Fix hang when using --exec flag in Nix sandboxed builds

The busy-wait loop at await.c:900-906 was spinning at 100% CPU without
yielding, preventing the exec thread from completing in constrained
environments like Nix's sandboxed builds.

Added msleep(10) to the loop to allow the exec thread to get CPU time.

This fixes 4 tests that were timing out in Nix builds:
- test_placeholder_in_exec
- test_exec_runs_on_success
- test_exec_with_fail_flag
- test_exec_with_output

All 46 tests now pass in nix-build.

Also added default.nix and shell.nix for Nix package maintainers.

Fixes #18

Author: slavaGanzin

README.md

@@ -1,5 +1,5 @@
 # await
-40K, small memory footprint, single binary that run list of commands in parallel and waits for their termination
+ 36K	build/await, small memory footprint, single binary that run list of commands in parallel and waits for their termination
 
 <!-- DO NOT CHANGE THIS FILE IS GENERATED BY ./hooks/pre-commit -->
 

await.c

@@ -903,6 +903,7 @@ int main(int argc, char *argv[]) {
             fprintf(stderr, "\033[%dB\r", args.nCommands + 1);
             return 0;
           }
+          msleep(10);  // Sleep 10ms to allow exec thread to run
         }
       }
     }

default.nix

@@ -0,0 +1,61 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.stdenv.mkDerivation {
+  pname = "await";
+  version = "2.1.0";
+
+  src = ./.;
+
+  nativeBuildInputs = with pkgs; [
+    cmake
+  ];
+
+  nativeCheckInputs = with pkgs; [
+    python312
+    python312Packages.pytest
+  ];
+
+  doCheck = true;
+
+  preCheck = ''
+    # TMPDIR is already set by Nix to a writable sandbox location
+    # Just replace the await path for tests
+    substituteInPlace ../tests/test_await.py \
+      --replace-fail "../await" "../build/await"
+  '';
+
+  checkPhase = ''
+    runHook preCheck
+
+    # Return to source directory since build happens in ./build
+    cd ..
+    cd tests
+    python -m pytest test_await.py -v
+
+    runHook postCheck
+  '';
+
+  installPhase = ''
+    # After tests we're in tests/, go back to source root
+    cd ..
+
+    mkdir -p $out/bin
+    cp build/await $out/bin/
+
+    mkdir -p $out/share/bash-completion/completions
+    cp build/await.bash $out/share/bash-completion/completions/await
+
+    mkdir -p $out/share/fish/vendor_completions.d
+    cp build/await.fish $out/share/fish/vendor_completions.d/
+
+    mkdir -p $out/share/zsh/site-functions
+    cp build/await.zsh $out/share/zsh/site-functions/_await
+  '';
+
+  meta = with pkgs.lib; {
+    description = "Runs list of commands and waits for their termination";
+    homepage = "https://github.com/slavaGanzin/await";
+    license = licenses.mit;
+    platforms = platforms.unix;
+  };
+}

shell.nix

@@ -0,0 +1,24 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    cmake
+    gcc
+    python312
+    python312Packages.pytest
+    bash
+  ];
+
+  shellHook = ''
+    echo "Nix development environment for await"
+    echo "Building with CMake..."
+
+    # Set up similar to Nix build environment
+    export TMPDIR="''${TMPDIR:-/tmp}"
+    export HOME="''${HOME:-/build}"
+
+    echo "TMPDIR: $TMPDIR"
+    echo "Run 'mkdir build && cd build && cmake .. && make' to build"
+    echo "Run 'cd tests && pytest test_await.py -v' to run tests"
+  '';
+}