Fix adb hang when subprocess dies early.

* Handling of the subprocess and its FD.
  This fixes http://b/3400254 "Many bugreports getting hung at the end in monkey"
  -  Start up a service thread that waits on the subprocess to terminate,
then closes the FD associated with it.
  -  Have the event handler select() with a timeout so that it can
  detect the closed FD. Select() with no timeout does not return when an FD is closed.
  - Have the event handler force a read on the closed FD to trigger the close sequence.
  - Migrate the "shell:blabla" handling to "#if !ADB_HOST" sections.
* Fix the race around OOM adjusting.
  - Do it in the child before exec() instead of the in the parent as the
   child could already have started or not (no /proc/pid/... yet).
* Allow for multi-threaded D() invocations to not clobber each other.
  - Allow locks across object files.
  - Add lock within D()
* Add some missing close(fd) calls
  - Match similar existing practices near dup2()
* Add extra D() invocations related to FD handling.
* Warn about using debugging as stderr/stdout is used for protocol.

Change-Id: Ie5c4a5e6bfbe3f22201adf5f9a205d32e069bf9d
Signed-off-by: JP Abgrall <jpa@google.com>
diff --git a/adb/commandline.c b/adb/commandline.c
index 5ed1b52..c897efe 100644
--- a/adb/commandline.c
+++ b/adb/commandline.c
@@ -218,7 +218,9 @@
     int len;
 
     while(fd >= 0) {
+        D("read_and_dump(): pre adb_read(fd=%d)\n", fd);
         len = adb_read(fd, buf, 4096);
+        D("read_and_dump(): post adb_read(fd=%d): len=%d\n", fd, len);
         if(len == 0) {
             break;
         }
@@ -246,7 +248,9 @@
 
     for(;;) {
         /* fdi is really the client's stdin, so use read, not adb_read here */
+        D("stdin_read_thread(): pre unix_read(fdi=%d,...)\n", fdi);
         r = unix_read(fdi, buf, 1024);
+        D("stdin_read_thread(): post unix_read(fdi=%d,...)\n", fdi);
         if(r == 0) break;
         if(r < 0) {
             if(errno == EINTR) continue;
@@ -853,6 +857,7 @@
         }
 
         if(argc < 2) {
+            D("starting interactive shell\n");
             r = interactive_shell();
             if (h) {
                 printf("\x1b[0m");
@@ -877,9 +882,12 @@
         }
 
         for(;;) {
+            D("interactive shell loop. buff=%s\n", buf);
             fd = adb_connect(buf);
             if(fd >= 0) {
+                D("about to read_and_dump(fd=%d)\n", fd);
                 read_and_dump(fd);
+                D("read_and_dump() done.\n");
                 adb_close(fd);
                 r = 0;
             } else {
@@ -896,6 +904,7 @@
                     printf("\x1b[0m");
                     fflush(stdout);
                 }
+                D("interactive shell loop. return r=%d\n", r);
                 return r;
             }
         }