From 54bfab9cb07e72157aa5295902263f4b2e37ed0b Mon Sep 17 00:00:00 2001
From: Jed Davis <jld@mozilla.com>
Date: Thu, 11 Jul 2013 23:41:19 -0400
Subject: [PATCH] Bug 892201: replace SPS signal handler completion busy loop
 with POSIX semaphore. r=benwa

--HG--
extra : rebase_source : 48bfcc1a352ae600dd1294d5b5e122ad0c58a745
---
 tools/profiler/platform-linux.cc | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/tools/profiler/platform-linux.cc b/tools/profiler/platform-linux.cc
index ef0f68b1bb9..abafadc5f18 100644
--- a/tools/profiler/platform-linux.cc
+++ b/tools/profiler/platform-linux.cc
@@ -53,6 +53,7 @@
 #include <sys/stat.h>   // open
 #include <fcntl.h>      // open
 #include <unistd.h>     // sysconf
+#include <semaphore.h>
 #ifdef __GLIBC__
 #include <execinfo.h>   // backtrace, backtrace_symbols
 #endif  // def __GLIBC__
@@ -62,6 +63,7 @@
 #include "platform.h"
 #include "GeckoProfilerImpl.h"
 #include "mozilla/Mutex.h"
+#include "mozilla/Atomics.h"
 #include "ProfileEntry.h"
 #include "nsThreadUtils.h"
 #include "TableTicker.h"
@@ -140,7 +142,8 @@ struct SamplerRegistry {
 
 Sampler *SamplerRegistry::sampler = NULL;
 
-static ThreadProfile* sCurrentThreadProfile = NULL;
+static mozilla::Atomic<ThreadProfile*> sCurrentThreadProfile;
+static sem_t sSignalHandlingDone;
 
 static void ProfilerSaveSignalHandler(int signal, siginfo_t* info, void* context) {
   Sampler::GetActiveSampler()->RequestSave();
@@ -204,6 +207,7 @@ static void ProfilerSignalHandler(int signal, siginfo_t* info, void* context) {
   Sampler::GetActiveSampler()->Tick(sample);
 
   sCurrentThreadProfile = NULL;
+  sem_post(&sSignalHandlingDone);
 }
 
 int tgkill(pid_t tgid, pid_t tid, int signalno) {
@@ -270,8 +274,7 @@ static void* SignalSender(void* arg) {
         }
 
         // Wait for the signal handler to run before moving on to the next one
-        while (sCurrentThreadProfile)
-          sched_yield();
+        sem_wait(&sSignalHandlingDone);
       }
     }
 
@@ -304,6 +307,13 @@ void Sampler::Start() {
 
   SamplerRegistry::AddActiveSampler(this);
 
+  // Initialize signal handler communication
+  sCurrentThreadProfile = NULL;
+  if (sem_init(&sSignalHandlingDone, /* pshared: */ 0, /* value: */ 0) != 0) {
+    LOG("Error initializing semaphore");
+    return;
+  }
+
   // Request profiling signals.
   LOG("Request signal");
   struct sigaction sa;