jdk/test/hotspot/jtreg/runtime/os/AvailableProcessors.java

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/*
 * @test
 * @bug 6515172 8148766
 * @summary Check that availableProcessors reports the correct value when running in a cpuset on linux
 * @requires os.family == "linux"
 * @requires vm.flagless
 * @modules java.base/jdk.internal.misc
 * @library /test/lib
 * @run driver AvailableProcessors
 */

import jdk.test.lib.process.ProcessTools;
import jdk.test.lib.process.OutputAnalyzer;
import jtreg.SkippedException;

import java.util.ArrayList;
import java.io.File;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class AvailableProcessors {

    static final String SUCCESS_STRING = "Found expected processors: ";

    public static void main(String[] args) throws Exception {
        if (args.length > 0)
            checkProcessors(Integer.parseInt(args[0]));
        else {
            // run ourselves under different cpu configurations
            // using the taskset command
            String taskset;
            final String taskset1 = "/bin/taskset";
            final String taskset2 = "/usr/bin/taskset";
            if (new File(taskset1).exists()) {
                taskset = taskset1;
            } else if (new File(taskset2).exists()) {
                taskset = taskset2;
            } else {
                throw new SkippedException("Could not find taskset command");
            }

            int available = Runtime.getRuntime().availableProcessors();

            if (available == 1) {
                throw new SkippedException("only one processor available");
            }

            // Get the java command we want to execute
            // Enable logging for easier failure diagnosis
            ProcessBuilder master =
                    ProcessTools.createLimitedTestJavaProcessBuilder("-Xlog:os=trace",
                                                                     "AvailableProcessors");

            int[] expected = new int[] { 1, available/2, available-1, available };
            int cpuId = getFirstAllowedCpu();
            if (cpuId == -1) {
                throw new SkippedException("Could not determine allowed CPU cores");
            }

            for (int i : expected) {
                System.out.println("Testing for " + i + " processors ...");
                int max = i - 1 + cpuId;
                ArrayList<String> cmdline = new ArrayList<>(master.command());
                // prepend taskset command
                cmdline.add(0, cpuId + "-" + max);
                cmdline.add(0, "-c");
                cmdline.add(0, taskset);
                // append expected processor count
                cmdline.add(String.valueOf(i));
                ProcessBuilder pb = new ProcessBuilder(cmdline);
                System.out.println("Final command line: " +
                                   ProcessTools.getCommandLine(pb));
                OutputAnalyzer output = ProcessTools.executeProcess(pb);
                output.shouldHaveExitValue(0);
                output.shouldContain(SUCCESS_STRING);
            }
        }
    }

    static void checkProcessors(int expected) {
        int available = Runtime.getRuntime().availableProcessors();
        // available can dynamically drop below expected due to aggressive power management
        // but we should never have more than expected, else taskset is broken
        if (available <= 0 || available > expected)
            throw new Error("Expected " + expected + " processors, but found "
                            + available);
        else
            System.out.println(SUCCESS_STRING + available);
    }

    /**
     * Retrieves the first available CPU core ID allowed for the current process on Linux.
     *
     * @return The first CPU ID in Cpus_allowed_list, or -1 if unavailable.
     */
    static int getFirstAllowedCpu() {
        final String statusFile = "/proc/self/status";
        final String targetKey = "Cpus_allowed_list:";

        try (BufferedReader br = new BufferedReader(new FileReader(statusFile))) {
            String line;
            while ((line = br.readLine()) != null) {
                // Look for the line starting with "Cpus_allowed_list:"
                if (line.startsWith(targetKey)) {
                    // Extract the value part, e.g., "0-15,32-47" or "80,82,84"
                    String listValue = line.substring(targetKey.length()).trim();
                    if (listValue.isEmpty()) return -1;

                    // Get the first segment before any comma (e.g., "0-15" from "0-15,32")
                    String firstSegment = listValue.split(",")[0];

                    // If it is a range (e.g., "80-159"), take the start number
                    if (firstSegment.contains("-")) {
                        return Integer.parseInt(firstSegment.split("-")[0]);
                    } else {
                        // If it is a single ID (e.g., "1"), parse it directly
                        return Integer.parseInt(firstSegment);
                    }
                }
            }
        } catch (IOException | NumberFormatException | ArrayIndexOutOfBoundsException e) {
            throw new RuntimeException("Failed to read or parse " + statusFile, e);
        }
        return -1;
    }
}