Use simple loops to process cgroup files

Author: pejovica

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemController.java

@@ -26,15 +26,12 @@
 package jdk.internal.platform;
 
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.math.BigInteger;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Optional;
 import java.util.function.Function;
-import java.util.stream.Stream;
 
 /**
  * Cgroup version agnostic controller logic
@@ -161,16 +158,18 @@ public static double getDoubleValue(CgroupSubsystemController controller, String
     public static long getLongEntry(CgroupSubsystemController controller, String param, String entryname, long defaultRetval) {
         if (controller == null) return defaultRetval;
 
-        try (Stream<String> lines = CgroupUtil.readFilePrivileged(Paths.get(controller.path(), param))) {
-
-            Optional<String> result = lines.map(line -> line.split(" "))
-                                           .filter(line -> (line.length == 2 &&
-                                                   line[0].equals(entryname)))
-                                           .map(line -> line[1])
-                                           .findFirst();
+        try {
+            long result = defaultRetval;
+            for (String line : CgroupUtil.readAllLinesPrivileged(Paths.get(controller.path(), param))) {
+                String[] tokens = line.split(" ");
+                if (tokens.length == 2 && tokens[0].equals(entryname)) {
+                    result = Long.parseLong(tokens[1]);
+                    break;
+                }
+            }
 
-            return result.isPresent() ? Long.parseLong(result.get()) : defaultRetval;
-        } catch (UncheckedIOException | IOException e) {
+            return result;
+        } catch (IOException e) {
             return defaultRetval;
         }
     }

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java

@@ -26,7 +26,6 @@
 package jdk.internal.platform;
 
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.lang.System.Logger;
 import java.lang.System.Logger.Level;
 import java.nio.file.Path;
@@ -38,7 +37,6 @@
 import java.util.Optional;
 import java.util.Objects;
 import java.util.function.Consumer;
-import java.util.stream.Stream;
 
 import jdk.internal.platform.cgroupv1.CgroupV1Subsystem;
 import jdk.internal.platform.cgroupv2.CgroupV2Subsystem;
@@ -56,7 +54,7 @@ static CgroupMetrics create() {
         Optional<CgroupTypeResult> optResult = null;
         try {
             optResult = determineType("/proc/self/mountinfo", "/proc/cgroups", "/proc/self/cgroup");
-        } catch (IOException | UncheckedIOException e) {
+        } catch (IOException e) {
             return null;
         }
         return create(optResult);
@@ -173,16 +171,15 @@ public static Optional<CgroupTypeResult> determineType(String mountInfo,
         // See:
         //   setCgroupV1Path() for the action run for cgroups v1 systems
         //   setCgroupV2Path() for the action run for cgroups v2 systems
-        try (Stream<String> selfCgroupLines =
-             CgroupUtil.readFilePrivileged(Paths.get(selfCgroup))) {
-            Consumer<String[]> action = (tokens -> setCgroupV1Path(infos, tokens));
-            if (isCgroupsV2) {
-                action = (tokens -> setCgroupV2Path(infos, tokens));
-            }
+        Consumer<String[]> action = (tokens -> setCgroupV1Path(infos, tokens));
+        if (isCgroupsV2) {
+            action = (tokens -> setCgroupV2Path(infos, tokens));
+        }
+        for (String line : CgroupUtil.readAllLinesPrivileged(Paths.get(selfCgroup))) {
             // The limit value of 3 is because /proc/self/cgroup contains three
             // colon-separated tokens per line. The last token, cgroup path, might
             // contain a ':'.
-            selfCgroupLines.map(line -> line.split(":", 3)).forEach(action);
+            action.accept(line.split(":", 3));
         }
 
         CgroupTypeResult result = new CgroupTypeResult(isCgroupsV2,

src/java.base/linux/classes/jdk/internal/platform/CgroupUtil.java

@@ -28,33 +28,17 @@
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.nio.charset.StandardCharsets;
-import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.security.AccessController;
 import java.security.PrivilegedActionException;
 import java.security.PrivilegedExceptionAction;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.stream.Stream;
 
 public final class CgroupUtil {
 
-    @SuppressWarnings("removal")
-    public static Stream<String> readFilePrivileged(Path path) throws IOException {
-        try {
-            PrivilegedExceptionAction<Stream<String>> pea = () -> Files.lines(path);
-            return AccessController.doPrivileged(pea);
-        } catch (PrivilegedActionException e) {
-            unwrapIOExceptionAndRethrow(e);
-            throw new InternalError(e.getCause());
-        } catch (UncheckedIOException e) {
-            throw e.getCause();
-        }
-    }
-
     static void unwrapIOExceptionAndRethrow(PrivilegedActionException pae) throws IOException {
         Throwable x = pae.getCause();
         if (x instanceof IOException)

src/java.base/linux/classes/jdk/internal/platform/cgroupv2/CgroupV2Subsystem.java

@@ -26,11 +26,9 @@
 package jdk.internal.platform.cgroupv2;
 
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.nio.file.Paths;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
-import java.util.stream.Collectors;
 
 import jdk.internal.platform.CgroupInfo;
 import jdk.internal.platform.CgroupSubsystem;
@@ -329,10 +327,12 @@ public long getBlkIOServiced() {
 
     private long sumTokensIOStat(Function<String, Long> mapFunc) {
         try {
-            return CgroupUtil.readFilePrivileged(Paths.get(unified.path(), "io.stat"))
-                                .map(mapFunc)
-                                .collect(Collectors.summingLong(e -> e));
-        } catch (UncheckedIOException | IOException e) {
+            long sum = 0L;
+            for (String line : CgroupUtil.readAllLinesPrivileged(Paths.get(unified.path(), "io.stat"))) {
+                sum += mapFunc.apply(line);
+            }
+            return sum;
+        } catch (IOException e) {
             return CgroupSubsystem.LONG_RETVAL_UNLIMITED;
         }
     }