Redirecting threaddump to a file

Question

Hi,
We have the following issue.
We are genereating thread dump using the JNI call as below
#include <jni.h>
#include "Test.h"
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
JNIEXPORT void JNICALL JVM_DumpAllStacks(JNIEnv *env, jclass unused);
JNIEXPORT jstring JNICALL Java_MyThread_createThreadDump(JNIEnv *env, jclass clazz)
     jstring str = NULL;
char* pszConsoleOutput = NULL;
char* tmpFile = NULL;
struct stat buf;
int sfildes, tfildes;
int len;
/* Open a tmp file to record thread info */
tmpFile = tmpnam(NULL);
tfildes = open(tmpFile, O_CREAT|O_RDWR, 0666);
if (unlink(tmpFile) == -1)
return NULL;
/* Duplicate a standard file descriptor */
sfildes = dup(1);
/* file descriptor 1 point to tfildes */
dup2(tfildes, 1);
/* Trigger thread dump */
JVM_DumpAllStacks(env, NULL);
/* file descriptor 1 point back to sfildes */
dup2(sfildes, 1);
/* Move the file pointer to the begining */
lseek(tfildes, 0, SEEK_SET);
/* Get the file size */
fstat(tfildes, &buf);
len = buf.st_size;
/* Read the content in tmp file into output buffer */
if (len > 0)
pszConsoleOutput = (char *) malloc(len * sizeof(char));
read(tfildes, pszConsoleOutput, len);
pszConsoleOutput[len] = '\0';
/* Display the thread output in Java Console */
if (pszConsoleOutput != NULL)
str = (*env)->NewStringUTF(env, pszConsoleOutput);
/* Release memory */
free(pszConsoleOutput);
return str;
we are trying to capture it in a temp file, but the dump vanishes.
Can anyone help us in capturing the thread dump generated at the console.

Answer 1

Here's something to get you started...
import java.io.* ;
public class Logger {
    private File logFile ;
    public Logger(File logFile) throws IOException {
        this.logFile = logFile ;
        log("starting log...") ;
    public void log(String msg) throws IOException {
        synchronized (logFile) {
            PrintWriter logWriter = new PrintWriter(new FileWriter(logFile.toString(), true)) ;
            logWriter.println(msg) ;
            logWriter.flush() ;
            logWriter.close() ;
    public void log(String msg, Throwable th) throws IOException  {
        synchronized (logFile) {
            PrintWriter logWriter = new PrintWriter(new FileWriter(logFile.toString(), true)) ;
            logWriter.println(msg) ;
            th.printStackTrace(logWriter) ;      // <<---***
            logWriter.flush() ;
            logWriter.close() ;
}Throwable.printStacktrace() goes to the standard err (System.err) by default incidentally.