Added a bionic systrace class and tracing to pthread_mutex.cpp.

bionic_systrace.h contains an implementation of tracing that
can be used with systrace.py and its associated viewer.  pthread_mutex
now uses this tracing to track pthread_mutex contention, which can be
enabled by using the "bionic" command line option to systrace.

Bug: 15116468
Change-Id: I30ed5b377c91ca4c36568a0e647ddf95d4e4a61a

libc/Android.mk

@@ -94,6 +94,7 @@ libc_bionic_src_files := \
     bionic/access.cpp \
     bionic/assert.cpp \
     bionic/atof.cpp \
+    bionic/bionic_systrace.cpp \
     bionic/bionic_time_conversions.cpp \
     bionic/brk.cpp \
     bionic/c16rtomb.cpp \

libc/bionic/bionic_systrace.cpp

@@ -0,0 +1,107 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+#include <cutils/trace.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "private/bionic_systrace.h"
+#include "private/libc_logging.h"
+
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+
+#define WRITE_OFFSET   32
+
+static const prop_info* g_pinfo = NULL;
+static uint32_t g_serial = -1;
+static uint64_t g_tags = 0;
+static int g_trace_marker_fd = -1;
+
+static bool should_trace() {
+  // If g_pinfo is null, this means that systrace hasn't been run and it's safe to
+  // assume that no trace writing will need to take place.  However, to avoid running
+  // this costly find check each time, we set it to a non-tracing value so that next
+  // time, it will just check the serial to see if the value has been changed.
+  // this function also deals with the bootup case, during which the call to property
+  // set will fail if the property server hasn't yet started.
+  if (g_pinfo == NULL) {
+    g_pinfo = __system_property_find("debug.atrace.tags.enableflags");
+    if (g_pinfo == NULL) {
+      __system_property_set("debug.atrace.tags.enableflags", "0");
+      g_pinfo = __system_property_find("debug.atrace.tags.enableflags");
+      if (g_pinfo == NULL) {
+        return false;
+      }
+    }
+  }
+
+  // Find out which tags have been enabled on the command line and set
+  // the value of tags accordingly.  If the value of the property changes,
+  // the serial will also change, so the costly system_property_read function
+  // can be avoided by calling the much cheaper system_property_serial
+  // first.  The values within pinfo may change, but its location is guaranteed
+  // not to move.
+  const uint32_t cur_serial = __system_property_serial(g_pinfo);
+  if (cur_serial != g_serial) {
+    g_serial = cur_serial;
+    char value[PROP_VALUE_MAX];
+    __system_property_read(g_pinfo, 0, value);
+    g_tags = strtoull(value, NULL, 0);
+  }
+
+  // Finally, verify that this tag value enables bionic tracing.
+  return ((g_tags & ATRACE_TAG_BIONIC) != 0);
+}
+
+ScopedTrace::ScopedTrace(const char* message) {
+  if (!should_trace()) {
+    return;
+  }
+
+  if (g_trace_marker_fd == -1) {
+    g_trace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_WRONLY | O_CLOEXEC);
+    if (g_trace_marker_fd == -1) {
+      __libc_fatal("Could not open kernel trace file: %s\n", strerror(errno));
+    }
+  }
+
+  // If bionic tracing has been enabled, then write the message to the
+  // kernel trace_marker.
+  int length = strlen(message);
+  char buf[length + WRITE_OFFSET];
+  size_t len = snprintf(buf, length + WRITE_OFFSET, "B|%d|%s", getpid(), message);
+  ssize_t wbytes = TEMP_FAILURE_RETRY(write(g_trace_marker_fd, buf, len));
+
+  // Error while writing
+  if (static_cast<size_t>(wbytes) != len) {
+    __libc_fatal("Could not write to kernel trace file: %s\n", strerror(errno));
+  }
+}
+
+ScopedTrace::~ScopedTrace() {
+  if (!should_trace()) {
+    return;
+  }
+
+  ssize_t wbytes = TEMP_FAILURE_RETRY(write(g_trace_marker_fd, "E", 1));
+
+  // Error while writing
+  if (static_cast<size_t>(wbytes) != 1) {
+    __libc_fatal("Could not write to kernel trace file: %s\n", strerror(errno));
+  }
+}

libc/bionic/pthread_mutex.cpp

@@ -39,6 +39,8 @@
 #include "private/bionic_futex.h"
 #include "private/bionic_tls.h"
 
+#include "private/bionic_systrace.h"
+
 extern void pthread_debug_mutex_lock_check(pthread_mutex_t *mutex);
 extern void pthread_debug_mutex_unlock_check(pthread_mutex_t *mutex);
 
@@ -333,6 +335,10 @@ static inline void _normal_lock(pthread_mutex_t* mutex, int shared) {
          * that the mutex is in state 2 when we go to sleep on it, which
          * guarantees a wake-up call.
          */
+
+         ScopedTrace trace("Contending for pthread mutex");
+
+
         while (__bionic_swap(locked_contended, &mutex->value) != unlocked) {
             __futex_wait_ex(&mutex->value, shared, locked_contended, NULL);
         }
@@ -473,6 +479,8 @@ int pthread_mutex_lock(pthread_mutex_t* mutex) {
         mvalue = mutex->value;
     }
 
+    ScopedTrace trace("Contending for pthread mutex");
+
     for (;;) {
         int newval;
 
@@ -626,6 +634,8 @@ static int __pthread_mutex_timedlock(pthread_mutex_t* mutex, const timespec* abs
       return 0;
     }
 
+    ScopedTrace trace("Contending for timed pthread mutex");
+
     // Loop while needed.
     while (__bionic_swap(locked_contended, &mutex->value) != unlocked) {
       if (__timespec_from_absolute(&ts, abs_timeout, clock) < 0) {
@@ -658,6 +668,8 @@ static int __pthread_mutex_timedlock(pthread_mutex_t* mutex, const timespec* abs
     mvalue = mutex->value;
   }
 
+  ScopedTrace trace("Contending for timed pthread mutex");
+
   while (true) {
     // If the value is 'unlocked', try to acquire it directly.
     // NOTE: put state to 2 since we know there is contention.

libc/private/bionic_systrace.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2014 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 BIONIC_SYSTRACE_H
+#define BIONIC_SYSTRACE_H
+
+#include "bionic_macros.h"
+
+// Tracing class for bionic. To begin a trace at a specified point:
+//   ScopedTrace("Trace message");
+// The trace will end when the contructor goes out of scope.
+
+class ScopedTrace {
+ public:
+  explicit ScopedTrace(const char* message);
+  ~ScopedTrace();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedTrace);
+};
+
+#endif