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