[FFmpeg-devel] [PATCH 1/2] avutil/log: Add av_log_once() for printing a message just once per instance

[Michael Niedermayer]

Compared to ad-hoc if(printed) ... code this allows the user to disable
it with a flag and see all repeated messages, it is also simpler

TODO: APIChanges & version bump

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavutil/log.c | 15 +++++++++++++++
 libavutil/log.h | 19 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/libavutil/log.c b/libavutil/log.c
index e8a0db7716..7646e18cfa 100644
--- a/libavutil/log.c
+++ b/libavutil/log.c
@@ -372,6 +372,21 @@ void av_log(void* avcl, int level, const char *fmt, ...)
     va_end(vl);
 }
 
+void av_log_once(void* avcl, int level, int *state, const char *fmt, ...)
+{
+    if (!((flags & AV_LOG_SKIP_REPEATED) && *state)) {
+        AVClass* avc = avcl ? *(AVClass **) avcl : NULL;
+        va_list vl;
+        va_start(vl, fmt);
+        if (avc && avc->version >= (50 << 16 | 15 << 8 | 2) &&
+            avc->log_level_offset_offset && level >= AV_LOG_FATAL)
+            level += *(int *) (((uint8_t *) avcl) + avc->log_level_offset_offset);
+        av_vlog(avcl, level, fmt, vl);
+        va_end(vl);
+        *state = 1;
+    }
+}
+
 void av_vlog(void* avcl, int level, const char *fmt, va_list vl)
 {
     void (*log_callback)(void*, int, const char*, va_list) = av_log_callback;
diff --git a/libavutil/log.h b/libavutil/log.h
index d9554e609d..618d0d1817 100644
--- a/libavutil/log.h
+++ b/libavutil/log.h
@@ -233,6 +233,25 @@ typedef struct AVClass {
  */
 void av_log(void *avcl, int level, const char *fmt, ...) av_printf_format(3, 4);
 
+/**
+ * Send the specified message to the log once if the level is less than or equal
+ * to the current av_log_level. By default, all logging messages are sent to
+ * stderr. This behavior can be altered by setting a different logging callback
+ * function.
+ * If AV_LOG_SKIP_REPEATED is set each message (each unique state) will only be
+ * printed once. If its not set then this behaves live av_log()
+ * @see av_log
+ *
+ * @param avcl A pointer to an arbitrary struct of which the first field is a
+ *        pointer to an AVClass struct or NULL if general log.
+ * @param level The importance level of the message expressed using a @ref
+ *        lavu_log_constants "Logging Constant".
+ * @param fmt The format string (printf-compatible) that specifies how
+ *        subsequent arguments are converted to output.
+ * @param state a variable to keep trak of if a message has already been printed
+ *        this must be initialized to 0 before the first use.
+ */
+void av_log_once(void *avcl, int level, int *state, const char *fmt, ...) av_printf_format(4, 5);
 
 /**
  * Send the specified message to the log if the level is less than or equal
-- 
2.24.0