Scope should be default constructable

[VivekSubr]

Is your feature request related to a problem?
Wrapping a span in a class so that'll be a global object necessitates keeping track of scopes as members... but making a scope as a member variable is difficult as it is not default constructible.

Describe the solution you'd like
Make Scope default constructible, ie add 'Scope() = default' to the class.

[lalitb]

Scope need to be associated with a Span during it's construction. It doesn't make sense to have the default constructor for it. Can you share an example what you are trying to achieve?

[sirzooro]

I logged similar issue in the past, with possible workaround: #1298

[VivekSubr]

@sirzooro - thank you, I just added the default constructor and recompiled.

@lalitb - Let's say we are wrapping an global 'active span' for a application within a class, and provide a startSpan api, which sets the ActiveSpan in trace::tracer as well,

 m_currentSpan  = m_tracer->StartSpan(spanName);
 m_tracer->WithActiveSpan(m_currentSpan);

We need to keep track of the scopes as well, but scope can't be made a member variable since it's not default constructible.

[VivekSubr]

@lalitb - unfortunately, default constructed Scopes crash!

(gdb) bt
#0 0x00000000004961e9 in opentelemetry::v1::context::RuntimeContext::Detach (token=...)
at /usr/include/opentelemetry/context/runtime_context.h:99
#1 0x0000000000496189 in opentelemetry::v1::context::Token::~Token (this=0x9018c0)
at /usr/include/opentelemetry/context/runtime_context.h:183
#2 0x000000000049615a in opentelemetry::v1::nostd::unique_ptropentelemetry::v1::context::Token::delete_ptr (this=0x9004a0)
at /usr/include/opentelemetry/nostd/unique_ptr.h:133
#3 0x000000000049611b in opentelemetry::v1::nostd::unique_ptropentelemetry::v1::context::Token::reset (this=0x9004a0, ptr=0x0)
at /usr/include/opentelemetry/nostd/unique_ptr.h:108
#4 0x00000000004960e9 in opentelemetry::v1::nostd::unique_ptropentelemetry::v1::context::Token::~unique_ptr (this=0x9004a0)
at /usr/include/opentelemetry/nostd/unique_ptr.h:64
#5 0x00000000004960c5 in opentelemetry::v1::trace::Scope::~Scope (this=0x9004a0) at /usr/include/opentelemetry/trace/scope.h:20

Any idea how I can fix this??

[sirzooro]

@sirzooro - thank you, I just added the default constructor and recompiled.

I mentioned different solution in that issue - use unique_ptr to store Scope object. It looks that implicit move constructor works fine. Here is code snipped copied from that issue

std::unique_ptr<opentelemetry::trace::Scope> scope;
if (...)
    scope = std::unique_ptr<opentelemetry::trace::Scope>(new opentelemetry::trace::Scope(tracer->WithActiveSpan(span)));

[VivekSubr]

@sirzooro - that doesn't help... still get the destructor crash as above.

[sirzooro]

@VivekSubr maybe that default constructor which you added breaks something? I use Scope move constructor when I put it into unique_ptr like in code above, and this works fine for me.

[VivekSubr]

@sirzooro - Crash happened without the default constructor... I have a deque as a member variable of a wrapper class, and it crashes with the above trace on destruction of the wrapper class.

Commenting out the 'Detach' in Token destructor makes this crash go away.

[VivekSubr]

@lalitb / @sirzooro - additional info, it only happens if the wrapper class is static (in my case, singleton).

So, default contructed scope (either by adding the constructor or by sirzooro's move constructor way), and the context being static triggers this crash.

[lalitb]

@VivekSubr - Sorry, I haven't been following up with this issue. Is this issue still relevant ?

[lalitb]

Closing. please reopen if the issue is still relevant.