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79 lines
2.7 KiB
C++
79 lines
2.7 KiB
C++
#pragma once
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#include <cstdint>
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#include <atomic>
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namespace DB
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{
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/** Allows to randomize thread scheduling and insert various glitches across whole program for testing purposes.
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* It is done by setting up a timer that will send PROF signal to every thread when certain amount of CPU time has passed.
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*
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* To initialize ThreadFuzzer, call ThreadFuzzer::instance().
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* The behaviour is controlled by environment variables:
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*
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* THREAD_FUZZER_CPU_TIME_PERIOD_US - period of signals in microseconds.
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* THREAD_FUZZER_YIELD_PROBABILITY - probability to do 'sched_yield'.
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* THREAD_FUZZER_MIGRATE_PROBABILITY - probability to set CPU affinity to random CPU core.
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* THREAD_FUZZER_SLEEP_PROBABILITY - probability to sleep.
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* THREAD_FUZZER_SLEEP_TIME_US - amount of time to sleep in microseconds.
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*
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* ThreadFuzzer will do nothing if environment variables are not set accordingly.
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*
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* The intention is to reproduce thread synchronization bugs (race conditions and deadlocks) more frequently in tests.
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* We already have tests with TSan. But TSan only covers "physical" synchronization bugs, but not "logical" ones,
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* where all data is protected by synchronization primitives, but we still have race conditions.
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* Obviously, TSan cannot debug distributed synchronization bugs.
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*
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* The motivation for this tool is an evidence, that concurrency bugs are more likely to reproduce
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* on bad unstable virtual machines in a dirty environments.
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*
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* The idea is not new, see also:
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* https://channel9.msdn.com/blogs/peli/concurrency-fuzzing-with-cuzz
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*
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* Notes:
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* - it can be also implemented with instrumentation (example: LLVM Xray) instead of signals.
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* - we should also make the sleep time random.
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* - sleep and migration obviously helps, but the effect of yield is unclear.
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*
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* In addition, we allow to inject glitches around thread synchronization functions.
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* Example:
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*
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* THREAD_FUZZER_pthread_mutex_lock_BEFORE_SLEEP_PROBABILITY=0.001
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* THREAD_FUZZER_pthread_mutex_lock_BEFORE_SLEEP_TIME_US=10000
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* THREAD_FUZZER_pthread_mutex_lock_AFTER_SLEEP_PROBABILITY=0.001
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* THREAD_FUZZER_pthread_mutex_lock_AFTER_SLEEP_TIME_US=10000
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*/
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class ThreadFuzzer
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{
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public:
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static ThreadFuzzer & instance()
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{
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static ThreadFuzzer res;
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return res;
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}
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bool isEffective() const;
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static void stop();
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static void start();
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static bool isStarted();
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private:
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uint64_t cpu_time_period_us = 0;
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double yield_probability = 0;
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double migrate_probability = 0;
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double sleep_probability = 0;
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double sleep_time_us = 0;
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inline static std::atomic<bool> started{true};
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ThreadFuzzer();
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void initConfiguration();
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void setup() const;
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static void signalHandler(int);
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};
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}
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