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| Author | SHA1 | Message | Date | |
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Martin Kustermann
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b9ad67691c |
[vm/concurrency] Allow bool/null in maps/sets without forcing to rehash copied graphs
Even though all canonical objects can be shared, they might cause re-hashing on the receiver side due to user-defined get:hashCode implementation. This is why we do not consider the canonical bit (of a key in a map) when determining whether rehashing is needed. Though some well-known classes will have a properly behaved get:hashCode, the most important being for kNullCid. => So we'll allow kNullCid, kBoolCid. This makes receiving json data much faster due to not needing to re-hash anymore (was done due to `null` values in the map backing store). TEST=Existing test suite. Change-Id: Ie6d39da7fe27ce8925644cf2c17a3944a9e936b2 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/207080 Reviewed-by: Alexander Aprelev <aam@google.com> Commit-Queue: Martin Kustermann <kustermann@google.com> |
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Martin Kustermann
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430aa20a1f |
[vm/concurrency] Implement a fast transitive object copy for isolate message passing
We use message passing as comunication mechanism between isolates.
The transitive closure of an object to be sent is currently serialized
into a snapshot form and deserialized on the receiver side. Furthermore
the receiver side will re-hash any linked hashmaps in that graph.
If isolate gropus are enabled we have all isolates in a group work on
the same heap. That removes the need to use an intermediate
serialization format. It also removes the need for an O(n) step on the
receiver side.
This CL implements a fast transitive object copy implementation and
makes use of it a message that is to be passed to another isolate stays
within the same isolate group.
In the common case the object graph will fit into new space. So the
copy algorithm will try to take advantage of it by having a fast path
and a fallback path. Both of them effectively copy the graph in BFS
order.
The algorithm works effectively like a scavenge operation, but instead
of first copying the from-object to the to-space and then re-writing the
object in to-space to forward the pointers (which requires us writing to
the to-space memory twice), we only reserve space for to-objects and
then initialize the to-objects to it's final contents, including
forwarded pointers (i.e. write the to-space object only once).
Compared with a scavenge operation (which stores forwarding pointers in
the objects themselves), we use a [WeakTable] to store them. This is the
only remaining expensive part of the algorithm and could be further
optimized. To avoid relying on iterating the to-space, we'll remember
[from, to] addresses.
=> All of this works inside a [NoSafepointOperationScope] and avoids
usages of handles as well as write barriers.
While doing the transitive object copy, we'll share any object we can
safely share (canonical objects, strings, sendports, ...) instead of
copying it.
If the fast path fails (due to allocation failure or hitting) we'll
handlify any raw pointers and continue almost the same algorithm in a
safe way, where GC is possible at every object allocation site and
normal barriers are used for any stores of object pointers.
The copy algorithm uses templates to share the copy logic between the
fast and slow case (same copy routines can work on raw pointers as well
as handles).
There's a few special things to take into consideration:
* If we copy a view on external typed data we need to know the
external typed data address to compute the inner pointer of the
view, so we'll eagerly initialize external typed data.
* All external typed data needs to get a finalizer attached
(irrespective if the object copy suceeds or not) to ensure the
`malloc()`ed data is freed again.
* Transferables will only be transferred on successful transitive
copies. Also they need to attach finalizers to objects (which
requires all objects be in handles).
* We copy linked hashmaps as they are - instead of compressing the
data by removing deleted entries. We may need to re-hash those
hashmaps on the receiver side (similar to the snapshot-based copy
approach) since new object graph will have no identity hash codes
assigned to them. Though if the hashmaps only has sharable objects
as keys (very common, e.g. json) there is no need for re-hashing.
