Remove @Synchronized annotation from Rfc3339DateJsonAdapter.

[sangho-block]

Motivation

Rfc3339DateJsonAdapter can convert a nullable Date object to a JSON string and vice versa.

If a system attempts to concurrently serialize or deserialize large objects containing many Date objects or collections of those large objects, there could be contention across threads and delays due to synchronization.

Synchronization evaluation

1. fromJson

fromJson constructs and uses a local Calendar instance and does not use any shared DateFormat, thus it should not need to be synchronized.

2. toJson

toJson calls Date.formatIsoDate extension method, which provides a (mutable) Date object to local Calendar instance.

internal fun Date.formatIsoDate(): String {
  val calendar: Calendar = GregorianCalendar(TIMEZONE_Z, Locale.US)
  calendar.time = this
  // ...
}

The underlying code for calendar.time = this simply gets the Long time value from the Date object which is a thread-safe operation.

  public final void setTime(Date date) {
     Objects.requireNonNull(date, "date must not be null");
     setTimeInMillis(date.getTime());
  }

Therefore, synchronized execution shouldn't be needed for toJson.

Changes

• Remove @Synchronized annotation from fromJson and toJson in Rfc3339DateJsonAdapter to make it usable concurrently.

Outcome

Lower contention across threads & synchronization overhead can improve efficiency and compute resource utilization in multi-threaded environments such as in backend servers.

Benchmark

Setup

• M1 Max MBP
• 100 fixed threads
• 1000 serialization and deserialization tasks
  • Each object with a collection of 100 objects with date property.

Outcome

Benchmark                         Mode  Cnt   Score    Error  Units
BenchmarkDate.synchronized       thrpt    5  10.707  ± 0.052  ops/s   // before
BenchmarkDate.non-synchronized   thrpt    5  77.978  ± 5.109  ops/s   // after

[dreamofabear]

Consider adding a comment explicitly stating that these should NOT be synchronized to avoid accidental future regression.