[PATCH v2 2/9] trace2: convert tr2tls_thread_ctx.thread_name from strbuf to flex array

["Jeff Hostetler via GitGitGadget" <gitgitgadget@gmail.com>]

From: Jeff Hostetler <jeffhost@microsoft.com>

Move the thread name to a flex array at the bottom of the Trace2
thread local storage data and get rid of the strbuf.

Let the flex array have the full computed value of the thread name
without truncation.

Change the PERF target to truncate the thread name so that the columns
still line up.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 trace2/tr2_tgt_event.c |  2 +-
 trace2/tr2_tgt_perf.c  |  7 ++++---
 trace2/tr2_tls.c       | 25 +++++++++++++------------
 trace2/tr2_tls.h       | 10 +---------
 4 files changed, 19 insertions(+), 25 deletions(-)

diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
index 3a0014417cc..ca48d00aebc 100644
--- a/trace2/tr2_tgt_event.c
+++ b/trace2/tr2_tgt_event.c
@@ -88,7 +88,7 @@ static void event_fmt_prepare(const char *event_name, const char *file,
 
 	jw_object_string(jw, "event", event_name);
 	jw_object_string(jw, "sid", tr2_sid_get());
-	jw_object_string(jw, "thread", ctx->thread_name.buf);
+	jw_object_string(jw, "thread", ctx->thread_name);
 
 	/*
 	 * In brief mode, only emit <time> on these 2 event types.
diff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c
index e4acca13d64..fd6cce3efe5 100644
--- a/trace2/tr2_tgt_perf.c
+++ b/trace2/tr2_tgt_perf.c
@@ -23,6 +23,7 @@ static int tr2env_perf_be_brief;
 
 #define TR2FMT_PERF_FL_WIDTH (28)
 #define TR2FMT_PERF_MAX_EVENT_NAME (12)
+#define TR2FMT_PERF_MAX_THREAD_NAME (24)
 #define TR2FMT_PERF_REPO_WIDTH (3)
 #define TR2FMT_PERF_CATEGORY_WIDTH (12)
 
@@ -105,9 +106,9 @@ static void perf_fmt_prepare(const char *event_name,
 	}
 
 	strbuf_addf(buf, "d%d | ", tr2_sid_depth());
-	strbuf_addf(buf, "%-*s | %-*s | ", TR2_MAX_THREAD_NAME,
-		    ctx->thread_name.buf, TR2FMT_PERF_MAX_EVENT_NAME,
-		    event_name);
+	strbuf_addf(buf, "%-*.*s | %-*s | ", TR2FMT_PERF_MAX_THREAD_NAME,
+		    TR2FMT_PERF_MAX_THREAD_NAME, ctx->thread_name,
+		    TR2FMT_PERF_MAX_EVENT_NAME, event_name);
 
 	len = buf->len + TR2FMT_PERF_REPO_WIDTH;
 	if (repo)
diff --git a/trace2/tr2_tls.c b/trace2/tr2_tls.c
index 7da94aba522..ed99a234b95 100644
--- a/trace2/tr2_tls.c
+++ b/trace2/tr2_tls.c
@@ -34,7 +34,18 @@ void tr2tls_start_process_clock(void)
 struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,
 					     uint64_t us_thread_start)
 {
-	struct tr2tls_thread_ctx *ctx = xcalloc(1, sizeof(*ctx));
+	struct tr2tls_thread_ctx *ctx;
+	struct strbuf buf_name = STRBUF_INIT;
+	int thread_id = tr2tls_locked_increment(&tr2_next_thread_id);
+
+	if (thread_id)
+		strbuf_addf(&buf_name, "th%02d:", thread_id);
+	strbuf_addstr(&buf_name, thread_name);
+
+	FLEX_ALLOC_MEM(ctx, thread_name, buf_name.buf, buf_name.len);
+	strbuf_release(&buf_name);
+
+	ctx->thread_id = thread_id;
 
 	/*
 	 * Implicitly "tr2tls_push_self()" to capture the thread's start
@@ -45,15 +56,6 @@ struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,
 	ctx->array_us_start = (uint64_t *)xcalloc(ctx->alloc, sizeof(uint64_t));
 	ctx->array_us_start[ctx->nr_open_regions++] = us_thread_start;
 
-	ctx->thread_id = tr2tls_locked_increment(&tr2_next_thread_id);
-
-	strbuf_init(&ctx->thread_name, 0);
-	if (ctx->thread_id)
-		strbuf_addf(&ctx->thread_name, "th%02d:", ctx->thread_id);
-	strbuf_addstr(&ctx->thread_name, thread_name);
-	if (ctx->thread_name.len > TR2_MAX_THREAD_NAME)
-		strbuf_setlen(&ctx->thread_name, TR2_MAX_THREAD_NAME);
-
 	pthread_setspecific(tr2tls_key, ctx);
 
 	return ctx;
@@ -95,7 +97,6 @@ void tr2tls_unset_self(void)
 
 	pthread_setspecific(tr2tls_key, NULL);
 
-	strbuf_release(&ctx->thread_name);
 	free(ctx->array_us_start);
 	free(ctx);
 }
@@ -113,7 +114,7 @@ void tr2tls_pop_self(void)
 	struct tr2tls_thread_ctx *ctx = tr2tls_get_self();
 
 	if (!ctx->nr_open_regions)
-		BUG("no open regions in thread '%s'", ctx->thread_name.buf);
+		BUG("no open regions in thread '%s'", ctx->thread_name);
 
 	ctx->nr_open_regions--;
 }
diff --git a/trace2/tr2_tls.h b/trace2/tr2_tls.h
index a90bd639d48..64d97c5ac03 100644
--- a/trace2/tr2_tls.h
+++ b/trace2/tr2_tls.h
@@ -3,17 +3,12 @@
 
 #include "strbuf.h"
 
-/*
- * Arbitry limit for thread names for column alignment.
- */
-#define TR2_MAX_THREAD_NAME (24)
-
 struct tr2tls_thread_ctx {
-	struct strbuf thread_name;
 	uint64_t *array_us_start;
 	size_t alloc;
 	size_t nr_open_regions; /* plays role of "nr" in ALLOC_GROW */
 	int thread_id;
+	char thread_name[FLEX_ARRAY];
 };
 
 /*
@@ -25,9 +20,6 @@ struct tr2tls_thread_ctx {
  * non-zero thread-ids to help distinguish messages from concurrent
  * threads.
  *
- * Truncate the thread name if necessary to help with column alignment
- * in printf-style messages.
- *
  * In this and all following functions the term "self" refers to the
  * current thread.
  */
-- 
gitgitgadget