1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16#include "lambda/closure_builder.h"
17
18#include "base/macros.h"
19#include "base/value_object.h"
20#include "lambda/art_lambda_method.h"
21#include "lambda/closure.h"
22#include "lambda/shorty_field_type.h"
23#include "runtime/mirror/object_reference.h"
24
25#include <stdint.h>
26#include <vector>
27
28namespace art {
29namespace lambda {
30
31/*
32 * GC support TODOs:
33 * (Although there's some code for storing objects, it is UNIMPLEMENTED(FATAL) because it is
34 * incomplete).
35 *
36 * 1) GC needs to be able to traverse the Closure and visit any references.
37 *    It might be possible to get away with global roots in the short term.
38 *
39 * 2) Add brooks read barrier support. We can store the black/gray/white bits
40 *    in the lower 2 bits of the lambda art method pointer. Whenever a closure is copied
41 *    [to the stack] we'd need to add a cold path to turn it black.
42 *    (since there's only 3 colors, I can use the 4th value to indicate no-refs).
43 *    e.g. 0x0 = gray, 0x1 = white, 0x2 = black, 0x3 = no-nested-references
44 *    - Alternatively the GC can mark reference-less closures as always-black,
45 *      although it would need extra work to check for references.
46 */
47
48void ClosureBuilder::CaptureVariableObject(mirror::Object* object) {
49  auto compressed_reference = mirror::CompressedReference<mirror::Object>::FromMirrorPtr(object);
50  ShortyFieldTypeTraits::MaxType storage = 0;
51
52  static_assert(sizeof(storage) >= sizeof(compressed_reference),
53                "not enough room to store a compressed reference");
54  memcpy(&storage, &compressed_reference, sizeof(compressed_reference));
55
56  values_.push_back(storage);
57  size_ += kObjectReferenceSize;
58
59  static_assert(kObjectReferenceSize == sizeof(compressed_reference), "reference size mismatch");
60
61  // TODO: needs more work to support concurrent GC
62  if (kIsDebugBuild) {
63    if (kUseReadBarrier) {
64      UNIMPLEMENTED(FATAL) << "can't yet safely capture objects with read barrier";
65    }
66  }
67
68  shorty_types_ += ShortyFieldType::kObject;
69}
70
71void ClosureBuilder::CaptureVariableLambda(Closure* closure) {
72  DCHECK(closure != nullptr);  // null closures not allowed, target method must be null instead.
73  values_.push_back(reinterpret_cast<ShortyFieldTypeTraits::MaxType>(closure));
74
75  if (LIKELY(is_dynamic_size_ == false)) {
76    // Write in the extra bytes to store the dynamic size the first time.
77    is_dynamic_size_ = true;
78    size_ += sizeof(Closure::captured_[0].dynamic_.size_);
79  }
80
81  // A closure may be sized dynamically, so always query it for the true size.
82  size_ += closure->GetSize();
83
84  shorty_types_ += ShortyFieldType::kLambda;
85}
86
87size_t ClosureBuilder::GetSize() const {
88  return size_;
89}
90
91size_t ClosureBuilder::GetCaptureCount() const {
92  DCHECK_EQ(values_.size(), shorty_types_.size());
93  return values_.size();
94}
95
96const std::string& ClosureBuilder::GetCapturedVariableShortyTypes() const {
97  DCHECK_EQ(values_.size(), shorty_types_.size());
98  return shorty_types_;
99}
100
101Closure* ClosureBuilder::CreateInPlace(void* memory, ArtLambdaMethod* target_method) const {
102  DCHECK(memory != nullptr);
103  DCHECK(target_method != nullptr);
104  DCHECK_EQ(is_dynamic_size_, target_method->IsDynamicSize());
105
106  CHECK_EQ(target_method->GetNumberOfCapturedVariables(), values_.size())
107    << "number of variables captured at runtime does not match "
108    << "number of variables captured at compile time";
109
110  Closure* closure = new (memory) Closure;
111  closure->lambda_info_ = target_method;
112
113  static_assert(offsetof(Closure, captured_) == kInitialSize, "wrong initial size");
114
115  size_t written_size;
116  if (UNLIKELY(is_dynamic_size_)) {
117    // The closure size must be set dynamically (i.e. nested lambdas).
