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Commit 87e97ee3 authored by Spencer Low's avatar Spencer Low
Browse files

adb: win32: fix shutdown deadlock 



adb can hang at shutdown due to a deadlock relating to WSACleanup().
This works around the issue by not calling WSACleanup() which shouldn't
be done anyway since threads aren't done using Winsock at shutdown.

A quick way to reproduce the original problem is to run many instances
of adb, many of which will call exit() soon:

  for /l %i in (1,1,20) do @start adb nodaemon server

You may have to boost the 20 to 200, or set ADB_TRACE=1 or use Windows
10 instead of Windows 7, to affect the timing, but eventually there
should be hung adb processes with that repro.

A more complete fix to prevent problems like this from occuring in the
future, would be to additionally do the following:

- Investigate all static destructors that are called when exit() is
  called.

- If they don't do anything important, switch all calls to exit() to
  instead call _exit() and then ban exit() from being called.

Change-Id: Id1be3bf0053809a45f2eca4461e4c35b5ef9388d
Signed-off-by: default avatarSpencer Low <CompareAndSwap@gmail.com>
parent b81c410a

adb/sysdeps_win32.cpp

+15 −12
Original line number Diff line number Diff line
@@ -651,21 +651,11 @@ static int _fh_socket_write(FH f, const void* buf, int len) { 


static int  _winsock_init;



static void

_cleanup_winsock( void )

{

    // TODO: WSAStartup() might be called multiple times and this won't properly

    // cleanup the right number of times. Plus, WSACleanup() probably doesn't

    // make sense since it might interrupt other threads using Winsock (since

    // our various threads are not explicitly cleanly shutdown at process exit).

    WSACleanup();

}



static void

_init_winsock( void )

{

    // TODO: Multiple threads calling this may potentially cause multiple calls

    // to WSAStartup() and multiple atexit() calls.

    // to WSAStartup() which offers no real benefit.

    if (!_winsock_init) {

        WSADATA  wsaData;

        int      rc = WSAStartup( MAKEWORD(2,2), &wsaData);
@@ -673,8 +663,21 @@ _init_winsock( void ) 
            fatal( "adb: could not initialize Winsock: %s",

                   SystemErrorCodeToString( rc ).c_str());

        }

        atexit( _cleanup_winsock );

        _winsock_init = 1;



        // Note that we do not call atexit() to register WSACleanup to be called

        // at normal process termination because:

        // 1) When exit() is called, there are still threads actively using

        //    Winsock because we don't cleanly shutdown all threads, so it

        //    doesn't make sense to call WSACleanup() and may cause problems

        //    with those threads.

        // 2) A deadlock can occur when exit() holds a C Runtime lock, then it

        //    calls WSACleanup() which tries to unload a DLL, which tries to

        //    grab the LoaderLock. This conflicts with the device_poll_thread

        //    which holds the LoaderLock because AdbWinApi.dll calls

        //    setupapi.dll which tries to load wintrust.dll which tries to load

        //    crypt32.dll which calls atexit() which tries to acquire the C

        //    Runtime lock that the other thread holds.

    }

}