[BUG] cygpath calls on Windows seems to slown down agent a lot

Hey, there is my research results with Opus on this issue.

# Claude Code Windows Performance Issue - Detailed Report ## Summary Claude Code on Windows experiences 5-30 second delays due to MSYS2 runtime initialization when calling bash.exe for path conversion operations. ## Environment - OS: Windows (domain-joined corporate machine) - Git Installation: C:\Program Files\Git (Git for Windows / MSYS2-based) - Shell: PowerShell - No issues on WSL - only native Windows ## Root Cause Claude Code calls bash.exe to run cygpath: `` "C:\Program Files\Git\bin\bash.exe" -c "cygpath -u 'C:\path\to\file'" ` The bash.exe (MSYS2 binary) has severe cold-start overhead: `powershell PS> Measure-Command { & "C:\Program Files\Git\bin\bash.exe" -c "echo hello" } TotalSeconds : 28.4885132 ` **28 seconds** just to echo "hello". ## Why MSYS2 is Slow on Domain Machines Every MSYS2 executable initialization: 1. Loads msys-2.0.dll (POSIX emulation layer) 2. Initializes shared "cygheap" memory segment 3. **Queries Active Directory for user/group info** ← Main bottleneck 4. Sets up signal handlers, terminal info, mount tables 5. Then finally runs the actual command On domain-joined machines, step 3 can take 10-30 seconds, especially: - First call after cache expires - Concurrent calls (mutex locking on shared cygheap) - VPN/network latency to domain controllers ## Observed Behavior | Scenario | Time | |----------|------| | First cygpath call | ~29 seconds | | Subsequent calls (cached) | ~66ms | | After ~10-20 calls | Slow again (cache expires) | | Two concurrent calls | Both slow (locking) | | bash.exe -c "echo hello" | ~28 seconds | ## The Real Issue cygpath is just string manipulation - it doesn't need bash or MSYS2 runtime. The current call chain: ` Claude Code → bash.exe (MSYS2) → cygpath.exe (MSYS2) → return path ↑ ↑ 28s overhead (was 29s, now fixed) ` ## Recommended Fix ### Option 1: Call cygpath directly (quick fix) Instead of: ` bash.exe -c "cygpath -u '/path'" ` Call directly: ` cygpath.exe -u "/path" ` This eliminates bash.exe overhead but cygpath.exe still has MSYS2 startup cost. ### Option 2: Native path conversion (proper fix) Implement path conversion in Node.js natively: `javascript function unixToWindows(p) { // /c/Users/foo → C:\Users\foo return p.replace(/^\/([a-zA-Z])\//, '$1:\\').replace(/\//g, '\\'); } function windowsToUnix(p) { // C:\Users\foo → /c/Users/foo return p.replace(/^([a-zA-Z]):/, '/$1').replace(/\\/g, '/').toLowerCase(); } ` No shell spawning needed. Instant. ### Option 3: Cache results If shell calls are necessary, cache the results. Path mappings don't change during a session. ### Option 4: Use PowerShell instead of bash PowerShell is native Windows and has no MSYS2 overhead: `powershell # Much faster than bash.exe powershell -Command "echo hello" # ~200ms vs 28s ` ## Workaround Applied We created a Go-based cygpath.exe replacement without MSYS2 dependencies: - **Before**: 29 seconds (cold), 66ms (warm) - **After**: 25ms (always) However, this doesn't help because Claude Code wraps cygpath in bash.exe, which is still slow. ## Files - main.go - Fast cygpath replacement source - cygpath.exe - Compiled binary (installed to Git\usr\bin) - README.md - Installation/recovery instructions ## Test Commands `powershell # Test bash overhead Measure-Command { & "C:\Program Files\Git\bin\bash.exe" -c "echo hello" } # Test cygpath directly Measure-Command { & "C:\Program Files\Git\usr\bin\cygpath.exe" -w /tmp } # Test concurrent access (run in two PowerShell windows simultaneously) 1..30 | ForEach-Object { $t = Measure-Command { & "C:\Program Files\Git\usr\bin\cygpath.exe" -w /tmp } Write-Host "$_: $($t.TotalSeconds)s" } ``` ## Related Resources - Cygwin slowness on Windows (SuperUser) - Cygpath documentation ## Contact Report generated during debugging session with Claude Code (Opus 4.5).

Measure-Command { & "C:\Program Files\Git\bin\bash.exe" -c "echo hello" } , in my windows TotalMilliseconds : 121.2469 . but claude code read file really very slow when need read multi files. @honix

@honix i add CLAUDE_CODE_GIT_BASH_PATH=C:\Program Files\Git\usr\bin\bash.exe in env and C:\Program Files\Git\usr\bin in path , become a bit smoother

@honix One FileRead call invoked cygpath -u over 20 times, causing extremely slow file reading.

It seems it much better in recent versions of Claude Code. The 2.1.6 (Claude Code) doesnt hangs file reads or something, it feels smooth now.

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