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| -rw-r--r-- | docs/debugger.html | 15 |
1 files changed, 7 insertions, 8 deletions
diff --git a/docs/debugger.html b/docs/debugger.html index 523c7123d..033eeb62d 100644 --- a/docs/debugger.html +++ b/docs/debugger.html @@ -55,14 +55,13 @@ A connection from DDMS alone doesn't result in a change in VM behavior, but when the VM sees debugger packets it allocates additional data structures and may switch to a different implementation of the interpreter. </p><p> -Because Dalvik maps bytecode into memory read-only, some common -techniques are difficult to implement without allocating additional memory. -For example, suppose the debugger sets a breakpoint in a method. The -quick way to handle this is to insert a breakpoint instruction directly -into the code. When the instruction is reached, the breakpoint handler -engages. Without this, it's necessary to perform an "is there a breakpoint -here" scan. Even with some optimizations, the debug-enabled interpreter -is much slower than the regular interpreter (perhaps 5x). +Pre-Flan implementations of the Dalvik VM used read-only memory mappings +for all bytecode, which made it necessary to scan for breakpoints by +comparing the program counter to a set of addresses. In Flan this was +changed to allow insertion of breakpoint opcodes. This allows the VM +to execute code more quickly, and does away with the hardcoded limit +of 20 breakpoints. Even with this change, however, the debug-enabled +interpreter is much slower than the regular interpreter (perhaps 5x). </p><p> The JDWP protocol is stateless, so the VM handles individual debugger requests as they arrive, and posts events to the debugger as they happen. |