[WIP] Context API

api/include/opentelemetry/context/context.h

@@ -0,0 +1,168 @@
+#pragma once
+
+#include <atomic>
+#include <iostream>
+#include <map>
+#include <sstream>
+#include <vector>
+
+#include "opentelemetry/common/attribute_value.h"
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/nostd/utility.h"
+#include "opentelemetry/nostd/variant.h"
+#include "opentelemetry/trace/key_value_iterable.h"
+#include "opentelemetry/trace/key_value_iterable_view.h"
+#include "opentelemetry/trace/tracer.h"
+#include "opentelemetry/version.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace context
+{
+
+/* The context class provides a context identifier */
+template <class T>
+class Context
+{
+
+public:
+  /*The Key class is used to obscure access from the
+   * user to the context map. The identifier is used as a key
+   * to the context map.
+   */
+  class Key
+  {
+
+  public:
+    /*Returns the key's identifier*/
+    nostd::string_view GetIdentifier() { return nostd::string_view(identifier_); }
+    /*Returns the key's name */
+    nostd::string_view GetName() { return key_name_; }
+
+  private:
+    friend class Context;
+
+    /* Constructs a new Key with the passed in name. Sets the identifier as
+     * the address of this object. */
+    Key(nostd::string_view key_name) : key_name_{key_name}
+    {
+      std::stringstream ss;
+      ss << (void *)this;
+      nostd::string_view temp_view;
+      temp_view = ss.str();
+
+      memcpy(identifier_, temp_view.data(), temp_view.size());
+    }
+
+    nostd::string_view key_name_;
+
+    char identifier_[50];
+  };
+
+  /* Creates a key with the passed in name and returns it. */
+  Key CreateKey(nostd::string_view key_name) { return Key(key_name); }
+
+  /* Contructor, creates a context object from a map of keys
+   * and identifiers.
+   */
+  Context(const T &attributes) : key_vals_(attributes)
+  {
+    /* Currently only used as a check, to ensure T is of the right type. */
+    trace::KeyValueIterableView<T> iterable = trace::KeyValueIterableView<T>(attributes);
+  }
+
+  Context() {}
+
+  /* Accepts a new iterable and then returns a new  context that
+   * contains both the original pairs and the new pair.
+   */
+  Context WriteValues(T &attributes) noexcept
+  {
+    /* Currently only used as a check, to ensure T is of the right type. */
+    trace::KeyValueIterableView<T> iterable = trace::KeyValueIterableView<T>(attributes);
+
+    std::insert_iterator<T> back(attributes, std::begin(attributes));
+
+    for (auto iter = std::begin(key_vals_); iter != std::end(key_vals_); ++iter)
+    {
+      back = *iter;
+    }
+
+    return Context(attributes);
+  }
+
+  /* Returns the value associated with the passed in key */
+  common::AttributeValue GetValue(Key key)
+  {
+
+    for (auto iter = std::begin(key_vals_); iter != std::end(key_vals_); ++iter)
+    {
+      if (key.GetIdentifier() == iter->first)
+      {
+        return iter->second;
+      }
+    }
+
+    return "";
+  }
+
+  /* Iterates through the current and comparing context objects
+   * to check for equality, */
+  bool operator==(const Context &other)
+  {
+
+    /*Check for case where either both or one object has no contents. */
+    if (std::begin(other.key_vals_) == std::end(other.key_vals_))
+    {
+      if (std::begin(key_vals_) == std::end(key_vals_))
+      {
+        return true;
+      }
+      else
+      {
+        return false;
+      }
+    }
+
+    if (std::begin(key_vals_) == std::end(key_vals_))
+    {
+      return false;
+    }
+
+    /*Compare the contexts*/
+    for (auto iter = std::begin(key_vals_); iter != std::end(key_vals_); ++iter)
+    {
+      int found = 0;
+
+      for (auto iter_other = std::begin(other.key_vals_); iter_other != std::end(other.key_vals_);
+           iter_other++)
+      {
+        if (iter->first == iter_other->first)
+        {
+          if (nostd::get<nostd::string_view>(iter->second) ==
+              nostd::get<nostd::string_view>(iter_other->second))
+          {
+            found = 1;
+            break;
+          }
+        }
+      }
+
+      if (found == 0)
+      {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  /* Copy Constructors. */
+  Context(const Context &other) = default;
+  Context &operator=(const Context &other) = default;
+
+private:
+  T key_vals_;
+};
+
+}  // namespace context
+OPENTELEMETRY_END_NAMESPACE

