/** * Keep track of all those APKs everywhere. * <p> * Internally there are two important locks: * <ul> * <li>{@link #mPackages} is used to guard all in-memory parsed package details * and other related state. It is a fine-grained lock that should only be held * momentarily, as it's one of the most contended locks in the system. * <li>{@link #mInstallLock} is used to guard all {@code installd} access, whose * operations typically involve heavy lifting of application data on disk. Since * {@code installd} is single-threaded, and it's operations can often be slow, * this lock should never be acquired while already holding {@link #mPackages}. * Conversely, it's safe to acquire {@link #mPackages} momentarily while already * holding {@link #mInstallLock}. * </ul> * Many internal methods rely on the caller to hold the appropriate locks, and * this contract is expressed through method name suffixes: * <ul> * <li>fooLI(): the caller must hold {@link #mInstallLock} * <li>fooLIF(): the caller must hold {@link #mInstallLock} and the package * being modified must be frozen * <li>fooLPr(): the caller must hold {@link #mPackages} for reading * <li>fooLPw(): the caller must hold {@link #mPackages} for writing * </ul> * <p> * Because this class is very central to the platform's security; please run all * CTS and unit tests whenever making modifications: * * <pre> * $ runtest -c android.content.pm.PackageManagerTests frameworks-core * $ cts-tradefed run commandAndExit cts -m CtsAppSecurityHostTestCases * </pre> */
註釋裏面說的比較清楚Pms有兩把鎖，一把叫mPackages，是fine-grained lock（細粒度的鎖）。 另外一把是mInstallLock，它是一把重量級的鎖。 另外還有四個方法實例表示該方法持有什麼樣的鎖，分別是：java
- fooLI() LI結尾表示調用者必須持有mInstallLock這把鎖
- fooLIF() LIF結尾調用者必須持有mInstallLock 這把鎖，而且必須凍結（凍結表示禁止啓動）要修改的軟件包。
- fooLPr() LPr結尾表示必須持有mPackages才能夠調用，而且該方法只讀mPackages鎖保護的數據。
- fooLPw() LPw結尾表示必須持有mPackages才能夠調用，而且該方法會修改mPackages鎖保護的數據。
另外因爲mPackages爲細粒度的鎖， mInstallLock爲重量級鎖，因此不該該在持有 mPackages鎖的狀況下再去獲取mInstallLock，不然mPackages也會變成重量級。android
上述都不是重點， 重點是Pms到底如何使用這兩把鎖， 如今由我來給你們說明。express
PackageManagerService主要有兩項工做：
1 應用安裝卸載： mInstallLock 主要保證這個流程是串行執行。而這個過程會修改mPackages鎖保護的數據，mPackages保證安裝卸載過程當中查詢數據正確。
2 應用信息查詢：mPackages 也是保證查詢數據正確，這個過程不會修改mPackages保護的數據。
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