOT of JNA)

import com.sun.jna.Native;
import com.sun.jna.platform.win32.Kernel32;
import com.sun.jna.platform.win32.Tlhelp32;
import com.sun.jna.platform.win32.WinDef;
import com.sun.jna.platform.win32.WinNT;

/**
 * Created by Jonathan on 8/26/2016.
 */
public class Main {

    public static void main(String[] args) {
        while (true)
            openProcess("doesntexist.exe");
    }

    private static final WinDef.DWORD DWORD_ZERO = new WinDef.DWORD(0);
    private static final Tlhelp32.PROCESSENTRY32 entry = new Tlhelp32.PROCESSENTRY32.ByReference();

    private static WinNT.HANDLE openProcess(String processName) {
        WinNT.HANDLE snapshot = Kernel32.INSTANCE.CreateToolhelp32Snapshot(Tlhelp32.TH32CS_SNAPALL, DWORD_ZERO);
        try {
            while (Kernel32.INSTANCE.Process32Next(snapshot, entry)) {
                String fileName = Native.toString(entry.szExeFile);
                if (processName.equals(fileName))
                    return Kernel32.INSTANCE.OpenProcess(WinNT.PROCESS_ALL_ACCESS, true, entry.th32ProcessID.intValue());
            }
        } finally {
            Kernel32.INSTANCE.CloseHandle(snapshot);
        }
        return null;
    }

}

And finally here is the memory snapshot https://dl.dropboxusercontent.com/u/91292881/ShareX/2016/08/JNA%204.3.0.snapshot

How many processes are you creating? Just tracing the code it looks like the while loop creates a `Tlhelp32.PROCESSENTRY32` structure for every one of them. — Daniel Widdis, Aug 29 '16 at 07:11
Also where are you getting 4.3.0? The latest release is 4.2.2. Is this a snapshot build? — Daniel Widdis, Aug 29 '16 at 07:13

score 1 · Accepted Answer · answered Sep 01 '16 at 03:58

I strongly suspect your heap usage is the repeated creation of new String objects inside your loop.

Your code executes the process search (which looks through every process) inside another endless loop so you're effectively executing this line over and over...

String fileName = Native.toString(entry.szExeFile);

Internally, Native.toString(char[] buf) is creating a new String() each time:

public static String toString(char[] buf) {
    int len = buf.length;
    for (int index = 0; index < len; index++) {
        if (buf[index] == '\0') {
            len = index;
            break;
        }
    }

    if (len == 0) {
        return "";
    } else {
        return new String(buf, 0, len);
    }
}

These String objects are used once to test equality and then are tossed on to the heap.

Since the main purpose of creating the String is to test equality, you can probably test equality directly using the underlying char[] array. Convert processName to a char[] and iterate simultaneously over both arrays, testing for character equality up to the length of processName with a null terminator in the next character of entry.szExeFile.

Java JNA 4.3.0 Creates Insane Amout of Garbage When Looking for Process

1 Answers1