// Copyright 2006 Google Inc. All Rights Reserved.
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// queue.cc : simple thread safe queue implementation
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#include <stdlib.h>
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// This file must work with autoconf on its public version,
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// so these includes are correct.
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#include "queue.h"
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#include "sattypes.h"
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// Page entry queue implementation follows.
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// Push inserts pages, pop returns a random entry.
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PageEntryQueue::PageEntryQueue(uint64 queuesize) {
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// There must always be one empty queue location,
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// since in == out => empty.
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q_size_ = queuesize + 1;
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pages_ = new struct page_entry[q_size_];
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nextin_ = 0;
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nextout_ = 0;
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popped_ = 0;
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pushed_ = 0;
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pthread_mutex_init(&q_mutex_, NULL);
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}
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PageEntryQueue::~PageEntryQueue() {
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delete[] pages_;
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pthread_mutex_destroy(&q_mutex_);
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}
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// Add a page into this queue.
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int PageEntryQueue::Push(struct page_entry *pe) {
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int result = 0;
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int64 nextnextin;
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if (!pe)
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return 0;
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pthread_mutex_lock(&q_mutex_);
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nextnextin = (nextin_ + 1) % q_size_;
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if (nextnextin != nextout_) {
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pages_[nextin_] = *pe;
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nextin_ = nextnextin;
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result = 1;
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pushed_++;
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}
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pthread_mutex_unlock(&q_mutex_);
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return result;
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}
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// Retrieve a random page from this queue.
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int PageEntryQueue::PopRandom(struct page_entry *pe) {
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int result = 0;
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int64 lastin;
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int64 entries;
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int64 newindex;
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struct page_entry tmp;
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if (!pe)
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return 0;
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// TODO(nsanders): we should improve random to get 64 bit randoms, and make
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// it more thread friendly.
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uint64 rand = random();
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int retval = pthread_mutex_lock(&q_mutex_);
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if (retval)
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logprintf(0, "Process Error: pthreads mutex failure %d\n", retval);
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if (nextin_ != nextout_) {
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// Randomized fetch.
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// Swap random entry with next out.
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{
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lastin = (nextin_ - 1 + q_size_) % q_size_;
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entries = (lastin - nextout_ + q_size_) % q_size_;
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newindex = nextout_;
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if (entries)
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newindex = ((rand % entries) + nextout_) % q_size_;
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// Swap the pages.
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tmp = pages_[nextout_];
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pages_[nextout_] = pages_[newindex];
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pages_[newindex] = tmp;
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}
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// Return next out page.
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*pe = pages_[nextout_];
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nextout_ = (nextout_ + 1) % q_size_;
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result = 1;
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popped_++;
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}
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pthread_mutex_unlock(&q_mutex_);
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return result;
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}
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