chia7712 commented on code in PR #22454:
URL: https://github.com/apache/kafka/pull/22454#discussion_r3459952737
##########
server/src/main/java/org/apache/kafka/server/metrics/LinuxIoMetricsCollector.java:
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@@ -79,32 +141,61 @@ public long writeBytes() {
* read_bytes: 0
* write_bytes: 0
* cancelled_write_bytes: 0
+ *
+ * <p>Parses into local variables first, then publishes to the volatile
cached fields only
+ * after parsing succeeds. This prevents lock-free readers from observing
the transient
+ * -1L state during an update. {@code lastUpdateMs} is written last so any
thread observing
+ * the new timestamp via a volatile read also observes all updated cached
fields.
+ *
+ * <p>Caller must hold the monitor of this instance.
*/
private boolean updateValues(long now) {
- synchronized (this) {
- try {
- cachedReadBytes = -1L;
- cachedWriteBytes = -1L;
- List<String> lines = Files.readAllLines(path,
StandardCharsets.UTF_8);
- for (String line : lines) {
- if (line.startsWith(READ_BYTES_PREFIX)) {
- cachedReadBytes =
Long.parseLong(line.substring(READ_BYTES_PREFIX.length()));
- } else if (line.startsWith(WRITE_BYTES_PREFIX)) {
- cachedWriteBytes =
Long.parseLong(line.substring(WRITE_BYTES_PREFIX.length()));
- }
+ long readBytes = -1L;
+ long writeBytes = -1L;
+ long rchar = -1L;
+ long wchar = -1L;
+ long syscr = -1L;
+ long syscw = -1L;
+ long cancelledWriteBytes = -1L;
+ try {
+ List<String> lines = Files.readAllLines(path,
StandardCharsets.UTF_8);
+ for (String line : lines) {
+ if (line.startsWith(READ_BYTES_PREFIX)) {
+ readBytes =
Long.parseLong(line.substring(READ_BYTES_PREFIX.length()));
+ } else if (line.startsWith(WRITE_BYTES_PREFIX)) {
+ writeBytes =
Long.parseLong(line.substring(WRITE_BYTES_PREFIX.length()));
+ } else if (line.startsWith(RCHAR_PREFIX)) {
+ rchar =
Long.parseLong(line.substring(RCHAR_PREFIX.length()));
+ } else if (line.startsWith(WCHAR_PREFIX)) {
+ wchar =
Long.parseLong(line.substring(WCHAR_PREFIX.length()));
+ } else if (line.startsWith(SYSCR_PREFIX)) {
+ syscr =
Long.parseLong(line.substring(SYSCR_PREFIX.length()));
+ } else if (line.startsWith(SYSCW_PREFIX)) {
+ syscw =
Long.parseLong(line.substring(SYSCW_PREFIX.length()));
+ } else if (line.startsWith(CANCELLED_WRITE_BYTES_PREFIX)) {
+ cancelledWriteBytes =
Long.parseLong(line.substring(CANCELLED_WRITE_BYTES_PREFIX.length()));
}
- lastUpdateMs = now;
- return true;
- } catch (Throwable t) {
- LOG.warn("Unable to update IO metrics", t);
- return false;
}
+ } catch (Throwable t) {
+ LOG.warn("Unable to update IO metrics", t);
Review Comment:
Should we update `lastUpdateMs` here to avoid flooding the log?
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