Revert^4 "Add spin loop to mutex, overhaul monitor"
This reverts commit ead89ef62768faa06fedd279b86bccbed1464673.
PS1 is identical to Revert^2.
This fixes a shutdown issue caused by prematurely hanging when we
block while trying to acquire system mutexes during shutdown.
Only refuse to wake up after shutdown is well under way.
Bug: 140590186
Bug: 121302864
Test: Build and boot AOSP.
Test: art/test/testrunner/testrunner.py --host -b -t 1932-monitor-events-misc
Test: art/test/testrunner/testrunner.py --host -b -t 004-ThreadStress
Test: art/test/testrunner/testrunner.py --host -b -t 132-daemon-locks-shutdown
Test: 132-daemon-locks-shutdown repeated with increased thread counts and multiple
concurrent tests.
Change-Id: Ic19d32652a2a05c1ca843b3e9c6e29e6770262da
diff --git a/runtime/lock_word.h b/runtime/lock_word.h
index ac7890c..30559a0 100644
--- a/runtime/lock_word.h
+++ b/runtime/lock_word.h
@@ -42,6 +42,7 @@
* |10|9|8|765432109876|5432109876543210|
* |00|m|r| lock count |thread id owner |
*
+ * The lock count is zero, but the owner is nonzero for a simply held lock.
* When the lock word is in the "fat" state and its bits are formatted as follows:
*
* |33|2|2|2222222211111111110000000000|
@@ -72,7 +73,8 @@
kMarkBitStateSize = 1,
// Number of bits to encode the thin lock owner.
kThinLockOwnerSize = 16,
- // Remaining bits are the recursive lock count.
+ // Remaining bits are the recursive lock count. Zero means it is locked exactly once
+ // and not recursively.
kThinLockCountSize = 32 - kThinLockOwnerSize - kStateSize - kReadBarrierStateSize -
kMarkBitStateSize,
@@ -234,7 +236,8 @@
// Return the owner thin lock thread id.
uint32_t ThinLockOwner() const;
- // Return the number of times a lock value has been locked.
+ // Return the number of times a lock value has been re-locked. Only valid in thin-locked state.
+ // If the lock is held only once the return value is zero.
uint32_t ThinLockCount() const;
// Return the Monitor encoded in a fat lock.