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135 lines
6.3 KiB
C++
135 lines
6.3 KiB
C++
/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
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// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
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#ident "$Id$"
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/*======
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This file is part of PerconaFT.
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Copyright (c) 2006, 2015, Percona and/or its affiliates. All rights reserved.
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PerconaFT is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License, version 2,
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as published by the Free Software Foundation.
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PerconaFT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with PerconaFT. If not, see <http://www.gnu.org/licenses/>.
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----------------------------------------
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PerconaFT is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License, version 3,
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as published by the Free Software Foundation.
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PerconaFT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with PerconaFT. If not, see <http://www.gnu.org/licenses/>.
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======= */
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#ident "Copyright (c) 2006, 2015, Percona and/or its affiliates. All rights reserved."
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#pragma once
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// Overview: A partitioned_counter provides a counter that can be incremented and the running sum can be read at any time.
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// We assume that increments are frequent, whereas reading is infrequent.
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// Implementation hint: Use thread-local storage so each thread increments its own data. The increment does not require a lock or atomic operation.
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// Reading the data can be performed by iterating over the thread-local versions, summing them up.
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// The data structure also includes a sum for all the threads that have died.
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// Use a pthread_key to create the thread-local versions. When a thread finishes, the system calls pthread_key destructor which can add that thread's copy
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// into the sum_of_dead counter.
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// Rationale: For statistics such as are found in engine status, we need a counter that requires no cache misses to increment. We've seen significant
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// performance speedups by removing certain counters. Rather than removing those statistics, we would like to just make the counter fast.
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// We generally increment the counters frequently, and want to fetch the values infrequently.
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// The counters are monotonic.
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// The counters can be split into many counters, which can be summed up at the end.
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// We don't care if we get slightly out-of-date counter sums when we read the counter. We don't care if there is a race on reading the a counter
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// variable and incrementing.
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// See tests/test_partitioned_counter.c for some performance measurements.
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// Operations:
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// create_partitioned_counter Create a counter initialized to zero.
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// destroy_partitioned_counter Destroy it.
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// increment_partitioned_counter Increment it. This is the frequent operation.
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// read_partitioned_counter Get the current value. This is infrequent.
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// See partitioned_counter.cc for the abstraction function and representation invariant.
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//
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// The google style guide says to avoid using constructors, and it appears that
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// constructors may have broken all the tests, because they called
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// pthread_key_create before the key was actually created. So the google style
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// guide may have some wisdom there...
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//
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// This version does not use constructors, essentially reverrting to the google C++ style guide.
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//
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// The old C interface. This required a bunch of explicit ___attribute__((__destructor__)) functions to remember to destroy counters at the end.
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#if defined(__cplusplus)
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extern "C" {
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#endif
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typedef struct partitioned_counter *PARTITIONED_COUNTER;
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PARTITIONED_COUNTER create_partitioned_counter(void);
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// Effect: Create a counter, initialized to zero.
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void destroy_partitioned_counter(PARTITIONED_COUNTER);
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// Effect: Destroy the counter. No operations on that counter are permitted after this.
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void increment_partitioned_counter(PARTITIONED_COUNTER, uint64_t amount);
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// Effect: Increment the counter by amount.
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// Requires: No overflows. This is a 64-bit unsigned counter.
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uint64_t read_partitioned_counter(PARTITIONED_COUNTER) __attribute__((__visibility__("default")));
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// Effect: Return the current value of the counter.
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void partitioned_counters_init(void);
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// Effect: Initialize any partitioned counters data structures that must be set up before any partitioned counters run.
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void partitioned_counters_destroy(void);
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// Effect: Destroy any partitioned counters data structures.
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#if defined(__cplusplus)
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};
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#endif
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#if 0
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#include <pthread.h>
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#include "fttypes.h"
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// Used inside the PARTITIONED_COUNTER.
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struct linked_list_head {
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struct linked_list_element *first;
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};
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class PARTITIONED_COUNTER {
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public:
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PARTITIONED_COUNTER(void);
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// Effect: Construct a counter, initialized to zero.
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~PARTITIONED_COUNTER(void);
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// Effect: Destruct the counter.
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void increment(uint64_t amount);
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// Effect: Increment the counter by amount. This is a 64-bit unsigned counter, and if you overflow it, you will get overflowed results (that is mod 2^64).
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// Requires: Don't use this from a static constructor or destructor.
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uint64_t read(void);
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// Effect: Read the sum.
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// Requires: Don't use this from a static constructor or destructor.
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private:
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uint64_t _sum_of_dead; // The sum of all thread-local counts from threads that have terminated.
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pthread_key_t _key; // The pthread_key which gives us the hook to construct and destruct thread-local storage.
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struct linked_list_head _ll_counter_head; // A linked list of all the thread-local information for this counter.
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// This function is used to destroy the thread-local part of the state when a thread terminates.
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// But it's not the destructor for the local part of the counter, it's a destructor on a "dummy" key just so that we get a notification when a thread ends.
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friend void destroy_thread_local_part_of_partitioned_counters (void *);
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};
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#endif
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