private void printStackTrace(PrintStreamOrWriter s) {
        // Guard against malicious overrides of Throwable.equals by
        // using a Set with identity equality semantics.
        Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
        dejaVu.add(this);

        synchronized (s.lock()) {
            // Print our stack trace
            s.println(this);
            StackTraceElement[] trace = getOurStackTrace();
            for (StackTraceElement traceElement : trace)
                s.println("\tat " + traceElement);

            // Print suppressed exceptions, if any
            for (Throwable se : getSuppressed())
                se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);

            // Print cause, if any
            Throwable ourCause = getCause();
            if (ourCause != null)
                ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
        }
    }

// File: java/lang/Throwable.java

    public void printStackTrace(PrintStream s) {
        printStackTrace(new WrappedPrintStream(s));
                     // ^ Locks this object.
    }

    private void printStackTrace(PrintStreamOrWriter s) {
        ...
        ...
    }

// File: android/util/Log.java

    public static int printlns(int bufID, int priority, @Nullable String tag, @NonNull String msg,
            @Nullable Throwable tr) {
        ImmediateLogWriter logWriter = new ImmediateLogWriter(bufID, priority, tag);
        // Acceptable buffer size. Get the native buffer size, subtract two zero terminators,
        // and the length of the tag.
        // Note: we implicitly accept possible truncation for Modified-UTF8 differences. It
        //       is too expensive to compute that ahead of time.
        int bufferSize = PreloadHolder.LOGGER_ENTRY_MAX_PAYLOAD    // Base.
                - 2                                                // Two terminators.
                - (tag != null ? tag.length() : 0)                 // Tag length.
                - 32;                                              // Some slack.
        // At least assume you can print *some* characters (tag is not too large).
        bufferSize = Math.max(bufferSize, 100);

        LineBreakBufferedWriter lbbw = new LineBreakBufferedWriter(logWriter, bufferSize);

        lbbw.println(msg);

        if (tr != null) {
            // This is to reduce the amount of log spew that apps do in the non-error
            // condition of the network being unavailable.
            Throwable t = tr;
            while (t != null) {
                if (t instanceof UnknownHostException) {
                    break;
                }
                if (t instanceof DeadSystemException) {
                    lbbw.println("DeadSystemException: The system died; "
                            + "earlier logs will point to the root cause");
                    break;
                }
                t = t.getCause();
            }
            if (t == null) {
                tr.printStackTrace(lbbw);
            }
        }

        lbbw.flush();
          // ^^^ Only flush logs here ^^^

        return logWriter.getWritten();
    }

    private void printStackTrace(PrintStreamOrWriter s) {

        Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
        dejaVu.add(this);

        synchronized (s.lock()) {
            s.println(this);
            StackTraceElement[] trace = getOurStackTrace();
            for (StackTraceElement traceElement : trace)
                s.println("\tat " + traceElement);
               // ^^^ Print message directly to stderr/stdout

            for (Throwable se : getSuppressed())
                se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
                // ^^^ Print message directly to stderr/stdout
            
            Throwable ourCause = getCause();
            if (ourCause != null)
                ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
                      // ^^^ Print message directly to stderr/stdout
        }
    }

synchronized (s.lock()) {
    // …
}

    private static class WrappedPrintStream extends PrintStreamOrWriter {
        private final PrintStream printStream;

        WrappedPrintStream(PrintStream printStream) {
            this.printStream = printStream;
        }

        Object lock() {
            return printStream;
        }

        void println(Object o) {
            printStream.println(o);
        }
    }