[lttng-dev] [PATCH lttng-ust] Remove mention of locking issues associated with dlopen usage

[Mathieu Desnoyers]

* Jérémie Galarneau (jeremie.galarneau at efficios.com) wrote:
> This notice has been removed from the README as part of revision b834dead.
> 
> Add a warning relating to dlclose() usage detailed in issue 447 in both the
> man page and the README file.

merged into master and stable-2.1, thanks!

Mathieu

> 
> Signed-off-by: Jérémie Galarneau <jeremie.galarneau at efficios.com>
> ---
>  README              |  6 +++++-
>  doc/man/lttng-ust.3 | 14 +++++++-------
>  2 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/README b/README
> index 55c72df..390a719 100644
> --- a/README
> +++ b/README
> @@ -75,7 +75,7 @@ USAGE:
>      - Include the tracepoint provider header into all C files using
>        the provider.
>      - Example:
> -        tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example.*
> +      - tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example.*
>  
>    2) Compile the Tracepoint Provider separately from the application,
>       using dynamic linking:
> @@ -97,6 +97,10 @@ USAGE:
>  
>    - Enable instrumentation and control tracing with the "lttng" command
>      from lttng-tools. See lttng-tools doc/quickstart.txt.
> +  - Note about dlclose() usage: it is not safe to use dlclose on a
> +    provider shared object that is being actively used for tracing due
> +    to a lack of reference counting from lttng-ust to the used shared
> +    object.
>  
>  ENVIRONMENT VARIABLES:
>  
> diff --git a/doc/man/lttng-ust.3 b/doc/man/lttng-ust.3
> index 08927c6..7cc3bfd 100644
> --- a/doc/man/lttng-ust.3
> +++ b/doc/man/lttng-ust.3
> @@ -265,7 +265,7 @@ carefully:
>      - Include the tracepoint provider header into all C files using
>        the provider.
>      - Example:
> -        tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example
> +      - tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example
>  
>    2) Compile the Tracepoint Provider separately from the application,
>       using dynamic linking:
> @@ -280,15 +280,15 @@ carefully:
>      - Link application with "\-ldl".
>      - Set a LD_PRELOAD environment to preload the tracepoint provider
>        shared object before starting the application when tracing is
> -      needed.
> +      needed. Another way is to dlopen the tracepoint probe when needed
> +      by the application.
>      - Example:
>        - tests/demo/   demo.c  tp*.c ust_tests_demo*.h demo-trace
>  
> -  - Note about dlopen() usage: due to locking side-effects due to the
> -    way libc lazily resolves Thread-Local Storage (TLS) symbols when a
> -    library is dlopen'd, linking the tracepoint probe or liblttng-ust
> -    with dlopen() is discouraged. They should be linked with the
> -    application using "\-llibname" or loaded with LD_PRELOAD.
> +  - Note about dlclose() usage: it is not safe to use dlclose on a
> +    provider shared object that is being actively used for tracing due
> +    to a lack of reference counting from lttng-ust to the used shared
> +    object.
>    - Enable instrumentation and control tracing with the "lttng" command
>      from lttng-tools. See lttng-tools doc/quickstart.txt.
>    - Note for C++ support: although an application instrumented with
> -- 
> 1.8.1.5
> 
> 
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com