JDWP: update thread synchronization

This CL ensures only one thread can do JDWP stuff at a time: either
processing a command coming from the debugger (JDWP thread) or
sending an event (breakpoint, class prepare, etc) to the debugger
before suspending.

The JDWP thread now uses AcquireJdwpTokenForCommand and
ReleaseJdwpTokenForCommand, respectively acquiring and releasing the
token used for synchronization. On the other hand, the event threads
now use AcquireJdwpTokenForEvent and ReleaseJdwpTokenForEvent.

During an invoke, the target thread needs to take the JDWP token to
execute the method while it's already held by the JDWP handler thread
waiting for the invocation to complete. To avoid both threads from
waiting for each other (deadlock), the JDWP thread releases the token
and acquires it again after the invocation is complete, so the target
thread can run safely and prevents other threads from sending events.

Bug: 19120467
Change-Id: Ie3208fb940a60573769d494128cf22f0fa30fa61

1 files changed, 6 insertions, 10 deletions

diff --git a/runtime/jdwp/jdwp_main.cc b/runtime/jdwp/jdwp_main.cc
index b04aa6e..b6fedd9 100644
--- a/runtime/jdwp/jdwp_main.cc
+++ b/runtime/jdwp/jdwp_main.cc
@@ -220,12 +220,9 @@ JdwpState::JdwpState(const JdwpOptions* options)
       event_list_lock_("JDWP event list lock", kJdwpEventListLock),
       event_list_(nullptr),
       event_list_size_(0),
-      event_thread_lock_("JDWP event thread lock"),
-      event_thread_cond_("JDWP event thread condition variable", event_thread_lock_),
-      event_thread_id_(0),
-      process_request_lock_("JDWP process request lock"),
-      process_request_cond_("JDWP process request condition variable", process_request_lock_),
-      processing_request_(false),
+      jdwp_token_lock_("JDWP token lock"),
+      jdwp_token_cond_("JDWP token condition variable", jdwp_token_lock_),
+      jdwp_token_owner_thread_id_(0),
       ddm_is_active_(false),
       should_exit_(false),
       exit_status_(0) {
@@ -331,7 +328,7 @@ void JdwpState::ResetState() {
    * Should not have one of these in progress.  If the debugger went away
    * mid-request, though, we could see this.
    */
-  if (event_thread_id_ != 0) {
+  if (jdwp_token_owner_thread_id_ != 0) {
     LOG(WARNING) << "Resetting state while event in progress";
     DCHECK(false);
   }
@@ -382,10 +379,9 @@ bool JdwpState::HandlePacket() {
   ssize_t cc = netStateBase->WritePacket(pReply, replyLength);
 
   /*
-   * We processed this request and sent its reply. Notify other threads waiting for us they can now
-   * send events.
+   * We processed this request and sent its reply so we can release the JDWP token.
    */
-  EndProcessingRequest();
+  ReleaseJdwpTokenForCommand();
 
   if (cc != static_cast<ssize_t>(replyLength)) {
     PLOG(ERROR) << "Failed sending reply to debugger";