118    closure->captured_[0].dynamic_.size_ = GetSize();
119    size_t header_size = offsetof(Closure, captured_[0].dynamic_.variables_);
120    DCHECK_LE(header_size, GetSize());
121    size_t variables_size = GetSize() - header_size;
122    written_size =
123        WriteValues(target_method,
124                    closure->captured_[0].dynamic_.variables_,
125                    header_size,
126                    variables_size);
127  } else {
128    // The closure size is known statically (i.e. no nested lambdas).
129    DCHECK(GetSize() == target_method->GetStaticClosureSize());
130    size_t header_size = offsetof(Closure, captured_[0].static_variables_);
131    DCHECK_LE(header_size, GetSize());
132    size_t variables_size = GetSize() - header_size;
133    written_size =
134        WriteValues(target_method,
135                    closure->captured_[0].static_variables_,
136                    header_size,
137                    variables_size);
138  }
139
140  DCHECK_EQ(written_size, closure->GetSize());
141
142  return closure;
143}
144
145size_t ClosureBuilder::WriteValues(ArtLambdaMethod* target_method,
146                                   uint8_t variables[],
147                                   size_t header_size,
148                                   size_t variables_size) const {
149  size_t total_size = header_size;
150  const char* shorty_types = target_method->GetCapturedVariablesShortyTypeDescriptor();
151  DCHECK_STREQ(shorty_types, shorty_types_.c_str());
152
153  size_t variables_offset = 0;
154  size_t remaining_size = variables_size;
155
156  const size_t shorty_count = target_method->GetNumberOfCapturedVariables();
157  DCHECK_EQ(shorty_count, GetCaptureCount());
158
159  for (size_t i = 0; i < shorty_count; ++i) {
160    ShortyFieldType shorty{shorty_types[i]};  // NOLINT [readability/braces] [4]
161
162    size_t var_size;
163    if (LIKELY(shorty.IsStaticSize())) {
164      // TODO: needs more work to support concurrent GC, e.g. read barriers
165      if (kUseReadBarrier == false) {
166        if (UNLIKELY(shorty.IsObject())) {
167          UNIMPLEMENTED(FATAL) << "can't yet safely write objects with read barrier";
168        }
169      } else {
170        if (UNLIKELY(shorty.IsObject())) {
171          UNIMPLEMENTED(FATAL) << "writing objects not yet supported, no GC support";
172        }
173      }
174
175      var_size = shorty.GetStaticSize();
176      DCHECK_LE(var_size, sizeof(values_[i]));
177
178      // Safe even for objects (non-read barrier case) if we never suspend
179      // while the ClosureBuilder is live.
180      // FIXME: Need to add GC support for references in a closure.
181      memcpy(&variables[variables_offset], &values_[i], var_size);
182    } else {
183      DCHECK(shorty.IsLambda())
184          << " don't support writing dynamically sized types other than lambda";
185
186      ShortyFieldTypeTraits::MaxType closure_raw = values_[i];
187      Closure* nested_closure = reinterpret_cast<Closure*>(closure_raw);
188
189      DCHECK(nested_closure != nullptr);
190      nested_closure->CopyTo(&variables[variables_offset], remaining_size);
191
192      var_size = nested_closure->GetSize();
193    }
194
195    total_size += var_size;
196    DCHECK_GE(remaining_size, var_size);
197    remaining_size -= var_size;
198
199    variables_offset += var_size;
200  }
201
202  DCHECK_EQ('\0', shorty_types[shorty_count]);
203  DCHECK_EQ(variables_offset, variables_size);
204
205  return total_size;
206}
207
208
209}  // namespace lambda
210}  // namespace art
211