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OpenTelemetry as a single .dll

This branch builds a single .dll, combining both api + sdk parts, instead of being separate .dlls.

Why?

  • The vcpkg version of the package can build only static libraries, and in the future, if dynamic works it'll create .dll for each component: zlib, protobuf, etc.
  • The built-in CMake rules produce more than one .dll, and do not expose all of the sdk by default.

There are some critical issues with OpenTelemetry C++ in the original branch:

  • The static library version does not work across dlls using it - their own singleton_test fails.
  • The static library brings dozen of dependencies (zlib, protobuf, grpc, etc.)
  • This not only increases the distribution size (from 100mb to 2GB), it can also silently introduce ODR violations too.
  • Integration with MSVC's STL is needed, instead of relying the nostd custom implementation (using abseil internally).

Why not CMake:

  • It's not friendly, neither from the command-line, nor from the IDE.
  • It requires plenty of custom build steps, some from the ci/ folder, others from tools/
pwsh ci/setup_windows_ci_environment.ps1
pwsh ci/do_ci.ps1 cmake.dll.test
pwsh ci/do_ci.ps1 cmake.exporter.otprotocol.dll.test

To tackle the above issues, this branch creates a dynamic otel_sdk_r.dll library, exposing only the OpenTelemetry C++ api:

  • All of the api classes are inline, and only few static function members need to be exported, in order to guarantee single stroage for their own static variables ("singletons")
  • Hence OPENTELEMETRY_API_SINGLETON would be __declspec(dllimport) when using the library.
  • For the sdk part (exporters, ext, etc.) the above is not used, but rather OPENTELEMETRY_EXPORT (also dllimport) for some classes.

Build settings

How to use

In order to use the library, the users only need to define OPENTELEMETRY_DLL to 1, and include <opentelemetry/version.h> as the first file:

#define OPENTELEMETRY_DLL 1
#include <opentelemetry/version.h> 
#include <opentelemetry/... some other header file>
  • Some MSVC warnings might have to be disabled too, like: 4505 4251 4275

Some limitations

Some things are missing: - The protobuf level of accessing metrics/logs/trace APIs is missing. - Some useful plumbing with grpc is missing too.

Building

This branch uses bazel to build, and relies on the //:with_dll bool flag to configure the build in dll mode:

bazel test --//:with_dll=true ... -k

This produces otel_sdk_rd.dll (in the default fastbuild configuration, rd stands for release/debug borrowed from CMake's jargon).

Packaging

A single otel_sdk.zip is produced, mimicking how vcpkg exports packages: - Single include/ folder - Three lib folders: lib/, debug/lib and reldeb/lib (vcpkg only generates the first two) - Same for bin: bin, debug/bin and reldeb/bin - In addition Sentry's sentrycli was used to gather (from the .pdb files) all sources used to compile and bundle them in additional .zip files.