base: add GetNumberOfThreads() to Linux and Android.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/12193017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@180914 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 30 insertions, 0 deletions

diff --git a/base/process_util.h b/base/process_util.h
index fe21adf..10d3028 100644
--- a/base/process_util.h
+++ b/base/process_util.h
@@ -197,6 +197,12 @@ BASE_EXPORT FilePath GetProcessExecutablePath(ProcessHandle process);
 // Exposed for testing.
 BASE_EXPORT int ParseProcStatCPU(const std::string& input);
 
+// Get the number of threads of |process| as available in /proc/<pid>/stat.
+// This should be used with care as no synchronization with running threads is
+// done. This is mostly useful to guarantee being single-threaded.
+// Returns 0 on failure.
+BASE_EXPORT int GetNumberOfThreads(ProcessHandle process);
+
 // The maximum allowed value for the OOM score.
 const int kMaxOomScore = 1000;
 
diff --git a/base/process_util_linux.cc b/base/process_util_linux.cc
index 06077a8..36f377b 100644
--- a/base/process_util_linux.cc
+++ b/base/process_util_linux.cc
@@ -46,6 +46,7 @@ enum ProcStatsFields {
   VM_PGRP           = 4,   // Process group id.
   VM_UTIME          = 13,  // Time scheduled in user mode in clock ticks.
   VM_STIME          = 14,  // Time scheduled in kernel mode in clock ticks.
+  VM_NUMTHREADS     = 19,  // Number of threads.
   VM_VSIZE          = 22,  // Virtual memory size in bytes.
   VM_RSS            = 23,  // Resident Set Size in pages.
 };
@@ -594,6 +595,10 @@ int ParseProcStatCPU(const std::string& input) {
   return utime + stime;
 }
 
+int GetNumberOfThreads(ProcessHandle process) {
+  return ReadProcStatsAndGetFieldAsInt(process, VM_NUMTHREADS);
+}
+
 namespace {
 
 // The format of /proc/meminfo is:
diff --git a/base/process_util_unittest.cc b/base/process_util_unittest.cc
index 9897e41..309b87c 100644
--- a/base/process_util_unittest.cc
+++ b/base/process_util_unittest.cc
@@ -19,6 +19,7 @@
 #include "base/test/test_timeouts.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/platform_thread.h"
+#include "base/threading/thread.h"
 #include "base/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/multiprocess_func_list.h"
@@ -944,6 +945,24 @@ TEST_F(ProcessUtilTest, ParseProcStatCPU) {
 
   EXPECT_EQ(0, base::ParseProcStatCPU(kSelfStat));
 }
+
+TEST_F(ProcessUtilTest, GetNumberOfThreads) {
+  const base::ProcessHandle current = base::GetCurrentProcessHandle();
+  const int initial_threads = base::GetNumberOfThreads(current);
+  ASSERT_GT(initial_threads, 0);
+  const int kNumAdditionalThreads = 10;
+  {
+    scoped_ptr<base::Thread> my_threads[kNumAdditionalThreads];
+    for (int i = 0; i < kNumAdditionalThreads; ++i) {
+      my_threads[i].reset(new base::Thread("GetNumberOfThreadsTest"));
+      my_threads[i]->Start();
+      ASSERT_EQ(base::GetNumberOfThreads(current), initial_threads + 1 + i);
+    }
+  }
+  // The Thread destructor will stop them.
+  ASSERT_EQ(initial_threads, base::GetNumberOfThreads(current));
+}
+
 #endif  // defined(OS_LINUX) || defined(OS_ANDROID)
 
 // TODO(port): port those unit tests.