libphobos/libdruntime/core/volatile.d

   1 /**
   2  * This module declares intrinsics for volatile operations.
   3  *
   4  * Copyright: Copyright © 2019, The D Language Foundation
   5  * License:   $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
   6  * Authors:   Walter Bright, Ernesto Castellotti
   7  * Source:    $(DRUNTIMESRC core/volatile.d)
   8  */
   9
  10 module core.volatile;
  11
  12 nothrow:
  13 @safe:
  14 @nogc:
  15
  16 /*************************************
  17  * Read/write value from/to the memory location indicated by ptr.
  18  *
  19  * These functions are recognized by the compiler, and calls to them are guaranteed
  20  * to not be removed (as dead assignment elimination or presumed to have no effect)
  21  * or reordered in the same thread.
  22  *
  23  * These reordering guarantees are only made with regards to other
  24  * operations done through these functions; the compiler is free to reorder regular
  25  * loads/stores with regards to loads/stores done through these functions.
  26  *
  27  * This is useful when dealing with memory-mapped I/O (MMIO) where a store can
  28  * have an effect other than just writing a value, or where sequential loads
  29  * with no intervening stores can retrieve
  30  * different values from the same location due to external stores to the location.
  31  *
  32  * These functions will, when possible, do the load/store as a single operation. In
  33  * general, this is possible when the size of the operation is less than or equal to
  34  * $(D (void*).sizeof), although some targets may support larger operations. If the
  35  * load/store cannot be done as a single operation, multiple smaller operations will be used.
  36  *
  37  * These are not to be conflated with atomic operations. They do not guarantee any
  38  * atomicity. This may be provided by coincidence as a result of the instructions
  39  * used on the target, but this should not be relied on for portable programs.
  40  * Further, no memory fences are implied by these functions.
  41  * They should not be used for communication between threads.
  42  * They may be used to guarantee a write or read cycle occurs at a specified address.
  43  */
  44
  45 ubyte  volatileLoad(ubyte * ptr);
  46 ushort volatileLoad(ushort* ptr);  /// ditto
  47 uint   volatileLoad(uint  * ptr);  /// ditto
  48 ulong  volatileLoad(ulong * ptr);  /// ditto
  49
  50 void volatileStore(ubyte * ptr, ubyte  value);   /// ditto
  51 void volatileStore(ushort* ptr, ushort value);   /// ditto
  52 void volatileStore(uint  * ptr, uint   value);   /// ditto
  53 void volatileStore(ulong * ptr, ulong  value);   /// ditto
  54
  55 @system unittest
  56 {
  57     alias TT(T...) = T;
  58
  59     foreach (T; TT!(ubyte, ushort, uint, ulong))
  60     {
  61         T u;
  62         T* p = &u;
  63         volatileStore(p, 1);
  64         T r = volatileLoad(p);
  65         assert(r == u);
  66     }
  67 }