如何让B2构建器默认启用-jN并行编译Boost，支持动态获取核心数？

Absolutely, you can configure B2 to run parallel builds automatically—no need to type -j4 every time. Even better, you can set it to dynamically use all available cores instead of hardcoding a number. Here are the most straightforward methods:

1. Use Environment Variables (Simplest Approach) #

B2 checks for the B2_JOBS or JOBS environment variables to determine default parallel jobs. You can set this dynamically in your shell configuration:

• For Linux/WSL: Add this line to your ~/.bashrc or ~/.profile file:

  export B2_JOBS=$(nproc)
  

  nproc outputs the number of available CPU cores automatically.

• For macOS: Use sysctl instead of nproc:

  export B2_JOBS=$(sysctl -n hw.ncpu)
  

After reloading your shell (or running source ~/.bashrc), typing ./b2 will automatically use all your cores for parallel builds.

2. Configure via B2's Jam Configuration Files #

If you prefer setting this directly in B2's config (instead of shell env vars), you can modify user-config.jam or create a site-config.jam file:

1. Locate your user-config.jam (usually in ~/.user-config.jam or Boost's tools/build/src directory, depending on your setup).
2. Add these lines to the file:

   # Dynamically get core count and set default jobs
   import os ;
   local core_count = [ os.command-output nproc ] ; # Use "sysctl -n hw.ncpu" for macOS
   set-option jobs : $(core_count) ;
   

This uses B2's native Jam language to run nproc (or the macOS equivalent) and set the default jobs option to the result.

3. Create a Wrapper Script (Flexible Alternative) #

If you want a portable way that doesn't rely on shell configs or Jam files, make a simple wrapper script:

1. Create a file named b2-auto (or whatever you prefer) in your Boost directory:

   #!/bin/bash
   # Auto-use all cores for B2 builds
   CORE_COUNT=$(nproc) # Replace with "sysctl -n hw.ncpu" on macOS
   ./b2 -j$CORE_COUNT "$@"
   

2. Make it executable:

   chmod +x b2-auto
   

Now run ./b2-auto instead of ./b2—it'll use all cores and still pass through any other arguments you add (like install or variant=release).

Important Note #

If you ever manually specify -jN (e.g., ./b2 -j2), that value will override your default setting—so you can still force a specific number of jobs when needed.

内容的提问来源于stack exchange，提问作者einpoklum