Source code analysis of Android Application Process Startup Process (6)

The preceding result obtained from peers. get (index) is a ZygoteConnection object, indicating a Socket connection.

Therefore, the next step is to call the ZygoteConnection. runOnce function for further processing.

Step 6. ZygoteConnection. runOnce

This function is defined in the frameworks/base/core/java/com/android/internal/OS/ZygoteConnection. java file:

 
 

  
  
[java] view plaincopyclass ZygoteConnection { 
  
  
...... 
  
  
boolean runOnce() throws ZygoteInit.MethodAndArgsCaller { 
  
  
String args[]; 
  
  
Arguments parsedArgs = null; 
  
  
FileDescriptor[] descriptors; 
  
  
try { 
  
  
args = readArgumentList(); 
  
  
descriptors = mSocket.getAncillaryFileDescriptors(); 
  
  
} catch (IOException ex) { 
  
  
...... 
  
  
return true; 
  
  
} 
  
  
...... 
  
  
/** the stderr of the most recent request, if avail */ 
  
  
PrintStream newStderr = null; 
  
  
if (descriptors != null && descriptors.length >= 3) { 
  
  
newStderr = new PrintStream( 
  
  
new FileOutputStream(descriptors[2])); 
  
  
} 
  
  
int pid; 
  
  
try { 
  
  
parsedArgs = new Arguments(args); 
  
  
applyUidSecurityPolicy(parsedArgs, peer); 
  
  
applyDebuggerSecurityPolicy(parsedArgs); 
  
  
applyRlimitSecurityPolicy(parsedArgs, peer); 
  
  
applyCapabilitiesSecurityPolicy(parsedArgs, peer); 
  
  
int[][] rlimits = null; 
  
  
if (parsedArgs.rlimits != null) { 
  
  
rlimits = parsedArgs.rlimits.toArray(intArray2d); 
  
  
} 
  
  
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, 
  
  
parsedArgs.gids, parsedArgs.debugFlags, rlimits); 
  
  
} catch (IllegalArgumentException ex) { 
  
  
...... 
  
  
} catch (ZygoteSecurityException ex) { 
  
  
...... 
  
  
} 
  
  
if (pid == 0) { 
  
  
// in child 
  
  
handleChildProc(parsedArgs, descriptors, newStderr); 
  
  
// should never happen 
  
  
return true; 
  
  
} else { /* pid != 0 */ 
  
  
// in parent...pid of < 0 means failure 
  
  
return handleParentProc(pid, descriptors, parsedArgs); 
  
  
} 
  
  
} 
  
  
...... 
  
  
} 
 
 

Here is where the process is actually created:

 
 

  
  
[java] view plaincopypid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, 
  
  
parsedArgs.gids, parsedArgs.debugFlags, rlimits); 
 
 

Readers with Linux development experience can easily understand this function call. This function creates a process and has two return values. One is returned in the current process, one is returned in the newly created process, that is, returned in the current process sub-process. The return value in the current process is the pid value of the newly created sub-process, the return value in the sub-process is 0. Because we only care about the creation of new processes, we can continue to look at the sub-process execution path:

 
 

  
  
[java] view plaincopy if (pid == 0) { 
  
  
// in child 
  
  
handleChildProc(parsedArgs, descriptors, newStderr); 
  
  
// should never happen 
  
  
return true; 
  
  
} else { /* pid != 0 */ 
  
  
...... 
  
  
} 
 
 

The handleChildProc function is called here.