commit f7c0f75275d0fde2d8b7614f1501f0ad0cd3a01c
author Mark Salyzyn <salyzyn@google.com> Tue Mar 03 13:39:37 2015 -0800
committer Mark Salyzyn <salyzyn@google.com> Wed Mar 18 12:43:23 2015 -0700
tree c0470bc2f9663bb790dbce92c10d027954959a8f
parent 5aa097c8a7b9326e1add7a23bf4d31febd25127b

logd: replace internal CLOCK_MONOTONIC use with sequence numbers

- switch to simpler and faster internal sequence number, drops
  a syscall overhead on 32-bit platforms.
- add ability to break-out of flushTo loop with filter return -1
  allowing in reduction in reader overhead.

Change-Id: Ic5cb2b9afa4d9470153971fc9197b07279e2b79d

logd/LogReader.cpp

diff --git a/logd/LogReader.cpp b/logd/LogReader.cpp
index 26df087..f7df275 100644
--- a/logd/LogReader.cpp
+++ b/logd/LogReader.cpp
@@ -100,50 +100,51 @@
         nonBlock = true;
     }
 
-    // Convert realtime to monotonic time
-    if (start == log_time::EPOCH) {
-        start = LogTimeEntry::EPOCH;
-    } else {
+    uint64_t sequence = 1;
+    // Convert realtime to sequence number
+    if (start != log_time::EPOCH) {
         class LogFindStart {
             const pid_t mPid;
             const unsigned mLogMask;
             bool startTimeSet;
             log_time &start;
-            log_time last;
+            uint64_t &sequence;
+            uint64_t last;
 
         public:
-            LogFindStart(unsigned logMask, pid_t pid, log_time &start)
+            LogFindStart(unsigned logMask, pid_t pid, log_time &start, uint64_t &sequence)
                     : mPid(pid)
                     , mLogMask(logMask)
                     , startTimeSet(false)
                     , start(start)
-                    , last(LogTimeEntry::EPOCH)
+                    , sequence(sequence)
+                    , last(sequence)
             { }
 
-            static bool callback(const LogBufferElement *element, void *obj) {
+            static int callback(const LogBufferElement *element, void *obj) {
                 LogFindStart *me = reinterpret_cast<LogFindStart *>(obj);
-                if (!me->startTimeSet
-                        && (!me->mPid || (me->mPid == element->getPid()))
+                if ((!me->mPid || (me->mPid == element->getPid()))
                         && (me->mLogMask & (1 << element->getLogId()))) {
                     if (me->start == element->getRealTime()) {
-                        me->start = element->getMonotonicTime();
+                        me->sequence = element->getSequence();
                         me->startTimeSet = true;
+                        return -1;
                     } else {
                         if (me->start < element->getRealTime()) {
-                            me->start = me->last;
+                            me->sequence = me->last;
                             me->startTimeSet = true;
+                            return -1;
                         }
-                        me->last = element->getMonotonicTime();
+                        me->last = element->getSequence();
                     }
                 }
                 return false;
             }
 
             bool found() { return startTimeSet; }
-        } logFindStart(logMask, pid, start);
+        } logFindStart(logMask, pid, start, sequence);
 
-        logbuf().flushTo(cli, LogTimeEntry::EPOCH,
-                         FlushCommand::hasReadLogs(cli),
+        logbuf().flushTo(cli, sequence, FlushCommand::hasReadLogs(cli),
                          logFindStart.callback, &logFindStart);
 
         if (!logFindStart.found()) {
@@ -151,12 +152,11 @@
                 doSocketDelete(cli);
                 return false;
             }
-            log_time now(CLOCK_MONOTONIC);
-            start = now;
+            sequence = LogBufferElement::getCurrentSequence();
         }
     }
 
-    FlushCommand command(*this, nonBlock, tail, logMask, pid, start);
+    FlushCommand command(*this, nonBlock, tail, logMask, pid, sequence);
     command.runSocketCommand(cli);
     return true;
 }