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https://issues.apache.org/jira/browse/HTRACE-169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14539306#comment-14539306
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Colin Patrick McCabe commented on HTRACE-169:
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So there are two main ways we could support calling custom span receiver code:
1. Have {{libhtrace.so}} use {{dlopen}} and {{dlsym}} to call into
user-supplied code.
2. Have {{libhtrace.so}} invoke a callback function supplied by the program
itself.
The advantage of #1 is that the custom span receiver can be used without any
code changes. However, for practicality reasons, the functions invoked this
way will probably have to have C linkage rather than C\+\+. The way C\+\+
compilers do name mangling is implementation-defined and there can be problems
using a library compiled with version X of some compiler with a span receiver
library compiled with version X + 1 of that compiler. Of course, the developer
could always write an "extern C" function and have that turn around and call a
C++ function as its only action.
Approach #2 doesn't have that drawback (we can provide a reasonable C\+\+
wrapper for our callbacks), but it does require some modification of the client
program. Approach #2 also avoids a dependency on {{libdl.so}} -- but this is a
pretty trivial or nonexistent advantage, since libdl is supplied with the
operating system and has sane versioning and ABI.
No matter whether we go with approach #1 or #2, I think the best way to handle
this is to have a user-defined function that takes a pointer to an opaque
{{htrace_span}} object, and have a stable API for accessing fields within that
object (without disclosing the internal representation). We should also have a
nice C++ wrapper class in {{htrace.hpp}} like with our other APIs.
We probably also want a span receiver close callback. This is useful for
things like short-lived C programs (like simple command line utilities that do
something and then terminate). These programs will probably want to free the
{{htracer}} object before shutting down to ensure that all the spans generated
by the command-line program get sent out before the process is torn down.
> The HTrace C client should support pluggable span receivers
> -----------------------------------------------------------
>
> Key: HTRACE-169
> URL: https://issues.apache.org/jira/browse/HTRACE-169
> Project: HTrace
> Issue Type: New Feature
> Affects Versions: 3.2.0
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
>
> The HTrace C client should support pluggable span receivers in much the same
> way that the Java client supports them.
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