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Commitde6429a

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Provide a generic fallback for pg_compiler_barrier using an extern function.
If the compiler/arch combination does not provide compiler barriers,provide a fallback. That fallback simply consists out of a functioncall into a externally defined function. That should guaranteecompiler barrierer semantics except for compilers that do intertranslation unit/global optimization - those better provide an actualcompiler barrier.Hopefully this fixes Tom's report of linker failures due topg_compiler_barrier_impl not being provided.I'm not backpatching this commit as it builds on the new atomicsinfrastructure. If we decide an equivalent fix needs to bebackpatched, I'll do so in a separate commit.Discussion: 27746.1420930690@sss.pgh.pa.usPer report from Tom Lane.
1 parentdb4ec2f commitde6429a

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‎src/backend/port/atomics.c

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@@ -32,6 +32,14 @@ pg_spinlock_barrier(void)
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}
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#endif
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#ifdefPG_HAVE_COMPILER_BARRIER_EMULATION
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void
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pg_extern_compiler_barrier(void)
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{
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/* do nothing */
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}
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#endif
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#ifdefPG_HAVE_ATOMIC_FLAG_SIMULATION
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‎src/include/port/atomics/fallback.h

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@@ -35,6 +35,22 @@ extern void pg_spinlock_barrier(void);
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#definepg_memory_barrier_impl pg_spinlock_barrier
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#endif
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#ifndefpg_compiler_barrier_impl
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/*
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* If the compiler/arch combination does not provide compiler barriers,
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* provide a fallback. That fallback simply consists out of a function call
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* into a externally defined function. That should guarantee compiler barrier
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* semantics except for compilers that do inter translation unit/global
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* optimization - those better provide an actual compiler barrier.
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*
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* Using a native compiler barrier for sure is a lot faster than this...
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*/
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#definePG_HAVE_COMPILER_BARRIER_EMULATION
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externvoidpg_extern_compiler_barrier(void);
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#definepg_compiler_barrier_impl pg_extern_compiler_barrier
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#endif
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/*
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* If we have atomics implementation for this platform fall back to providing
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* the atomics API using a spinlock to protect the internal state. Possibly

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