Remove char[] allocations from RegistryKey

[stephentoub]

Replace char[] allocations with stackalloc'd memory, or ArrayPool as a fallback if the size is too large.

I also noticed that the handler for REG_EXPAND_SZ was identical to the handler for REG_SZ save for one block, so I just collapsed the two and added an additional condition to that one block.

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Issue Details

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Replace char[] allocations with stackalloc'd memory, or ArrayPool as a fallback if the size is too large.

I also noticed that the handler for REG_EXPAND_SZ was identical to the handler for REG_SZ save for one block, so I just collapsed the two and added an additional condition to that one block.

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-Microsoft.Win32
Milestone:	-

[stephentoub]

I rewrote InternalGetValueCore. It now starts with a stackalloc'd buffer, and if that's large enough, doesn't make any further calls. It also checks the return value of RegQueryValueEx for any calls it makes, and it removes a bunch of duplicated code.

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using Microsoft.Win32;

[MemoryDiagnoser]
public class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private static readonly RegistryKey s_netFramework = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\.NETFramework");
    private static readonly RegistryKey s_hardwareCurrent = Registry.LocalMachine.OpenSubKey(@"System\HardwareConfig\Current");

    [Benchmark] public string RegSz() => (string)s_netFramework.GetValue("InstallRoot");
    [Benchmark] public int RegDword() => (int)s_netFramework.GetValue("Enable64Bit");
    [Benchmark] public string[] RegMultiSz() => (string[])s_hardwareCurrent.GetValue("SystemBiosVersion");
}

Method	Toolchain	Mean	Ratio	Allocated
RegSz	\main\corerun.exe	5.702 us	1.00	200 B
RegSz	\pr\corerun.exe	2.949 us	0.52	96 B
RegDword	\main\corerun.exe	5.495 us	1.00	24 B
RegDword	\pr\corerun.exe	2.903 us	0.53	24 B
RegMultiSz	\main\corerun.exe	5.930 us	1.00	368 B
RegMultiSz	\pr\corerun.exe	3.102 us	0.52	256 B

[jkotas]

Build breaks in CoreLib...

[stephentoub]

Build breaks in CoreLib...

Ah, I'd searched for this file in *.csproj, forgot *.projitems.

[jkotas]

Nice!

[danmoseley]

@stephentoub are you still working on this one?

[stephentoub]

are you still working on this one?

Yes.

[stephentoub]

I believe I finally figured out the issues that were causing failures here; perf keys are special and have undocumented requirements (or at least requirements I couldn't find), like the input buffer has to be zero'd.

@jkotas, could you re-review?

[jkotas]

LGTM