Check point root marking.
Added thread list checkpoint function, this goes through every thread and runs
the checkpoint on each thread. Threads that are runnable run the checkpoint
callback themselves in the next suspend check, while suspended threads are
left suspended but have the callback called on them.
Added a checkpoint visitor member to each thread, this visitor called when the
checkpoint request flag is set during transitions to suspended from runnable.
Using the checkpoint to mark the roots reduces the first pause of partial /
full gc to around 1 ms.
Change-Id: I97239cc72ee0e4a3397e9138a62ee559268dce0a
diff --git a/src/thread.cc b/src/thread.cc
index cea919f..67773a5 100644
--- a/src/thread.cc
+++ b/src/thread.cc
@@ -555,6 +555,19 @@
}
}
+bool Thread::RequestCheckpoint(CheckpointFunction* function) {
+ CHECK(!ReadFlag(kCheckpointRequest)) << "Already have a pending checkpoint request";
+ checkpoint_function_ = function;
+ union StateAndFlags old_state_and_flags = state_and_flags_;
+ // We must be runnable to request a checkpoint.
+ old_state_and_flags.as_struct.state = kRunnable;
+ union StateAndFlags new_state_and_flags = old_state_and_flags;
+ new_state_and_flags.as_struct.flags |= kCheckpointRequest;
+ int succeeded = android_atomic_cmpxchg(old_state_and_flags.as_int, new_state_and_flags.as_int,
+ &state_and_flags_.as_int);
+ return succeeded == 0;
+}
+
void Thread::FullSuspendCheck() {
VLOG(threads) << this << " self-suspending";
// Make thread appear suspended to other threads, release mutator_lock_.
@@ -570,7 +583,20 @@
DCHECK_EQ(this, Thread::Current());
// Change to non-runnable state, thereby appearing suspended to the system.
DCHECK_EQ(GetState(), kRunnable);
- state_and_flags_.as_struct.state = new_state;
+ union StateAndFlags old_state_and_flags;
+ union StateAndFlags new_state_and_flags;
+ do {
+ old_state_and_flags = state_and_flags_;
+ // Copy over flags and try to clear the checkpoint bit if it is set.
+ new_state_and_flags.as_struct.flags = old_state_and_flags.as_struct.flags & ~kCheckpointRequest;
+ new_state_and_flags.as_struct.state = new_state;
+ } while (android_atomic_cmpxchg(old_state_and_flags.as_int, new_state_and_flags.as_int,
+ &state_and_flags_.as_int) != 0);
+ // If we toggled the checkpoint flag we must have cleared it.
+ uint16_t flag_change = new_state_and_flags.as_struct.flags ^ old_state_and_flags.as_struct.flags;
+ if ((flag_change & kCheckpointRequest) != 0) {
+ RunCheckpointFunction();
+ }
// Release share on mutator_lock_.
Locks::mutator_lock_->SharedUnlock(this);
}
@@ -935,6 +961,7 @@
pthread_self_(0),
no_thread_suspension_(0),
last_no_thread_suspension_cause_(NULL),
+ checkpoint_function_(0),
thread_exit_check_count_(0) {
CHECK_EQ((sizeof(Thread) % 4), 0U) << sizeof(Thread);
state_and_flags_.as_struct.flags = 0;