libutils: add a system-wide tracing utility
This change adds some utility functionality for doing userland tracing
into the kernel trace log.
Change-Id: Id0a8cee9ea515b1d8765afd1cecf472a88b4b9e8
diff --git a/include/utils/Trace.h b/include/utils/Trace.h
new file mode 100644
index 0000000..f33ddf6
--- /dev/null
+++ b/include/utils/Trace.h
@@ -0,0 +1,166 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_TRACE_H
+#define ANDROID_TRACE_H
+
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <cutils/compiler.h>
+#include <utils/threads.h>
+
+// The ATRACE_TAG macro can be defined before including this header to trace
+// using one of the tags defined below. It must be defined to one of the
+// following ATRACE_TAG_* macros. The trace tag is used to filter tracing in
+// userland to avoid some of the runtime cost of tracing when it is not desired.
+//
+// Defining ATRACE_TAG to be ATRACE_TAG_ALWAYS will result in the tracing always
+// being enabled - this should ONLY be done for debug code, as userland tracing
+// has a performance cost even when the trace is not being recorded. Defining
+// ATRACE_TAG to be ATRACE_TAG_NEVER or leaving ATRACE_TAG undefined will result
+// in the tracing always being disabled.
+#define ATRACE_TAG_NEVER 0 // The "never" tag is never enabled.
+#define ATRACE_TAG_ALWAYS (1<<0) // The "always" tag is always enabled.
+#define ATRACE_TAG_GRAPHICS (1<<1)
+#define ATRACE_TAG_LAST (1<<1)
+
+#define ATRACE_TAG_INVALID (~((ATRACE_TAG_LAST - 1) | ATRACE_TAG_LAST))
+
+#ifndef ATRACE_TAG
+#define ATRACE_TAG ATRACE_TAG_NEVER
+#elif ATRACE_TAG > ATRACE_TAG_LAST
+#error ATRACE_TAG must be defined to be one of the tags defined in utils/Trace.h
+#endif
+
+// ATRACE_CALL traces the beginning and end of the current function. To trace
+// the correct start and end times this macro should be the first line of the
+// function body.
+#define ATRACE_CALL() android::ScopedTrace ___tracer(ATRACE_TAG, __FUNCTION__)
+
+// ATRACE_INT traces a named integer value. This can be used to track how the
+// value changes over time in a trace.
+#define ATRACE_INT(name, value) android::Tracer::traceCounter(ATRACE_TAG, name, value)
+
+namespace android {
+
+class Tracer {
+
+public:
+
+ static inline void traceCounter(uint64_t tag, const char* name,
+ int32_t value) {
+ if (!android_atomic_acquire_load(&sIsReady)) {
+ init();
+ }
+ int traceFD = sTraceFD;
+ if (CC_UNLIKELY(tagEnabled(tag) && traceFD != -1)) {
+ char buf[1024];
+ snprintf(buf, 1024, "C|%d|%s|%d", getpid(), name, value);
+ write(traceFD, buf, strlen(buf));
+ }
+ }
+
+ static inline void traceBegin(uint64_t tag, const char* name) {
+ if (CC_UNLIKELY(!android_atomic_acquire_load(&sIsReady))) {
+ init();
+ }
+ int traceFD = sTraceFD;
+ if (CC_UNLIKELY(tagEnabled(tag) && (traceFD != -1))) {
+ char buf[1024];
+ size_t len = snprintf(buf, 1024, "B|%d|%s", getpid(), name);
+ write(traceFD, buf, len);
+ }
+ }
+
+ static inline void traceEnd(uint64_t tag) {
+ if (CC_UNLIKELY(!android_atomic_acquire_load(&sIsReady))) {
+ init();
+ }
+ int traceFD = sTraceFD;
+ if (CC_UNLIKELY(tagEnabled(tag) && (traceFD != -1))) {
+ char buf = 'E';
+ write(traceFD, &buf, 1);
+ }
+ }
+
+private:
+
+ static inline bool tagEnabled(uint64_t tag) {
+ return !(tag & ATRACE_TAG_INVALID) && (tag & sEnabledTags);
+ }
+
+ // init opens the trace marker file for writing and reads the
+ // atrace.tags.enableflags system property. It does this only the first
+ // time it is run, using sMutex for synchronization.
+ static void init();
+
+ // sIsReady is a boolean value indicating whether a call to init() has
+ // completed in this process. It is initialized to 0 and set to 1 when the
+ // first init() call completes. It is set to 1 even if a failure occurred
+ // in init (e.g. the trace marker file couldn't be opened).
+ //
+ // This should be checked by all tracing functions using an atomic acquire
+ // load operation before calling init(). This check avoids the need to lock
+ // a mutex each time a trace function gets called.
+ static volatile int32_t sIsReady;
+
+ // sTraceFD is the file descriptor used to write to the kernel's trace
+ // buffer. It is initialized to -1 and set to an open file descriptor in
+ // init() while a lock on sMutex is held.
+ //
+ // This should only be used by a trace function after init() has
+ // successfully completed.
+ static int sTraceFD;
+
+ // sEnabledTags is the set of tag bits for which tracing is currently
+ // enabled. It is initialized to 0 and set based on the
+ // atrace.tags.enableflags system property in init() while a lock on sMutex
+ // is held.
+ //
+ // This should only be used by a trace function after init() has
+ // successfully completed.
+ static uint64_t sEnabledTags;
+
+ // sMutex is used to protect the execution of init().
+ static Mutex sMutex;
+};
+
+class ScopedTrace {
+
+public:
+ inline ScopedTrace(uint64_t tag, const char* name) :
+ mTag(tag) {
+ Tracer::traceBegin(mTag, name);
+ }
+
+ inline ~ScopedTrace() {
+ Tracer::traceEnd(mTag);
+ }
+
+private:
+
+ uint64_t mTag;
+};
+
+}; // namespace android
+
+#endif // ANDROID_TRACE_H