On Mon, 2 Nov 2020 22:13:41 GMT, Daniel D. Daugherty <dcu...@openjdk.org> wrote:
>> Self review done. > > ### Gory details about these changes from @fisk and @dcubed-ojdk: > > ### Simplify `ObjectMonitor` List Management: > > - delete per-thread in-use and free-lists. > - delete global free-list and global wait-list; there is a still a global > in-use list; after `ObjectMonitor`s on the global in-use list are deflated, > they are unlinked and added to a function local `GrowableArray` called > `delete_list`; we do a handshake/safepoint with all JavaThreads and that > makes all the `ObjectMonitor`s on the `delete_list` safe for deletion; > lastly, we delete all the `ObjectMonitor`s on `delete_list`. > - move async deflation work from the `ServiceThread` to a dedicated > `MonitorDeflationThread`; this prevents `ObjectMonitor` inflation storms from > delaying the work done by the `ServiceThread` for other subsystems; this > means the `ServiceThread` no longer wakes up every > `GuaranteedSafepointInterval` to check for work. > - the `AllocationState` enum is dropped along with the `_allocation_state` > field and associated getters and setters; the simpler list management no > longer requires the allocation state to be tracked. > - the safepoint cleanup phase no longer requests async monitor deflation; > there is no longer a safepoint cleanup task for monitor deflation, but there > is still an auditing/logging hook for debugging purposes. > - delete ObjectSynchronizer functions associated with more complicated list > management: `deflate_global_idle_monitors()`, > `deflate_per_thread_idle_monitors()`, `deflate_common_idle_monitors()`, > `om_flush()`, `prepend_list_to_common()`, > `prepend_list_to_global_free_list()`, `prepend_list_to_global_wait_list()`, > `prepend_list_to_global_in_use_list()`, `prepend_to_common()`, > `prepend_to_om_free_list()`, `prepend_to_om_in_use_list()`, > `take_from_start_of_common()`, `take_from_start_of_global_free_list()`, > `take_from_start_of_om_free_list()` > - delete the spin-lock functions needed by the more complicated list > management. > - delete a number of audit/debug/logging related functions needed by the more > complicated list management. > - restore the barrier related code that needed relocation due to om_flush()'s > access of the weak obj reference; now that om_flush() is gone, the barrier > related code can go back to its more natural place. > > ### Get Rid of Type-Stable Memory (TSM): > > - `ObjectMonitor` now subclasses `CHeapObj<mtInternal>`. > - the `ObjectMonitor` constructor and destructor are now more normal C++! > - delete `ObjectMonitor` functions associated with TSM: `clear()`, > `clear_common()`, `object_addr()`, `Recycle()`, and `set_object()`. > - delete the version of `set_owner_from()` that support two possible old > values since it is no longer needed; we are not recycling deflated > `ObjectMonitor`s anymore so there's no longer a possibility of a `NULL` > `_owner` value or a `DEFLATER_MARKER` value on the same code path. > - delete ObjectSynchronizer functions associated with TSM: `om_alloc()`, > `om_release()`, `prepend_block_to_lists()` > - simplify ObjectSynchronizer functions related to TSM: > `deflate_idle_monitors()`, `deflate_monitor_list()`, `inflate()` > > ### Change A Displaced Header is Always at Offset 0 > > - Change `markWord::displaced_mark_helper()` and > `markWord::set_displaced_mark_helper()` to no longer assume that the > displaced header in a `BasicLock` or `ObjectMonitor` is at offset 0. > - ObjectMonitor::header_addr() no longer requires the offset to be zero. > > ### New Diagnostic Options > > - `AvgMonitorsPerThreadEstimate` - Used to estimate a variable ceiling based > on number of threads for use with `MonitorUsedDeflationThreshold`; default is > 1024, 0 is off, range is 0..max_jint. The current count of inflated > `ObjectMonitor`s and the ceiling are used to determine whether the in-use > ratio is higher than `MonitorUsedDeflationThreshold` (default 90). > - `MonitorDeflationMax` - The maximum number of `ObjectMonitor`s to deflate, > unlink and delete at one time; default is 1 million; range is 1024..max_jint. Rebased the project to jdk-16+23. Local macOS and Linux-X64 builds and KitchensinkSanity runs pass. Kicking off a new round of Mach5 testing... @coleenp, @dholmes-ora, @fisk, and @robehn - as usual for ObjectMonitor stuff, your reviews would be greatly appreciated. ------------- PR: https://git.openjdk.java.net/jdk/pull/642
