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Summary of ChangesHello @waruqi, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request introduces a performance optimization for retrieving environment variables within the Highlights
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Code Review
This pull request introduces caching for os.getenvs() to improve performance by avoiding repeated parsing of environment variables. The implementation correctly invalidates the cache when the environment is modified. However, the new caching mechanism introduces a critical race condition in concurrent environments (e.g., using coroutines), which could lead to a poisoned cache with stale data and result in incorrect build behavior. I have detailed this issue in a review comment and recommended a fix.
xmake/core/base/os.lua
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| local envs = os._ENVS | ||
| if envs == nil then | ||
| envs = {} | ||
| for _, line in ipairs(os._getenvs()) do | ||
| local p = line:find('=', 1, true) | ||
| if p then | ||
| local key = line:sub(1, p - 1):trim() | ||
| -- only translate Path to PATH on windows | ||
| -- @see https://github.com/xmake-io/xmake/issues/3752 | ||
| if os.host() == "windows" and key:lower() == "path" then | ||
| key = key:upper() | ||
| end | ||
| local values = line:sub(p + 1):trim() | ||
| if #key > 0 then | ||
| envs[key] = values | ||
| end | ||
| end | ||
| end | ||
| os._ENVS = envs | ||
| end |
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The new caching mechanism introduces a race condition in a concurrent environment (coroutines) that can lead to a poisoned cache with stale data, potentially causing incorrect build behavior.
Here is a scenario:
- Coroutine A calls
os.getenvs(). It findsos._ENVSisniland starts computing the environment variables by callingos._getenvs(). - While Coroutine A is parsing, Coroutine B calls an environment-modifying function like
os.setenv(). This modifies the process environment and then callsos._notify_envs_changed(), which setsos._ENVStonilto invalidate the cache. - Coroutine A finishes its computation. The data it has is now stale because of Coroutine B's action.
- Coroutine A then sets
os._ENVSto its stale data, poisoning the cache. - Any subsequent call to
os.getenvs()will return incorrect environment variables until the next invalidation.
To fix this, you need to ensure that the check for a nil cache, the computation of the environment variables, and the setting of the cache are atomic. This typically requires a locking mechanism to be used around os.getenvs() and all functions that modify the environment (e.g., os.setenv, os.addenv, etc.).
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As long as there is no process execution, there will be no coroutine switching.
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#6775