Tencent/matrix · error · ParseException

ProcStatReader error

Error message

ProcStatReader error: ${e.getClass().getName()}, ${e.getMessage()}

What it means

ProcStatUtil.parse wraps its BufferedReader-based /proc stat parsing; any unexpected Exception (IO error, NumberFormatException, index problems) is converted to a ParseException prefixed 'ProcStatReader error:' with the exception class and message, while genuine ParseExceptions are rethrown untouched. It tells you the stat file read itself failed, not that a field was malformed.

Solutions

Read the wrapped class name: IOException means the stat file vanished/unreadable — treat as a transient miss and re-sample.
If it's a NumberFormatException, inspect the stat content for kernel format differences.
Catch ParseException at the call site and continue monitoring rather than disabling the collector.
Verify the target process still exists (check /proc/<pid> before reading) and that the app has /proc read permission (not blocked by hidepid or SELinux).

Example fix

// before
ProcStat stat = ProcStatUtil.parse(reader);
// after
ProcStat stat = null;
try {
    stat = ProcStatUtil.parse(reader);
} catch (ParseException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("ProcStatReader error")) {
        MatrixLog.w(TAG, "stat read failed, will retry: " + e.getMessage());
    }
}

Defensive patterns

Strategy: try-catch

Validate before calling

File f = new File("/proc/" + pid + "/stat");
if (!f.exists() || !f.canRead()) return null;

Type guard

static boolean canReadStat(int pid) {
    File f = new File("/proc/" + pid + "/stat");
    return f.exists() && f.canRead();
}

Try / catch

try {
    stat = ProcStatUtil.parse(reader);
} catch (ParseException e) {
    if (e.getMessage() != null && e.getMessage().contains("ProcStatReader error")) {
        Log.w(TAG, "stat read IO failure, will re-sample: " + e.getMessage());
    }
    stat = null;
}

Prevention

Check /proc/<pid>/stat exists and is readable before parsing (hidepid/SELinux can block it).
Expect IOException when a process exits between open and read — retry the sample.
Don't disable monitoring on a single wrapped failure; count failures and degrade after a threshold.
On failing devices verify kernel /proc stat format.

When it happens

Trigger: Calling ProcStatUtil.parse when the underlying reader throws — /proc/<pid>/stat disappeared mid-read (IOException, process exited), stream closed, or a runtime exception (e.g. NumberFormatException) occurs inside readJiffy/readInt helpers.

Common situations: Device under heavy process churn (parent reaped the process between open and read); restricted /proc access on some OEMs; low-level IO errors from /proc filesystem.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of Tencent/matrix@3b8293bd65 (2026-09-08). Data as JSON: /api/errors/19fed8befcfe336e. Report an issue: GitHub.

Appendix: source

Thrown at matrix/matrix-android/matrix-battery-canary/src/main/java/com/tencent/matrix/batterycanary/utils/ProcStatUtil.java:380

                int index = 0;
                while (index < PROC_USER_TIME_FIELD - 2) {
                    reader.skipSpaces();
                    index++;
                }

                ProcStat stat = new ProcStat();
                stat.comm = String.valueOf(comm);
                stat.stat = String.valueOf(state);
                stat.utime = readJiffy(reader);
                stat.stime = readJiffy(reader);
                stat.cutime = readJiffy(reader);
                stat.cstime = readJiffy(reader);
                return stat;
            } catch (Exception e) {
                if (e instanceof ParseException) {
                    throw e;
                } else {
                    throw new ParseException("ProcStatReader error: " + e.getClass().getName() + ", " + e.getMessage());
                }
            } finally {
                try {
                    reader.close();
                } catch (Exception ignored) {
                }
            }
        }

        private static long readJiffy(ProcStatReader reader) {
            long jiffies = reader.readNumber();
            reader.skipSpaces();
            return jiffies;
        }
    }

    @SuppressWarnings("SpellCheckingInspection")
    public static class ProcStat {

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