1 // Copyright 2006 Google Inc. All Rights Reserved.
2
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6
7 // http://www.apache.org/licenses/LICENSE-2.0
8
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 // queue.cc : simple thread safe queue implementation
16
17 #include <stdlib.h>
18
19 // This file must work with autoconf on its public version,
20 // so these includes are correct.
21 #include "queue.h"
22 #include "sattypes.h"
23
24 // Page entry queue implementation follows.
25 // Push inserts pages, pop returns a random entry.
26
27
PageEntryQueue(uint64 queuesize)28 PageEntryQueue::PageEntryQueue(uint64 queuesize) {
29 // There must always be one empty queue location,
30 // since in == out => empty.
31 q_size_ = queuesize + 1;
32 pages_ = new struct page_entry[q_size_];
33 nextin_ = 0;
34 nextout_ = 0;
35 popped_ = 0;
36 pushed_ = 0;
37 pthread_mutex_init(&q_mutex_, NULL);
38 }
~PageEntryQueue()39 PageEntryQueue::~PageEntryQueue() {
40 delete[] pages_;
41 pthread_mutex_destroy(&q_mutex_);
42 }
43
44 // Add a page into this queue.
Push(struct page_entry * pe)45 int PageEntryQueue::Push(struct page_entry *pe) {
46 int result = 0;
47 int64 nextnextin;
48
49 if (!pe)
50 return 0;
51
52 pthread_mutex_lock(&q_mutex_);
53 nextnextin = (nextin_ + 1) % q_size_;
54
55 if (nextnextin != nextout_) {
56 pages_[nextin_] = *pe;
57
58 nextin_ = nextnextin;
59 result = 1;
60
61 pushed_++;
62 }
63
64 pthread_mutex_unlock(&q_mutex_);
65
66 return result;
67 }
68
69 // Retrieve a random page from this queue.
PopRandom(struct page_entry * pe)70 int PageEntryQueue::PopRandom(struct page_entry *pe) {
71 int result = 0;
72 int64 lastin;
73 int64 entries;
74 int64 newindex;
75 struct page_entry tmp;
76
77 if (!pe)
78 return 0;
79
80 // TODO(nsanders): we should improve random to get 64 bit randoms, and make
81 // it more thread friendly.
82 uint64 rand = random();
83
84 int retval = pthread_mutex_lock(&q_mutex_);
85 if (retval)
86 logprintf(0, "Process Error: pthreads mutex failure %d\n", retval);
87
88
89 if (nextin_ != nextout_) {
90 // Randomized fetch.
91 // Swap random entry with next out.
92 {
93 lastin = (nextin_ - 1 + q_size_) % q_size_;
94 entries = (lastin - nextout_ + q_size_) % q_size_;
95
96 newindex = nextout_;
97 if (entries)
98 newindex = ((rand % entries) + nextout_) % q_size_;
99
100 // Swap the pages.
101 tmp = pages_[nextout_];
102 pages_[nextout_] = pages_[newindex];
103 pages_[newindex] = tmp;
104 }
105
106 // Return next out page.
107 *pe = pages_[nextout_];
108
109 nextout_ = (nextout_ + 1) % q_size_;
110 result = 1;
111
112 popped_++;
113 }
114
115 pthread_mutex_unlock(&q_mutex_);
116
117 return result;
118 }
119