api/include/opentelemetry/context/runtime_context.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include "context.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace context
+{
+
+/* The RuntimeContext class provides a wrapper for
+ * propogating context through cpp. */
+template <class M>
+class RuntimeContext
+{
+public:
+  /* The token class provides an identifier that is used by
+   * the attach and detach methods to keep track of context
+   * objects.
+   */
+  class Token
+  {
+  private:
+    friend class RuntimeContext<M>;
+
+    Context<M> context_;
+
+    /* A constructor that sets the token's Context object to the
+     * one that was passed in.
+     */
+    Token(Context<M> &context) { context_ = context; }
+
+    /* Returns the stored context object. */
+    Context<M> GetContext() { return context_; }
+  };
+
+  /* Return the current context. */
+  Context<M> GetCurrent();
+
+  /* Sets the current 'Context' object. Returns a token
+   * that can be used to reset to the previous Context.
+   */
+
+  Token Attach(Context<M> &context);
+
+  /* Resets the context to a previous value stored in the
+   * passed in token. Returns zero if successful, -1 otherwise
+   */
+  int Detach(Token &token);
+};
+}  // namespace context
+OPENTELEMETRY_END_NAMESPACE

api/include/opentelemetry/context/threadlocal_context.h

@@ -0,0 +1,73 @@
+#pragma once
+
+#include "opentelemetry/context/runtime_context.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace context
+{
+/* The ThreadLocalContext class is a derived class from RuntimeContext and
+ * provides a wrapper for
+ * propogating context through cpp thread locally. */
+template <class M>
+class ThreadLocalContext : public RuntimeContext<M>
+{
+public:
+  /* The token class provides an identifier that is used by
+   * the attach and detach methods to keep track of context
+   * objects.
+   */
+  class Token
+  {
+  private:
+    friend class ThreadLocalContext<M>;
+
+    Context<M> context_;
+
+    /* A constructor that sets the token's Context object to the
+     * one that was passed in.
+     */
+    Token(Context<M> &context) { context_ = context; }
+
+    /* Returns the stored context object. */
+    Context<M> GetContext() { return context_; }
+  };
+
+  /* Return the current context. */
+  static Context<M> GetCurrent() { return GetInstance(); }
+
+  /* Resets the context to a previous value stored in the
+   * passed in token. Returns zero if successful, -1 otherwise
+   */
+  static int Detach(Token &token)
+  {
+
+    /* If the token context is the current context, return failure. */
+    if (token.GetContext() == GetCurrent())
+    {
+      return 1;
+    }
+
+    GetInstance() = token.GetContext();
+    return 0;
+  }
+
+  /* Sets the current 'Context' object. Returns a token
+   * that can be used to reset to the previous Context.
+   */
+  static Token Attach(Context<M> &context)
+  {
+    Token old_context = Token(GetInstance());
+    GetInstance()     = context;
+    return old_context;
+  }
+
+private:
+  /* Provides storage and access to the thread_local context object */
+  static Context<M> &GetInstance()
+  {
+    static thread_local Context<M> instance;
+    return instance;
+  }
+};
+}  // namespace context
+OPENTELEMETRY_END_NAMESPACE

api/test/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(core)
+add_subdirectory(context)
 add_subdirectory(plugin)
 add_subdirectory(nostd)
 add_subdirectory(trace)

api/test/context/BUILD

@@ -0,0 +1,23 @@
+load("//bazel:otel_cc_benchmark.bzl", "otel_cc_benchmark")
+
+cc_test(
+    name = "context_test",
+    srcs = [
+        "context_test.cc",
+    ],
+    deps = [
+        "//api",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "thread_local_test",
+    srcs = [
+        "thread_local_test.cc",
+    ],
+    deps = [
+        "//api",
+        "@com_google_googletest//:gtest_main",
+    ],
+)