Android应用程序组件Content Provider的启动过程源代码分析（3）

系统管理员 2022-04-03 10:16 211阅读 0赞

Step 7. ActivityManagerService.getContentProviderImpl

这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中：

1.  public final class ActivityManagerService extends ActivityManagerNative 
2.  implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback \{ 
3.   ...... 
4.  
5.  private final ContentProviderHolder getContentProviderImpl( 
6.   IApplicationThread caller, String name) \{ 
7.   ContentProviderRecord cpr; 
8.   ProviderInfo cpi = null; 
9.  
10. synchronized(this) \{ 
11.  Proce\*\*\*ecord r = null; 
12. if (caller != null) \{ 
13.  r = getRecordForAppLocked(caller); 
14.  ...... 
15.  \} 
16. 
17. // First check if this content provider has been published... 
18.  cpr = mProvidersByName.get(name); 
19. if (cpr != null) \{ 
20.  ...... 
21.  \} else \{ 
22. try \{ 
23.  cpi = AppGlobals.getPackageManager(). 
24.  resolveContentProvider(name, 
25.  STOCK\_PM\_FLAGS | PackageManager.GET\_URI\_PERMISSION\_PATTERNS); 
26.  \} catch (RemoteException ex) \{ 
27.  \} 
28.  ...... 
29.  \} 
30. 
31.  cpr = mProvidersByClass.get(cpi.name); 
32. final boolean firstClass = cpr == null; 
33. if (firstClass) \{ 
34. try \{ 
35.  ApplicationInfo ai = 
36.  AppGlobals.getPackageManager(). 
37.  getApplicationInfo( 
38.  cpi.applicationInfo.packageName, 
39.  STOCK\_PM\_FLAGS); 
40.  ...... 
41.  cpr = new ContentProviderRecord(cpi, ai); 
42.  \} catch (RemoteException ex) \{ 
43. // pm is in same process, this will never happen. 
44.  \} 
45.  \} 
46. 
47. if (r != null && cpr.canRunHere(r)) \{ 
48. // If this is a multiprocess provider, then just return its 
49. // info and allow the caller to instantiate it. Only do 
50. // this if the provider is the same user as the caller's 
51. // process, or can run as root (so can be in any process). 
52. return cpr; 
53.  \} 
54. 
55.  ...... 
56. 
57. // This is single process, and our app is now connecting to it. 
58. // See if we are already in the process of launching this 
59. // provider. 
60. final int N = mLaunchingProviders.size(); 
61. int i; 
62. for (i=0; i<N; i++) \{ 
63. if (mLaunchingProviders.get(i) == cpr) \{ 
64. break; 
65.  \} 
66.  \} 
67. 
68. // If the provider is not already being launched, then get it 
69. // started. 
70. if (i >= N) \{ 
71. final long origId = Binder.clearCallingIdentity(); 
72.  Proce\*\*\*ecord proc = startProcessLocked(cpi.processName, 
73.  cpr.appInfo, false, 0, "content provider", 
74. new ComponentName(cpi.applicationInfo.packageName, 
75.  cpi.name), false); 
76.  ...... 
77.  mLaunchingProviders.add(cpr); 
78.  ...... 
79.  \} 
80. 
81. // Make sure the provider is published (the same provider class 
82. // may be published under multiple names). 
83. if (firstClass) \{ 
84.  mProvidersByClass.put(cpi.name, cpr); 
85.  \} 
86.  cpr.launchingApp = proc; 
87.  mProvidersByName.put(name, cpr); 
88. 
89.  ...... 
90.  \} 
91. 
92. // Wait for the provider to be published... 
93. synchronized (cpr) \{ 
94. while (cpr.provider == null) \{ 
95.  ...... 
96. try \{ 
97.  cpr.wait(); 
98.  \} catch (InterruptedException ex) \{ 
99.  \} 
100.  \} 
101.  \} 
102. 
103. return cpr; 
104.  \} 
105. 
106.  ...... 
107. \}

这个函数比较长，我们一步一步地分析。  
 函数首先是获取调用者的进程记录块信息：

1.  Proce\*\*\*ecord r = **null**; 
2.  **if** (caller != **null**) \{ 
3.   r = getRecordForAppLocked(caller); 
4.   ...... 
5.  \}

在我们这个情景中，要获取的就是应用程序Article的进程记录块信息了，后面会用到。

在ActivityManagerService中，有两个成员变量是用来保存系统中的Content Provider信息的，一个是mProvidersByName，一个是mProvidersByClass，前者是以Content Provider的authoriry值为键值来保存的，后者是以Content Provider的类名为键值来保存的。一个Content Provider可以有多个authority，而只有一个类来和它对应，因此，这里要用两个Map来保存，这里为了方便根据不同条件来快速查找而设计的。下面的代码就是用来检查要获取的Content Provider是否已经加存在的了：

1.  // First check if this content provider has been published... 
2.  cpr = mProvidersByName.get(name); 
3.  if (cpr != null) \{ 
4.   ...... 
5.  \} else \{ 
6.  try \{ 
7.   cpi = AppGlobals.getPackageManager(). 
8.   resolveContentProvider(name, 
9.   STOCK\_PM\_FLAGS | PackageManager.GET\_URI\_PERMISSION\_PATTERNS); 
10.  \} catch (RemoteException ex) \{ 
11.  \} 
12.  ...... 
13. \} 
14. 
15. cpr = mProvidersByClass.get(cpi.name); 
16. final boolean firstClass = cpr == null; 
17. if (firstClass) \{ 
18. try \{ 
19.  ApplicationInfo ai = 
20.  AppGlobals.getPackageManager(). 
21.  getApplicationInfo( 
22.  cpi.applicationInfo.packageName, 
23.  STOCK\_PM\_FLAGS); 
24.  ...... 
25.  cpr = new ContentProviderRecord(cpi, ai); 
26.  \} catch (RemoteException ex) \{ 
27. // pm is in same process, this will never happen. 
28.  \} 
29. \}

在我们这个情景中，由于是第一次调用ArticlesProvider接口，因此，在mProvidersByName和mProvidersByClass两个Map中都不存在ArticlesProvider的相关信息，因此，这里会通过AppGlobals.getPackageManager函数来获得PackageManagerService服务接口，然后分别通过它的resolveContentProvider和getApplicationInfo函数来分别获取ArticlesProvider应用程序的相关信息，分别保存在cpi和cpr这两个本地变量中。这些信息都是在安装应用程序的过程中保存下来的，具体可以参考 [Android应用程序安装过程源代码分析][Android] 一文。

[Android]: http://shyluo.blog.51cto.com/5725845/966518