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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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