GH-36816: [C#] Reduce allocations (#36817)

### What changes are included in this PR?

A small refactoring to make a small improvement in memory utilization.

### Are these changes tested?

Existing test coverage should be sufficient.

* Closes: #36816

Authored-by: Curt Hagenlocher <curt@hagenlocher.org>
Signed-off-by: David Li <li.davidm96@gmail.com>

csharp/src/Apache.Arrow/Arrays/Time32Array.cs

@@ -46,7 +46,7 @@ public Builder()
  : this(Time32Type.Default) { }
 
  public Builder(TimeUnit unit)
- : this(new Time32Type(unit)) { }
+ : this((Time32Type)TimeType.FromTimeUnit(unit)) { }
 
  /// <summary>
  /// Construct a new instance of the <see cref="Builder"/> class.

csharp/src/Apache.Arrow/Arrays/Time64Array.cs

@@ -49,7 +49,7 @@ public Builder()
  : this(Time64Type.Default) { }
 
  public Builder(TimeUnit unit)
- : this(new Time64Type(unit)) { }
+ : this((Time64Type)TimeType.FromTimeUnit(unit)) { }
 
  /// <summary>
  /// Construct a new instance of the <see cref="Builder"/> class.

csharp/src/Apache.Arrow/C/CArrowArrayStreamExporter.cs

@@ -61,9 +61,9 @@ public static unsafe void ExportArrayStream(IArrowArrayStream arrayStream, CArro
  {
  throw new ArgumentNullException(nameof(arrayStream));
  }
- if (arrayStream == null)
+ if (cArrayStream == null)
  {
- throw new ArgumentNullException(nameof(arrayStream));
+ throw new ArgumentNullException(nameof(cArrayStream));
  }
 
  cArrayStream->private_data = ExportedArrayStream.Export(arrayStream);

csharp/src/Apache.Arrow/C/CArrowSchemaImporter.cs

@@ -268,14 +268,14 @@ public ArrowType GetAsType()
  // Date and time
  "tdD" => Date32Type.Default,
  "tdm" => Date64Type.Default,
- "tts" => new Time32Type(TimeUnit.Second),
- "ttm" => new Time32Type(TimeUnit.Millisecond),
- "ttu" => new Time64Type(TimeUnit.Microsecond),
- "ttn" => new Time64Type(TimeUnit.Nanosecond),
+ "tts" => TimeType.Second,
+ "ttm" => TimeType.Millisecond,
+ "ttu" => TimeType.Microsecond,
+ "ttn" => TimeType.Nanosecond,
  // TODO: duration not yet implemented
- "tiM" => new IntervalType(IntervalUnit.YearMonth),
- "tiD" => new IntervalType(IntervalUnit.DayTime),
- //"tin" => new IntervalType(IntervalUnit.MonthDayNanosecond), // Not yet implemented
+ "tiM" => IntervalType.YearMonth,
+ "tiD" => IntervalType.DayTime,
+ //"tin" => IntervalType.MonthDayNanosecond, // Not yet implemented
  _ => throw new NotSupportedException("Data type is not yet supported in import.")
  };
  }

csharp/src/Apache.Arrow/Ipc/MessageSerializer.cs

@@ -165,9 +165,9 @@ private static Types.IArrowType GetFieldArrowType(Flatbuf.Field field, Field[] c
  switch (timeMeta.BitWidth)
  {
  case 32:
- return new Types.Time32Type(timeMeta.Unit.ToArrow());
+ return (Time32Type)TimeType.FromTimeUnit(timeMeta.Unit.ToArrow());
  case 64:
- return new Types.Time64Type(timeMeta.Unit.ToArrow());
+ return (Time64Type)TimeType.FromTimeUnit(timeMeta.Unit.ToArrow());
  default:
  throw new InvalidDataException("Unsupported time bit width");
  }
@@ -178,7 +178,7 @@ private static Types.IArrowType GetFieldArrowType(Flatbuf.Field field, Field[] c
  return new Types.TimestampType(unit, timezone);
  case Flatbuf.Type.Interval:
  Flatbuf.Interval intervalMetadata = field.Type<Flatbuf.Interval>().Value;
- return new Types.IntervalType(intervalMetadata.Unit.ToArrow());
+ return Types.IntervalType.FromIntervalUnit(intervalMetadata.Unit.ToArrow());
  case Flatbuf.Type.Utf8:
  return Types.StringType.Default;
  case Flatbuf.Type.FixedSizeBinary:

csharp/src/Apache.Arrow/Types/IntervalUnit.cs

@@ -19,11 +19,15 @@ namespace Apache.Arrow.Types
  public enum IntervalUnit
  {
  YearMonth = 0,
- DayTime = 1
+ DayTime = 1,
  }
 
  public sealed class IntervalType : FixedWidthType
  {
+ public static readonly IntervalType YearMonth = new IntervalType(IntervalUnit.YearMonth);
+ public static readonly IntervalType DayTime = new IntervalType(IntervalUnit.DayTime);
+ private static readonly IntervalType[] _types = new IntervalType[] { YearMonth, DayTime };
+
  public override ArrowTypeId TypeId => ArrowTypeId.Interval;
  public override string Name => "date";
  public override int BitWidth => 64;
@@ -36,5 +40,10 @@ public IntervalType(IntervalUnit unit = IntervalUnit.YearMonth)
  }
 
  public override void Accept(IArrowTypeVisitor visitor) => Accept(this, visitor);
+
+ public static IntervalType FromIntervalUnit(IntervalUnit unit)
+ {
+ return _types[(int)unit];
+ }
  }
 }

csharp/src/Apache.Arrow/Types/Time32Type.cs

@@ -18,7 +18,7 @@ namespace Apache.Arrow.Types
 {
  public sealed class Time32Type : TimeType
  {
- public static readonly Time32Type Default = new Time32Type();
+ public static readonly Time32Type Default = Millisecond;
 
  public override ArrowTypeId TypeId => ArrowTypeId.Time32;
  public override string Name => "time32";

csharp/src/Apache.Arrow/Types/Time64Type.cs

@@ -18,7 +18,7 @@ namespace Apache.Arrow.Types
 {
  public sealed class Time64Type : TimeType
  {
- public static readonly Time64Type Default = new Time64Type();
+ public static readonly Time64Type Default = Nanosecond;
 
  public override ArrowTypeId TypeId => ArrowTypeId.Time64;
  public override string Name => "time64";

csharp/src/Apache.Arrow/Types/TimeType.cs

@@ -26,11 +26,22 @@ public enum TimeUnit
 
  public abstract class TimeType: FixedWidthType
  {
+ public static readonly Time32Type Second = new Time32Type(TimeUnit.Second);
+ public static readonly Time32Type Millisecond = new Time32Type(TimeUnit.Millisecond);
+ public static readonly Time64Type Microsecond = new Time64Type(TimeUnit.Microsecond);
+ public static readonly Time64Type Nanosecond = new Time64Type(TimeUnit.Nanosecond);
+ private static readonly TimeType[] _types = new TimeType[] { Second, Millisecond, Microsecond, Nanosecond };
+
  public TimeUnit Unit { get; }
 
  protected TimeType(TimeUnit unit)
  {
  Unit = unit;
  }
+
+ public static TimeType FromTimeUnit(TimeUnit unit)
+ {
+ return _types[(int)unit];
+ }
  }
 }