pan3793 commented on PR #52665:
URL: https://github.com/apache/spark/pull/52665#issuecomment-3626784001
@mridulm Spark should correctly resolve `JAVA_HOME` env var or fail fast
when launching by `spark-submit` or other shell scripts, but you are right,
it's still possible that the user uses Spark as a library and creates
`SparkContext` from their Java process.
How do you think about code below for Spark 3.5?
```scala
private lazy val jmapCmd: Option[String] = {
def jmapExists(maybeJavaHome: String): Boolean =
Files.exists(Paths.get(maybeJavaHome, "/bin/jmap"))
Option(System.getenv("JAVA_HOME")).filter(jmapExists)
.orElse(Option(System.getProperty("java.home")).filter(jmapExists))
.map(javaHome => javaHome + "/bin/jmap")
}
/** Return a heap dump. Used to capture dumps for the web UI */
def getHeapHistogram(): Array[String] = jmapCmd.map { jmap =>
// From Java 9+, we can use 'ProcessHandle.current().pid()'
val pid = getProcessName().split("@").head
val builder = new ProcessBuilder(jmap, "-histo:live", pid)
val p = builder.start()
val rows = ArrayBuffer.empty[String]
Utils.tryWithResource(new BufferedReader(new
InputStreamReader(p.getInputStream()))) { r =>
var line = ""
while (line != null) {
if (line.nonEmpty) rows += line
line = r.readLine()
}
}
rows.toArray
}.getOrElse {
logWarning("Return empty heap histogram due to jcmd is unavailable.")
Array.empty
}
```
Additionally, I found that `jmap` is still possible to be missing after Java
17, for example,
```
$ docker run -it ubuntu:24.04 bash
# apt update
# apt install openjdk-25-jre-headless
# ll /usr/lib/jvm/java-25-openjdk-arm64/bin/
total 280
drwxr-xr-x 2 root root 4096 Dec 8 12:30 ./
drwxr-xr-x 6 root root 4096 Dec 8 12:30 ../
-rwxr-xr-x 1 root root 67480 Oct 23 09:23 java*
-rwxr-xr-x 1 root root 67504 Oct 23 09:23 jpackage*
-rwxr-xr-x 1 root root 67504 Oct 23 09:23 keytool*
-rwxr-xr-x 1 root root 67512 Oct 23 09:23 rmiregistry*
```
So, maybe we also want a variant method to find `jmap` for the master branch?
```scala
private lazy val jmapCmd: Option[String] = {
def jmapExists(maybeJavaHome: String): Boolean =
Files.exists(Paths.get(maybeJavaHome, "/bin/jmap"))
Option(System.getProperty("java.home")).filter(jmapExists)
.map(javaHome => javaHome + "/bin/jmap")
}
```
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