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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 // DnsQueue is implemented as an almost FIFO circular buffer for text | 5 // DnsQueue is implemented as an almost FIFO circular buffer for text |
6 // strings that don't have embedded nulls ('\0'). The "almost" element is that | 6 // strings that don't have embedded nulls ('\0'). The "almost" element is that |
7 // some duplicate strings may be removed (i.e., the string won't really be | 7 // some duplicate strings may be removed (i.e., the string won't really be |
8 // pushed *if* the class happens to notice that a duplicate is already in the | 8 // pushed *if* the class happens to notice that a duplicate is already in the |
9 // queue). | 9 // queue). |
10 // The buffers internal format is null terminated character strings | 10 // The buffers internal format is null terminated character strings |
11 // (a.k.a., c_strings). | 11 // (a.k.a., c_strings). |
12 // It is written to be as fast as possible during push() operations, so | 12 // It is written to be as fast as possible during push() operations, so |
13 // that there will be minimal performance impact on a supplier thread. | 13 // that there will be minimal performance impact on a supplier thread. |
14 // The push() operation will not block, and no memory allocation is involved | 14 // The push() operation will not block, and no memory allocation is involved |
15 // (internally) during the push operations. | 15 // (internally) during the push operations. |
16 // The one caveat is that if there is insufficient space in the buffer to | 16 // The one caveat is that if there is insufficient space in the buffer to |
17 // accept additional string via a push(), then the push() will fail, and | 17 // accept additional string via a push(), then the push() will fail, and |
18 // the buffer will be unmodified. | 18 // the buffer will be unmodified. |
19 | 19 |
20 // This class was designed for use in DNS prefetch operations. During | 20 // This class was designed for use in DNS prefetch operations. During |
21 // rendering, the supplier is the renderer (typically), and the consumer | 21 // rendering, the supplier is the renderer (typically), and the consumer |
22 // is a thread that sends messages to an async DNS resolver. | 22 // is a thread that sends messages to an async DNS resolver. |
23 | 23 |
24 #ifndef COMPONENTS_DNS_PREFETCH_RENDERER_PREDICTOR_QUEUE_H__ | 24 #ifndef COMPONENTS_NETWORK_HINTS_RENDERER_DNS_PREFETCH_QUEUE_H__ |
25 #define COMPONENTS_DNS_PREFETCH_RENDERER_PREDICTOR_QUEUE_H__ | 25 #define COMPONENTS_NETWORK_HINTS_RENDERER_DNS_PREFETCH_QUEUE_H__ |
26 | 26 |
27 #include <string> | 27 #include <string> |
28 | 28 |
29 #include "base/basictypes.h" | 29 #include "base/basictypes.h" |
30 #include "base/memory/scoped_ptr.h" | 30 #include "base/memory/scoped_ptr.h" |
31 | 31 |
32 namespace dns_prefetch { | 32 namespace network_hints { |
33 | 33 |
| 34 // A queue of DNS lookup requests for internal use within the network_hints |
| 35 // component. |
34 class DnsQueue { | 36 class DnsQueue { |
35 public: | 37 public: |
36 // BufferSize is a signed type used for indexing into a buffer. | 38 // BufferSize is a signed type used for indexing into a buffer. |
37 typedef int32 BufferSize; | 39 typedef int32 BufferSize; |
38 | 40 |
39 enum PushResult { SUCCESSFUL_PUSH, OVERFLOW_PUSH, REDUNDANT_PUSH }; | 41 enum PushResult { SUCCESSFUL_PUSH, OVERFLOW_PUSH, REDUNDANT_PUSH }; |
40 | 42 |
41 // The size specified in the constructor creates a buffer large enough | 43 // The size specified in the constructor creates a buffer large enough |
42 // to hold at most one string of that length, or "many" | 44 // to hold at most one string of that length, or "many" |
43 // strings of considerably shorter length. Note that strings | 45 // strings of considerably shorter length. Note that strings |
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79 // If writable_ == readable_, then the buffer is empty. | 81 // If writable_ == readable_, then the buffer is empty. |
80 BufferSize readable_; // Next readable char in buffer_. | 82 BufferSize readable_; // Next readable char in buffer_. |
81 BufferSize writeable_; // The next space in buffer_ to push. | 83 BufferSize writeable_; // The next space in buffer_ to push. |
82 | 84 |
83 // Number of queued strings | 85 // Number of queued strings |
84 size_t size_; | 86 size_t size_; |
85 | 87 |
86 DISALLOW_COPY_AND_ASSIGN(DnsQueue); | 88 DISALLOW_COPY_AND_ASSIGN(DnsQueue); |
87 }; // class DnsQueue | 89 }; // class DnsQueue |
88 | 90 |
89 } // namespace dns_prefetch | 91 } // namespace network_hints |
90 | 92 |
91 #endif // COMPONENTS_DNS_PREFETCH_RENDERER_PREDICTOR_QUEUE_H__ | 93 #endif // COMPONENTS_NETWORK_HINTS_RENDERER_DNS_PREFETCH_QUEUE_H__ |
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