Read hsperfdata for Java PIDs if jvmstat is unavailable (#8792)

* Read hsperfdata for Java PIDs if jvmstat is unavailable

* Add equivalent to JDK os::get_temp_directory() for clean-room jvmstat impl.

* Add a comment documenting how JVM processes are enumerated

Co-authored-by: Jaroslav Bachorik <[email protected]>

* Remove unnecessary defensive path separator

Co-authored-by: Brice Dutheil <[email protected]>

* Spotless

---------

Co-authored-by: Jaroslav Bachorik <[email protected]>
Co-authored-by: Brice Dutheil <[email protected]>

Author: 3 people

internal-api/src/main/java/datadog/trace/util/PidHelper.java

@@ -8,11 +8,16 @@
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.lang.management.ManagementFactory;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.Collections;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -64,12 +69,48 @@ private static String findPid() {
     return pid;
   }
 
+  private static String getOSTempDir() {
+    // See
+    // https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppatha#remarks
+    // and
+    // the JDK OS-specific implementations of os::get_temp_directory(), i.e.
+    // https://github.com/openjdk/jdk/blob/f50bd0d9ec65a6b9596805d0131aaefc1bb913f3/src/hotspot/os/bsd/os_bsd.cpp#L886-L904
+    if (Platform.isLinux()) {
+      return "/tmp/";
+    } else if (Platform.isWindows()) {
+      return Stream.of(System.getenv("TMP"), System.getenv("TEMP"), System.getenv("USERPROFILE"))
+          .filter(String::isEmpty)
+          .findFirst()
+          .orElse("C:\\Windows");
+    } else if (Platform.isMac()) {
+      return System.getenv("TMPDIR");
+    } else {
+      return System.getProperty("java.io.tmpdir");
+    }
+  }
+
   public static Set<String> getJavaPids() {
     // Attempt to use jvmstat directly, fall through to jps process fork strategy
     Set<String> directlyObtainedPids = JPSUtils.getVMPids();
     if (directlyObtainedPids != null) {
       return directlyObtainedPids;
     }
+
+    // Some JDKs don't have jvmstat available as a module, attempt to read from the hsperfdata
+    // directory instead
+    try (Stream<Path> stream =
+        // Emulating the hotspot way to enumerate the JVM processes using the perfdata file
+        // https://github.com/openjdk/jdk/blob/d7cb933b89839b692f5562aeeb92076cd25a99f6/src/hotspot/share/runtime/perfMemory.cpp#L244
+        Files.list(Paths.get(getOSTempDir(), "hsperfdata_" + System.getProperty("user.name")))) {
+      return stream
+          .filter(file -> !Files.isDirectory(file))
+          .map(Path::getFileName)
+          .map(Path::toString)
+          .collect(Collectors.toSet());
+    } catch (IOException e) {
+      log.debug("Unable to obtain Java PIDs via hsperfdata", e);
+    }
+
     // there is no supported Java API to achieve this
     // one could use sun.jvmstat.monitor.MonitoredHost but it is an internal API and can go away at
     // any time -