It changes the SendPort.* benchmarks as follows:
```
Benchmark | default | IG | IG + FOC
----------------------------------------------------------------------------------------------------------------------------
SendPort.Send.Nop(RunTimeRaw): | 0.25 us (1 x) | 0.26 us (0.96 x) | 0.25 us (1.00 x)
SendPort.Send.Json.400B(RunTimeRaw): | 4.15 us (1 x) | 1.45 us (2.86 x) | 1.05 us (3.95 x)
SendPort.Send.Json.5KB(RunTimeRaw): | 82.16 us (1 x) | 27.17 us (3.02 x) | 18.32 us (4.48 x)
SendPort.Send.Json.50KB(RunTimeRaw): | 784.70 us (1 x) | 242.10 us (3.24 x) | 165.50 us (4.74 x)
SendPort.Send.Json.500KB(RunTimeRaw): | 8510.4 us (1 x) | 3083.80 us (2.76 x) | 2311.29 us (3.68 x)
SendPort.Send.Json.5MB(RunTimeRaw): | 122381.33 us (1 x) | 62959.40 us (1.94 x) | 55492.10 us (2.21 x)
SendPort.Send.BinaryTree.2(RunTimeRaw): | 1.91 us (1 x) | 0.92 us (2.08 x) | 0.72 us (2.65 x)
SendPort.Send.BinaryTree.4(RunTimeRaw): | 6.32 us (1 x) | 2.70 us (2.34 x) | 2.10 us (3.01 x)
SendPort.Send.BinaryTree.6(RunTimeRaw): | 25.24 us (1 x) | 10.47 us (2.41 x) | 8.61 us (2.93 x)
SendPort.Send.BinaryTree.8(RunTimeRaw): | 104.08 us (1 x) | 41.08 us (2.53 x) | 33.51 us (3.11 x)
SendPort.Send.BinaryTree.10(RunTimeRaw): | 373.39 us (1 x) | 174.11 us (2.14 x) | 134.75 us (2.77 x)
SendPort.Send.BinaryTree.12(RunTimeRaw): | 1588.64 us (1 x) | 893.18 us (1.78 x) | 532.05 us (2.99 x)
SendPort.Send.BinaryTree.14(RunTimeRaw): | 6849.55 us (1 x) | 3705.19 us (1.85 x) | 2507.90 us (2.73 x)
SendPort.Receive.Nop(RunTimeRaw): | 0.67 us (1 x) | 0.69 us (0.97 x) | 0.68 us (0.99 x)
SendPort.Receive.Json.400B(RunTimeRaw): | 4.37 us (1 x) | 0.78 us (5.60 x) | 0.77 us (5.68 x)
SendPort.Receive.Json.5KB(RunTimeRaw): | 45.67 us (1 x) | 0.90 us (50.74 x) | 0.87 us (52.49 x)
SendPort.Receive.Json.50KB(RunTimeRaw): | 498.81 us (1 x) | 1.24 us (402.27 x) | 1.06 us (470.58 x)
SendPort.Receive.Json.500KB(RunTimeRaw): | 5366.02 us (1 x) | 4.22 us (1271.57 x) | 4.65 us (1153.98 x)
SendPort.Receive.Json.5MB(RunTimeRaw): | 101050.88 us (1 x) | 20.81 us (4855.88 x) | 21.0 us (4811.95 x)
SendPort.Receive.BinaryTree.2(RunTimeRaw): | 3.91 us (1 x) | 0.76 us (5.14 x) | 0.74 us (5.28 x)
SendPort.Receive.BinaryTree.4(RunTimeRaw): | 9.90 us (1 x) | 0.79 us (12.53 x) | 0.76 us (13.03 x)
SendPort.Receive.BinaryTree.6(RunTimeRaw): | 33.09 us (1 x) | 0.87 us (38.03 x) | 0.84 us (39.39 x)
SendPort.Receive.BinaryTree.8(RunTimeRaw): | 126.77 us (1 x) | 0.92 us (137.79 x) | 0.88 us (144.06 x)
SendPort.Receive.BinaryTree.10(RunTimeRaw): | 533.09 us (1 x) | 0.94 us (567.12 x) | 0.92 us (579.45 x)
SendPort.Receive.BinaryTree.12(RunTimeRaw): | 2223.23 us (1 x) | 3.03 us (733.74 x) | 3.04 us (731.33 x)
SendPort.Receive.BinaryTree.14(RunTimeRaw): | 8945.66 us (1 x) | 4.03 us (2219.77 x) | 4.30 us (2080.39 x)
```
Issue https://github.com/dart-lang/sdk/issues/36097
TEST=vm/dart{,_2}/isolates/fast_object_copy{,2}_test
Change-Id: I835c59dab573d365b8a4b9d7c5359a6ea8d8b0a7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/203776
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
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