src/base/CodeContext.cc

   1 /*
   2  * Copyright (C) 1996-2022 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS code_contexts for details.
   7  */
   8
   9 #include "squid.h"
  10 #include "base/CodeContext.h"
  11 #include "Debug.h"
  12
  13 /// represents a being-forgotten CodeContext (while it may be being destroyed)
  14 class FadingCodeContext: public CodeContext
  15 {
  16 public:
  17     /* CodeContext API */
  18     virtual ScopedId codeContextGist() const override { return gist; }
  19     virtual std::ostream &detailCodeContext(std::ostream &os) const override { return os << gist; }
  20
  21     ScopedId gist; ///< identifies the being-forgotten CodeContext
  22 };
  23
  24 /// guarantees the forever existence of the pointer, starting from the first use
  25 static CodeContext::Pointer &
  26 Instance()
  27 {
  28     static const auto Instance = new CodeContext::Pointer(nullptr);
  29     return *Instance;
  30 }
  31
  32 const CodeContext::Pointer &
  33 CodeContext::Current()
  34 {
  35     return Instance();
  36 }
  37
  38 /// Forgets the current known context, possibly triggering its destruction.
  39 /// Preserves the gist of the being-forgotten context during its destruction.
  40 /// Knows nothing about the next context -- the caller must set it.
  41 void
  42 CodeContext::ForgetCurrent()
  43 {
  44     static const RefCount<FadingCodeContext> fadingCodeContext = new FadingCodeContext();
  45     auto &current = Instance();
  46     assert(current);
  47     fadingCodeContext->gist = current->codeContextGist();
  48     current = fadingCodeContext;
  49 }
  50
  51 /// Switches the current context to the given known context. Improves debugging
  52 /// output by replacing omni-directional "Reset" with directional "Entering".
  53 void
  54 CodeContext::Entering(const Pointer &codeCtx)
  55 {
  56     auto &current = Instance();
  57     if (current)
  58         ForgetCurrent(); // ensure orderly closure of the old context
  59     current = codeCtx;
  60     debugs(1, 5, codeCtx->codeContextGist());
  61 }
  62
  63 /// Forgets the current known context. Improves debugging output by replacing
  64 /// omni-directional "Reset" with directional "Leaving".
  65 void
  66 CodeContext::Leaving()
  67 {
  68     ForgetCurrent();
  69     auto &current = Instance();
  70     debugs(1, 7, *current);
  71     current = nullptr;
  72 }
  73
  74 void
  75 CodeContext::Reset()
  76 {
  77     if (Instance())
  78         Leaving();
  79 }
  80
  81 void
  82 CodeContext::Reset(const Pointer codeCtx)
  83 {
  84     if (codeCtx == Current())
  85         return; // context has not actually changed
  86
  87     if (!codeCtx)
  88         return Leaving();
  89
  90     Entering(codeCtx);
  91 }
  92
  93 std::ostream &
  94 CurrentCodeContextDetail(std::ostream &os)
  95 {
  96     if (const auto ctx = CodeContext::Current())
  97         ctx->detailCodeContext(os);
  98     return os;
  99 }
 100