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Add templated utility class to centralize common pattern
All reading code has a (for threaded reads) need to maintain a set of contexts and re-use them while dispatching N threads. Create a class to do that and remove duplicate code. This also lowers the scope of when the contexts are alive to reduce memory bloat Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>
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| // | ||
| // SPDX-License-Identifier: BSD-3-Clause | ||
| // Copyright (c) Contributors to the OpenEXR Project. | ||
| // | ||
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| #ifndef INCLUDED_ILM_THREAD_PROCESS_GROUP_H | ||
| #define INCLUDED_ILM_THREAD_PROCESS_GROUP_H | ||
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| //----------------------------------------------------------------------------- | ||
| // | ||
| // Class ProcessGroup is a templated inline helper for constraining | ||
| // task contexts to a number of threads. It maintains a list of | ||
| // contexts and then can hand them out one at a time, waiting for a | ||
| // previous thread request to finish before handing out more, | ||
| // preventing over-subscription / allocation of contexts. | ||
| // | ||
| //----------------------------------------------------------------------------- | ||
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| #include "IlmThreadConfig.h" | ||
| #include "IlmThreadExport.h" | ||
| #include "IlmThreadNamespace.h" | ||
| #include "IlmThreadSemaphore.h" | ||
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| #include "Iex.h" | ||
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| #include <atomic> | ||
| #include <string> | ||
| #include <type_traits> | ||
| #include <vector> | ||
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| ILMTHREAD_INTERNAL_NAMESPACE_HEADER_ENTER | ||
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| template <typename P, | ||
| std::enable_if_t < | ||
| std::is_default_constructible <P>::value && | ||
| std::is_same <decltype (P {}.next), P *>::value, bool> = true> | ||
| class ProcessGroup | ||
| { | ||
| public: | ||
| using Process = P; | ||
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| ProcessGroup (unsigned int numThreads) | ||
| : _sem (numThreads) | ||
| , _avail_head (nullptr) | ||
| , _first_failure (nullptr) | ||
| { | ||
| _fixed_pool.resize (numThreads); | ||
| for ( unsigned int i = 0; i < numThreads; ++i ) | ||
| { | ||
| if (i == (numThreads - 1)) | ||
| _fixed_pool[i].next = nullptr; | ||
| else | ||
| _fixed_pool[i].next = &(_fixed_pool[i+1]); | ||
| } | ||
| _avail_head = &(_fixed_pool[0]); | ||
| } | ||
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| ProcessGroup (const ProcessGroup&) = delete; | ||
| ProcessGroup& operator= (const ProcessGroup&) = delete; | ||
| ProcessGroup (ProcessGroup&&) = default; | ||
| ProcessGroup& operator= (ProcessGroup&&) = delete; | ||
| ~ProcessGroup() | ||
| { | ||
| std::string *cur = _first_failure.load (); | ||
| delete cur; | ||
| } | ||
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| void push (Process *p) | ||
| { | ||
| Process* oldhead = _avail_head.load (std::memory_order_relaxed); | ||
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| do | ||
| { | ||
| p->next = oldhead; | ||
| } while (!_avail_head.compare_exchange_weak ( | ||
| oldhead, p, | ||
| std::memory_order_release, | ||
| std::memory_order_relaxed)); | ||
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| // notify someone else there's one available | ||
| _sem.post (); | ||
| } | ||
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| // called by the thread dispatching work units, may block | ||
| Process* pop () | ||
| { | ||
| Process* ret = nullptr; | ||
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| // we do not have to worry about ABA problems as | ||
| // we have a static pool of items we own, we're just | ||
| // putting them here and popping them off. | ||
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| // used for honoring the numThreads, as pop | ||
| // should only be called by the one thread | ||
| // waiting to submit thread calls | ||
| _sem.wait (); | ||
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| ret = _avail_head.load (std::memory_order_acquire); | ||
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| Process* newhead; | ||
| do | ||
| { | ||
| if (!ret) | ||
| std::cerr << "GACK: serious failure case???" << std::endl; | ||
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| newhead = ret->next; | ||
| } while ( !_avail_head.compare_exchange_weak( | ||
| ret, newhead, std::memory_order_acquire)); | ||
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| return ret; | ||
| } | ||
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| void record_failure (const char *e) | ||
| { | ||
| // should we construct a list of failures if there are | ||
| // more than one? seems less confusing to just report | ||
| // the first we happened to record | ||
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| std::string *cur = _first_failure.load (); | ||
| if (!cur) | ||
| { | ||
| std::string *msg = new std::string (e); | ||
| if (! _first_failure.compare_exchange_strong (cur, msg)) | ||
| delete msg; | ||
| } | ||
| } | ||
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| void throw_on_failure () | ||
| { | ||
| std::string *cur = _first_failure.load (); | ||
| _first_failure.store (nullptr); | ||
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| if (cur) | ||
| { | ||
| std::string msg (*cur); | ||
| delete cur; | ||
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| throw IEX_NAMESPACE::IoExc (msg); | ||
| } | ||
| } | ||
| private: | ||
| Semaphore _sem; | ||
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| std::vector<Process> _fixed_pool; | ||
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| std::atomic<Process *> _avail_head; | ||
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| std::atomic<std::string *> _first_failure; | ||
| }; | ||
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| ILMTHREAD_INTERNAL_NAMESPACE_HEADER_EXIT | ||
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| #endif // INCLUDED_ILM_THREAD_POOL_H |
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