C and C++ compilers aren’t the fastest pieces of software out there and there’s no lack of programmer jokes based on tedium of waiting for their work to complete.
There are ways to fix the pain though - one of them is ccache. CCache improves compilation times by caching previously built object files in private cache and reusing them when you’re recompiling same objects with same parameters. Obviously it will not help if you’re compiling the code for the first time and it also won’t help if you often change compilation flags. Most C/C++ development however involves recompiling same object files with the same parameters and ccache helps alot.
For illustration, here’s the comparison of first and subsequent compilation times of a largish C++ project:
Original run with empty cache:
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$ make -j9 ... real 0m56.684s user 5m31.996s sys 0m41.638s |
Recompilation with warm cache:
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$ make -j9 ... real 0m5.929s user 0m11.896s sys 0m8.722s |
Installation
CCache is available in repositories on pretty much all distributions. On OS X use homebrew:
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$ brew install ccache |
and on Debian-based distros use apt:
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$ apt-get install ccache |
CMake configuration
After ccache is installed, you need to tell CMake to use it as a wrapper for the compiler. Add these lines to your CMakeLists.txt:
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# Configure CCache if available find_program(CCACHE_FOUND ccache) if(CCACHE_FOUND) set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache) set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache) endif(CCACHE_FOUND) |
Rerun cmake and next make should use ccache for wrapper.
Usage with Android NDK
CCache can even be used on Android NDK - you just need to export NDK_CCACHE environment variable with path to ccache binary. ndk-build script will automatically use it. E.g.
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$ export NDK_CCACHE=/usr/local/bin/ccache $ ndk-build -j9 |
(Note that on Debian/Ubuntu the path will probably be /usr/bin/ccache)
CCache statistics
To see if ccache is really working, you can use ccache -s command, which will display ccache statistics:
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cache directory /Users/jernej/.ccache primary config /Users/jernej/.ccache/ccache.conf secondary config (readonly) /usr/local/Cellar/ccache/3.2.2/etc/ccache.conf cache hit (direct) 77826 cache hit (preprocessed) 17603 cache miss 46999 called for link 18 compile failed 45 ccache internal error 1 preprocessor error 62 unsupported source language 204 files in cache 48189 cache size 1.2 GB max cache size 20.0 GB |
On second and all subsequent compilations the “cache hit” values should increase and thus show that ccache is working.