forked from mirrors/0ad
janwas
c3a42633fa
also improved filtering of the frame delta times. while at it, improved interface of whrt backends to avoid leaking implementation details. This was SVN commit r6401.
100 lines
3.0 KiB
C++
100 lines
3.0 KiB
C++
/**
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* =========================================================================
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* File : counter.cpp
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* Project : 0 A.D.
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* Description : Interface for counter implementations
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#include "precompiled.h"
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#include "counter.h"
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#include "lib/bits.h"
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#include "lib/sysdep/cpu.h" // cpu_CAS
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#include "tsc.h"
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#include "hpet.h"
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#include "pmt.h"
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#include "qpc.h"
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#include "tgt.h"
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// to add a new counter type, simply include its header here and
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// insert a case in ConstructCounterAt's switch statement.
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//-----------------------------------------------------------------------------
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// create/destroy counters
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/**
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* @return pointer to a newly constructed ICounter subclass of type <id> at
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* the given address, or 0 iff the ID is invalid.
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* @param size maximum allowable size [bytes] of the subclass instance
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**/
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static ICounter* ConstructCounterAt(size_t id, void* address, size_t size)
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{
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// rationale for placement new: see call site.
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// counters are chosen according to the following order. rationale:
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// - TSC must come before QPC and PMT to make sure a bug in the latter on
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// Pentium systems doesn't come up.
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// - PMT works, but is inexplicably slower than QPC on a PIII Mobile.
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// - TGT really isn't as safe as the others, so it should be last.
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// - low-overhead and high-resolution counters are preferred.
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switch(id)
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{
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case 0:
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return CreateCounterHPET(address, size);
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case 1:
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return CreateCounterTSC(address, size);
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case 2:
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return CreateCounterQPC(address, size);
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case 3:
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return CreateCounterPMT(address, size);
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case 4:
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return CreateCounterTGT(address, size);
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default:
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return 0;
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}
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}
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static volatile uintptr_t isCounterAllocated;
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ICounter* CreateCounter(size_t id)
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{
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// we placement-new the Counter classes in a static buffer.
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// this is dangerous, but we are careful to ensure alignment. it is
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// unusual and thus bad, but there's also one advantage: we avoid
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// using global operator new before the CRT is initialized (risky).
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//
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// alternatives:
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// - defining as static doesn't work because the ctors (necessary for
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// vptr initialization) run during _cinit, which comes after our
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// first use of them.
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// - using static_calloc isn't possible because we don't know the
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// size until after the alloc / placement new.
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if(!cpu_CAS(&isCounterAllocated, 0, 1))
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debug_assert(0); // static counter memory is already in use!
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static const size_t memSize = 200;
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static u8 mem[memSize];
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u8* alignedMem = (u8*)round_up((uintptr_t)mem, (uintptr_t)16u);
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const size_t bytesLeft = mem+memSize - alignedMem;
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ICounter* counter = ConstructCounterAt(id, alignedMem, bytesLeft);
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return counter;
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}
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void DestroyCounter(ICounter*& counter)
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{
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debug_assert(counter);
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counter->Shutdown();
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counter->~ICounter(); // must be called due to placement new
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counter = 0;
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isCounterAllocated = 0;
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}
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