[lttng-dev] [PATCH lttng-tools] Atomically update relayd stream and session id

[Mathieu Desnoyers]

* David Goulet (dgoulet at efficios.com) wrote:
> Improve protection to the variables where the uatomic_add_return() call
> does a volatile access and returns the value atomically incremented.
> 
> Enclose that in two new functions, one for each id, which helps with the
> code semantic and brings a single call site for the value update making
> the code easier to scale and understand when adding contention to those
> variables.
> 
> Signed-off-by: David Goulet <dgoulet at efficios.com>

This won't build on 32-bit architectures, due to lack of 64-bit atomic
ops.

Thanks,

Mathieu

> ---
>  src/bin/lttng-relayd/lttng-relayd.h |   19 +++++++++++++++++++
>  src/bin/lttng-relayd/main.c         |    9 +++++----
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/src/bin/lttng-relayd/lttng-relayd.h b/src/bin/lttng-relayd/lttng-relayd.h
> index edd32d6..b2566a1 100644
> --- a/src/bin/lttng-relayd/lttng-relayd.h
> +++ b/src/bin/lttng-relayd/lttng-relayd.h
> @@ -23,6 +23,9 @@
>  #include <urcu.h>
>  #include <urcu/wfqueue.h>
>  
> +extern uint64_t relayd_last_stream_id;
> +extern uint64_t relayd_last_session_id;
> +
>  /*
>   * Queue used to enqueue relay requests
>   */
> @@ -81,4 +84,20 @@ struct relay_command {
>  	unsigned int version_check_done:1;
>  };
>  
> +/*
> + * Atomically increment the id and return the next stream id.
> + */
> +static inline uint64_t relayd_get_next_stream_id(void)
> +{
> +	return (uint64_t) uatomic_add_return(&relayd_last_stream_id, 1);
> +}
> +
> +/*
> + * Atomically increment the id and return the next session id.
> + */
> +static inline uint64_t relayd_get_next_session_id(void)
> +{
> +	return (uint64_t) uatomic_add_return(&relayd_last_session_id, 1);
> +}
> +
>  #endif /* LTTNG_RELAYD_H */
> diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
> index 6627310..a042ce6 100644
> --- a/src/bin/lttng-relayd/main.c
> +++ b/src/bin/lttng-relayd/main.c
> @@ -82,8 +82,9 @@ static pthread_t listener_thread;
>  static pthread_t dispatcher_thread;
>  static pthread_t worker_thread;
>  
> -static uint64_t last_relay_stream_id;
> -static uint64_t last_relay_session_id;
> +/* Declared extern in lttng-relayd.h */
> +uint64_t relayd_last_stream_id;
> +uint64_t relayd_last_session_id;
>  
>  /*
>   * Relay command queue.
> @@ -968,7 +969,7 @@ int relay_create_session(struct lttcomm_relayd_hdr *recv_hdr,
>  		goto error;
>  	}
>  
> -	session->id = ++last_relay_session_id;
> +	session->id = relayd_get_next_session_id();
>  	session->sock = cmd->sock;
>  	cmd->session = session;
>  
> @@ -1032,7 +1033,7 @@ int relay_add_stream(struct lttcomm_relayd_hdr *recv_hdr,
>  	}
>  
>  	rcu_read_lock();
> -	stream->stream_handle = ++last_relay_stream_id;
> +	stream->stream_handle = relayd_get_next_stream_id();
>  	stream->prev_seq = -1ULL;
>  	stream->session = session;
>  
> -- 
> 1.7.10.4
> 
> 
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> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

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