StringPool

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Introduction

• A high-performance string pooling library based on .NET9's ArrayPool design, optimized for reusing string instances.
• Reduces memory allocations and GC pressure by efficiently managing string lifetimes in performance-sensitive scenarios.

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Features

• ✅ GC Optimization: Minimizes string allocations by reusing pooled instances.
• ✅ Thread-Safe: Supports concurrent operations for multithreaded applications.
• ✅ Lightweight: Low-overhead design with minimal runtime impact.
• ✅ Seamless Integration: Simple API to replace ad-hoc string caching or frequent allocations.

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Why?

• Frequent short-lived string allocations can degrade performance in high-throughput applications.
• Existing solutions like ArrayPool or manual caching lack dedicated support for string pooling.
• StringPool provides a standardized, efficient way to manage reusable strings without GC overhead.

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How to use?

StringPool

• public string Rent(int minimumLength)

  • Rent a string with at least the specified length from the pool.

• public void Return(string array, bool clearArray = true)

  • Return a string to the pool,
  • when clearArray is true (default), the string will be zeroed.

• public string Rent(ReadOnlySpan<char> buffer)

  • Rent a string with at least the specified buffer's length from the pool,
  • and copies the content from the buffer.

UnsafeString

• public bool SetText(ReadOnlySpan<char> buffer)

  • Rents a new internal buffer if the current buffer is null;

  • or resizes the internal buffer if the current buffer's capacity is insufficient.

  • Then copies characters from the provided ReadOnlySpan<char> buffer into the internal buffer,

  • returns true if a new buffer was rented,

  • returns false if no new buffer was rented.

    You can use public static implicit operator string?(UnsafeString? @string) to convert an UnsafeString to a string,

  • the string's Length will be equal to buffer.Length.

• public void Dispose()

  • Resets the internal string and returns it to the pool,
  • then sets the internal string to null.

Customization

• You can use:

  • public static unsafe void Custom(Func<double> getMemoryPressure)

  • public static unsafe void Custom(nint getMemoryPressure)

  • public static unsafe void Custom(delegate* managed<double> getMemoryPressure)

  to customize how StringPool determines memory pressure for its automatic Trim() behavior.

  • < 0.7 -> low
  • [0.7, 0.9) -> medium
  • >= 0.9 -> high

• You can use:

  • public static void Configure(int DOTNET_SYSTEM_BUFFERS_SHAREDSTRINGPOOL_MAXSTRINGSPERPARTITION = 256, int DOTNET_SYSTEM_BUFFERS_SHAREDSTRINGPOOL_MAXPARTITIONCOUNT = int.MaxValue)

  to pre-configure the StringPool.Shared parameters before initialization.

  • DOTNET_SYSTEM_BUFFERS_SHAREDSTRINGPOOL_MAXSTRINGSPERPARTITION: Maximum strings per partition (default: 256)
  • DOTNET_SYSTEM_BUFFERS_SHAREDSTRINGPOOL_MAXPARTITIONCOUNT: Maximum partition count (default: int.MaxValue, clamped to Environment.ProcessorCount)

  ⚠️ Has no effect after StringPool.Shared is initialized.

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Note

⚠️ The actual length of the string rented from StringPool's Rent may not match the requested length.

• If you need the rented string’s actual length to equal the requested length,
• use UnsafeString's public bool SetText(ReadOnlySpan<char> buffer),
• and be sure to call UnsafeString's public void Dispose().

⚠️ The string converted from UnsafeString:

• Does not guarantee the same lifetime or content consistency as the UnsafeString itself.
• The safest practice is to update all strings converted from UnsafeString every time you update the UnsafeString.