mirror of
https://github.com/dart-lang/sdk
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d7df61e042
This reverts commit 7fe44864d6
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Reason for revert: https://github.com/flutter/flutter/issues/106957
Original change's description:
> [vm] Generate event ids for synchronous begin and end events.
>
> os_signposts needs explicit ids to match begin and end events, whereas all other trace systems do this implicitly.
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> TEST=Instruments
> Bug: https://github.com/dart-lang/sdk/issues/49178
> Change-Id: Ifeeaa1dfe823a0d5668f48b8c584f8bdeef23212
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/249951
> Reviewed-by: Siva Annamalai <asiva@google.com>
> Commit-Queue: Ryan Macnak <rmacnak@google.com>
TBR=rmacnak@google.com,asiva@google.com
Change-Id: Id86959d08b5352b5446b6f294a8302b88b4fa0c8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: https://github.com/dart-lang/sdk/issues/49178
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/250403
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Liam Appelbe <liama@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
Reviewed-by: Liam Appelbe <liama@google.com>
79 lines
2.1 KiB
C++
79 lines
2.1 KiB
C++
// Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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#include "vm/random.h"
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#include "vm/dart.h"
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#include "vm/flags.h"
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#include "vm/os.h"
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namespace dart {
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DEFINE_FLAG(uint64_t,
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random_seed,
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0,
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"Override the random seed for debugging.");
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Random::Random() {
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uint64_t seed = FLAG_random_seed;
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if (seed == 0) {
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Dart_EntropySource callback = Dart::entropy_source_callback();
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if (callback != NULL) {
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if (!callback(reinterpret_cast<uint8_t*>(&seed), sizeof(seed))) {
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// Callback failed. Reset the seed to 0.
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seed = 0;
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}
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}
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}
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if (seed == 0) {
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// We did not get a seed so far. As a fallback we do use the current time.
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seed = OS::GetCurrentTimeMicros();
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}
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Initialize(seed);
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}
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void Random::Initialize(uint64_t seed) {
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ASSERT(seed != 0);
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// Crank the next state a couple of times.
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_state = seed;
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NextState();
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NextState();
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NextState();
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NextState();
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}
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Random::Random(uint64_t seed) {
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Initialize(seed);
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}
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Random::~Random() {
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// Nothing to be done here.
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}
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// The algorithm used here is Multiply with Carry (MWC) with a Base b = 2^32.
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// http://en.wikipedia.org/wiki/Multiply-with-carry
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// The constant A is selected from "Numerical Recipes 3rd Edition" p.348 B1.
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uint64_t Random::NextState() {
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const uint64_t MASK_32 = 0xffffffff;
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const uint64_t A = 0xffffda61;
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uint64_t old_state = _state;
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while (true) {
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const uint64_t state_lo = old_state & MASK_32;
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const uint64_t state_hi = (old_state >> 32) & MASK_32;
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const uint64_t new_state = (A * state_lo) + state_hi;
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if (_state.compare_exchange_weak(old_state, new_state,
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std::memory_order_relaxed,
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std::memory_order_relaxed)) {
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return new_state;
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}
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}
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}
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uint32_t Random::NextUInt32() {
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const uint64_t MASK_32 = 0xffffffff;
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return static_cast<uint32_t>(NextState() & MASK_32);
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}
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} // namespace dart
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