[POC][PATCH v4] tools/lib/traceevent: make libtraceevent thread safe

[Tzvetomir Stoyanov <tstoyanov@vmware.com>]

This patch is a PoC about transforming libtraceevent
into a thread safe library. It implements per thread local
storage and internal APIs to access it. It covers only
tep->last_event cache, but easily can be extended with all
library's thread sensitive data.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
---
v2: Added local thread data per tep context
v3: Implemented APIs to access specific tread local data,
    instead of the whole struct tep_thread_data.
v4: Simplify the implementation to keep cache only for the last
    used tep context in current thread, instead to track
    cache for all tep contexts. Remove "tep_" prefix of functions,
    as these are internal APIs and are not going to be exposed to
    the library users.
---
 tools/lib/traceevent/event-parse-local.h  | 16 ++++--
 tools/lib/traceevent/event-parse-thread.c | 62 +++++++++++++++++++++++
 tools/lib/traceevent/event-parse.c        | 21 ++++----
 3 files changed, 87 insertions(+), 12 deletions(-)
 create mode 100644 tools/lib/traceevent/event-parse-thread.c

diff --git a/tools/lib/traceevent/event-parse-local.h b/tools/lib/traceevent/event-parse-local.h
index 9a092dd4a86d..bf3f810ce02f 100644
--- a/tools/lib/traceevent/event-parse-local.h
+++ b/tools/lib/traceevent/event-parse-local.h
@@ -14,6 +14,13 @@ struct func_list;
 struct event_handler;
 struct func_resolver;
 
+/* cache */
+struct tep_thread_data {
+	struct tep_handle *tep;
+
+	struct tep_event *last_event;
+};
+
 struct tep_handle {
 	int ref_count;
 
@@ -83,9 +90,6 @@ struct tep_handle {
 	struct event_handler *handlers;
 	struct tep_function_handler *func_handlers;
 
-	/* cache */
-	struct tep_event *last_event;
-
 	char *trace_clock;
 };
 
@@ -96,4 +100,10 @@ unsigned short tep_data2host2(struct tep_handle *pevent, unsigned short data);
 unsigned int tep_data2host4(struct tep_handle *pevent, unsigned int data);
 unsigned long long tep_data2host8(struct tep_handle *pevent, unsigned long long data);
 
+/* tep cache per thread */
+struct tep_event *get_thread_local_event_by_id(struct tep_handle *tep, int id);
+struct tep_event *
+get_thread_local_event_by_name(struct tep_handle *tep, const char *name, const char *sys);
+void set_thread_local_event_cache(struct tep_handle *tep, struct tep_event *event);
+
 #endif /* _PARSE_EVENTS_INT_H */
diff --git a/tools/lib/traceevent/event-parse-thread.c b/tools/lib/traceevent/event-parse-thread.c
new file mode 100644
index 000000000000..b575f7d8424e
--- /dev/null
+++ b/tools/lib/traceevent/event-parse-thread.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: LGPL-2.1
+/*
+ * Copyright (C) 2009, 2010 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
+ *
+ */
+
+#include "event-parse.h"
+#include "event-parse-local.h"
+#include "event-utils.h"
+
+static __thread struct tep_thread_data tep_thread_local;
+
+/**
+ * get_thread_local_event_by_id - Find event with given id in the cache
+ * @tep: a handle to the tep context
+ * @id: event's id
+ *
+ * Searches in the cache for event with given id
+ */
+struct tep_event *get_thread_local_event_by_id(struct tep_handle *tep, int id)
+{
+
+	if (tep_thread_local->last_event && tep_thread_local->tep == tep &&
+	    tep_thread_local->last_event->id == id)
+		return tep_thread_local->last_event;
+
+	return NULL;
+}
+
+/**
+ * get_thread_local_event_by_name - Find event with given name and sys in the cache
+ * @tep: a handle to the tep context
+ * @name: event's name
+ * @sys: event's system
+ *
+ * Searches in the cache for event with given name and system
+ */
+struct tep_event *
+get_thread_local_event_by_name(struct tep_handle *tep, const char *name, const char *sys)
+{
+	if (tep_thread_local->last_event &&
+	    tep_thread_local->tep == tep &&
+	    strcmp(tep_thread_local->last_event->name, name) == 0 &&
+	    (!sys || strcmp(tep_thread_local->last_event->system, sys) == 0))
+		return tep_thread_local->last_event;
+
+	return NULL;
+}
+
+/**
+ * set_thread_local_event_cache - set last used event in the cache
+ * @tep: a handle to the tep context
+ * @event: pointer to the last used event
+ *
+ * Sets last used event in the cache, to speed up the next searches
+ */
+void set_thread_local_event_cache(struct tep_handle *tep, struct tep_event *event)
+{
+	tep_thread_local->last_event = event;
+}
+
+
diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index a5048c1b9bec..ea6292c61ad4 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -3485,10 +3485,11 @@ struct tep_event *tep_find_event(struct tep_handle *pevent, int id)
 	struct tep_event **eventptr;
 	struct tep_event key;
 	struct tep_event *pkey = &key;
+	struct tep_event *event_cache = get_thread_local_event_by_id(pevent, id);
 
 	/* Check cache first */
-	if (pevent->last_event && pevent->last_event->id == id)
-		return pevent->last_event;
+	if (event_cache)
+		return event_cache;
 
 	key.id = id;
 
@@ -3496,7 +3497,7 @@ struct tep_event *tep_find_event(struct tep_handle *pevent, int id)
 			   sizeof(*pevent->events), events_id_cmp);
 
 	if (eventptr) {
-		pevent->last_event = *eventptr;
+		set_thread_local_event_cache(pevent, *eventptr);
 		return *eventptr;
 	}
 
@@ -3516,13 +3517,13 @@ struct tep_event *
 tep_find_event_by_name(struct tep_handle *pevent,
 		       const char *sys, const char *name)
 {
-	struct tep_event *event = NULL;
 	int i;
+	struct tep_event *event = NULL;
+	struct tep_event *event_cache = get_thread_local_event_by_name(pevent, name, sys);
 
-	if (pevent->last_event &&
-	    strcmp(pevent->last_event->name, name) == 0 &&
-	    (!sys || strcmp(pevent->last_event->system, sys) == 0))
-		return pevent->last_event;
+	/* Check cache first */
+	if (event_cache)
+		return event_cache;
 
 	for (i = 0; i < pevent->nr_events; i++) {
 		event = pevent->events[i];
@@ -3533,10 +3534,12 @@ tep_find_event_by_name(struct tep_handle *pevent,
 				break;
 		}
 	}
+
 	if (i == pevent->nr_events)
 		event = NULL;
+	if (event)
+		set_thread_local_event_cache(pevent, event);
 
-	pevent->last_event = event;
 	return event;
 }
 
-- 
2.19.1