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92 lines
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<!--*********************************************************************--> |
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<h1><atomic> design</h1> |
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<!--*********************************************************************--> |
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<p> |
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There are currently 3 designs under consideration. They differ in where most |
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of the implementation work is done. The functionality exposed to the customer |
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should be identical (and conforming) for all three designs. |
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<ol type="A"> |
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<a href="atomic_design_a.html">Minimal work for the library</a> |
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<li> |
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<a href="atomic_design_b.html">Something in between</a> |
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<a href="atomic_design_c.html">Minimal work for the front end</a> |
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With any design, the (back end) compiler writer should note: |
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<blockquote> |
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<p> |
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The decision to implement lock-free operations on any given type (or not) is an |
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ABI-binding decision. One can not change from treating a type as not lock free, |
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to lock free (or vice-versa) without breaking your ABI. |
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</p> |
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<p> |
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Example: |
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</p> |
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<blockquote><pre> |
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TU1.cc |
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----------- |
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extern atomic<long long> A; |
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int foo() { return A.compare_exchange_strong(w, x); } |
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TU2.cc |
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----------- |
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extern atomic<long long> A; |
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void bar() { return A.compare_exchange_strong(y, z); } |
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</pre></blockquote> |
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</blockquote> |
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<p> |
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If only <em>one</em> of these calls to <tt>compare_exchange_strong</tt> is |
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implemented with mutex-locked code, then that mutex-locked code will not be |
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executed mutually exclusively of the one implemented in a lock-free manner. |
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