How to Use the Command 'ccache' (with Examples)

Ccache is a powerful tool that acts as a compiler cache, specifically for C and C++ codes. It works by caching the results of previous compilations and reusing them when the same compilation is requested again. This can significantly speed up the build process, especially for large projects where parts of the code have not changed. By caching and retrieving object files, ccache reduces compilation times drastically compared to recompiling the entire codebase with every change.

Use Case 1: Show Current Cache Statistics

Code:

ccache --show-stats

Motivation for using the example:

Showing the current cache statistics is valuable for developers who want to understand the performance and effectiveness of ccache in their workflow. This information can help in optimizing cache usage and making informed decisions about cache size adjustments.

Explanation for every argument:

• ccache: This is the command-line tool we are using to interact with the cache for our compilations.
• --show-stats: This argument instructs ccache to display current statistics about the cache, such as hit and miss counts, cache size, and more. This helps in evaluating how often cached data is reused.

Example output:

cache directory                     /home/user/.ccache
cache hit (direct)                  42
cache hit (preprocessed)            18
cache miss                          40
files in cache                      100
cache size                          10.2 MB
max cache size                      500.0 MB

Use Case 2: Clear All Cache

Code:

ccache --clear

Motivation for using the example:

Clearing all cache is necessary when significant changes have been made to a project, or to reclaim disk space. It resets the cache, thus removing all stored objects, which ensures that the subsequent builds do not use outdated compiled data.

Explanation for every argument:

• ccache: Again, this is the tool used for managing compilation caching.
• --clear: This argument clears all cached outputs, effectively resetting the state of the ccache. This might be used when you want to start fresh or face consistent caching issues.

Example output:

Cleared cache

Use Case 3: Reset Statistics

Code:

ccache --zero-stats

Motivation for using the example:

Resetting statistics is useful for starting a new measurement period. For instance, after resolving significant code or configuration changes, a developer may wish to observe the new performance characteristics of ccache without being influenced by previous statistics.

Explanation for every argument:

• ccache: This is the command-line tool being used.
• --zero-stats: This argument resets the statistics collected so far back to zero, which allows the developer to start fresh in tracking the performance of their cache.

Example output:

Stats have been zeroed

Use Case 4: Compile C Code and Cache Compiled Output

Code:

ccache gcc path/to/file.c

Motivation for using the example:

Compiling C code with ccache helps to accelerate subsequent compilation times by storing and reusing the compiled output. This is particularly beneficial during iterative development, where the same code may be compiled multiple times.

Explanation for every argument:

• ccache: Utilizing ccache ensures that compiled outputs are stored and can be reused to save time.
• gcc: This is the GNU Compiler Collection used for compiling C code. It can be replaced with other compilers like g++ for C++.
• path/to/file.c: This specifies the file that needs to be compiled. This path must point to a valid C source file.

Example output:

gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)
Compiling file.c...
Compilation successful, output cached

Conclusion:

Ccache acts as a robust assistant in optimizing the C/C++ development process by enhancing compilation speed and efficiency. With applications such as showing cache statistics, clearing caches, resetting statistics, and accelerating code compilation, developers can achieve faster build times while maintaining control over their caching mechanisms. Each use case of ccache demonstrates its value in different scenarios, providing flexibility and speed to development workflows.