9f601a917c8878204482c37aec7005054b6776fa |
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12-Feb-2011 |
buzbee <buzbee@google.com> |
Interpreter restructuring: eliminate InterpState The key datastructure for the interpreter is InterpState. This change eliminates it, merging its data with the Thread structure. Here's why: In principio creavit Fadden Thread et InterpState. And it was good. Thread holds thread-private state, while InterpState captures data associated with a Dalvik interpreter activation. Because JNI calls can result in nested interpreter invocations, we can have more than one InterpState for each actual thread. InterpState was relatively small, and it all worked well. It was used enough that in the Arm version a register (rGLUE) was dedicated to it. Then, along came the JIT guys, who saw InterpState as a convenient place to dump all sorts of useful data that they wanted quick access to through that dedicated register. InterpState grew and grew. In terms of space, this wasn't a big problem - but it did mean that the initialization cost of each interpreter activation grew as well. For applications that do a lot of callbacks from native code into Dalvik, this is measurable. It's also mostly useless cost because much of the JIT-related InterpState initialization was setting up useful constants - things that don't need to be saved and restored all the time. The biggest problem, though, deals with thread control. When something interesting is happening that needs all threads to be stopped (such as GC and debugger attach), we have access to all of the Thread structures, but we don't have access to all of the InterpState structures (which may be buried/nested on the native stack). As a result, polling for thread suspension is done via a one-indirection pointer chase. InterpState itself can't hold the stop bits because we can't always find it, so instead it holds a pointer to the global or thread-specific stop control. Yuck. With this change, we eliminate InterpState and merge all needed data into Thread. Further, we replace the decidated rGLUE register with a pointer to the Thread structure (rSELF). The small subset of state data that needs to be saved and restored across nested interpreter activations is collected into a record that is saved to the interpreter frame, and restored on exit. Further, these small records are linked together to allow tracebacks to show nested activations. Old InterpState variables that simply contain useful constants are initialized once at thread creation time. This CL is large enough by itself that the new ability to streamline suspend checks is not done here - that will happen in a future CL. Here we just focus on consolidation. Change-Id: Ide6b2fb85716fea454ac113f5611263a96687356
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