Reland (2) of Enable allocator shim for Android (crrev.com/1875043003)

tools/cygprofile/cygprofile.cc

Index: tools/cygprofile/cygprofile.cc
diff --git a/tools/cygprofile/cygprofile.cc b/tools/cygprofile/cygprofile.cc
index d699c3e355bd255250df242b449a4a9424bc8b67..368a633c95d4ef6f9ac6b7c3503f837579c8c715 100644
--- a/tools/cygprofile/cygprofile.cc
+++ b/tools/cygprofile/cygprofile.cc
@@ -51,7 +51,25 @@ const char kLogFilenameFormat[] = "%scyglog.%d.%d-%d";
 ThreadLog* const kMagicBeingConstructed = reinterpret_cast<ThreadLog*>(1);
 
 // Per-thread pointer to the current log object.
-static __thread ThreadLog* g_tls_log = NULL;
+pthread_key_t g_tls_slot;
+
+// Used to initialize the tls slot, once per the entire process.
+pthread_once_t g_tls_slot_initializer_once = PTHREAD_ONCE_INIT;
+
+// This variable is to prevent re-entrancy in the __cyg_profile_func_enter()
+// while the TLS slot itself is being initialized. Volatile here is required
+// to avoid compiler otpimizations, as this need to be read in re-entrant code.
+// This variable is NOT accessed from multiple threads (pthread_once guarantees

[pasko, 2016/04/15 11:42:14]

as per offline discussion, this comment needs to be updated to explain the once
write multiple reads.

[Primiano Tucci (use gerrit), 2016/04/15 12:51:07]

Done.

+// that).
+volatile bool g_tls_slot_being_initialized = false;
+
+// Initializes the global TLS slot. This is invoked only once per process.
+static void TLSSlotInitializer()
+{
+    g_tls_slot_being_initialized = true;
+    (void) pthread_key_create(&g_tls_slot, NULL);

[pasko, 2016/04/15 11:42:14]

Everywhere in this file please check return value for:
pthread_key_create()
pthread_setspecific()

.. and do perror(3) on failure. Not many reasons of failure exist, but I think
it is worth the effort to help debugging in future.

[Primiano Tucci (use gerrit), 2016/04/15 12:51:07]

Went for CHECK. perror doesn't really help on android due to the lack of stdio
(unless running an executable)

+    g_tls_slot_being_initialized = false;
+}
 
 // Returns light-weight process ID. On Linux, this is a system-wide unique
 // thread id.
@@ -163,8 +181,11 @@ class Thread {
     // Disable logging on this thread. Although this routine is not instrumented
     // (cygprofile.gyp provides that), the called routines are and thus will
     // call instrumentation.
-    CHECK(g_tls_log == NULL);  // Must be 0 as this is a new thread.
-    g_tls_log = kMagicBeingConstructed;
+    pthread_once(&g_tls_slot_initializer_once, TLSSlotInitializer);
+    ThreadLog* thread_log = reinterpret_cast<ThreadLog*>(
+        pthread_getspecific(g_tls_slot));
+    CHECK(thread_log == NULL);  // Must be 0 as this is a new thread.
+    pthread_setspecific(g_tls_slot, kMagicBeingConstructed);
 
     Thread* const instance = reinterpret_cast<Thread*>(data);
     instance->thread_callback_.Run();
@@ -199,7 +220,7 @@ ThreadLog::ThreadLog(const FlushCallback& flush_callback)
 }
 
 ThreadLog::~ThreadLog() {
-  g_tls_log = NULL;
+  pthread_setspecific(g_tls_slot, NULL);
 }
 
 void ThreadLog::AddEntry(void* address) {
@@ -358,16 +379,24 @@ void __cyg_profile_func_exit(void* this_fn, void* call_site)
     __attribute__((no_instrument_function));
 
 void __cyg_profile_func_enter(void* this_fn, void* callee_unused) {
-  if (g_tls_log == NULL) {
-    g_tls_log = kMagicBeingConstructed;
-    ThreadLog* new_log = new ThreadLog();
-    CHECK(new_log);
-    g_logs_manager.Pointer()->AddLog(base::WrapUnique(new_log));
-    g_tls_log = new_log;
+  // Avoid re-entrancy while initializing the TLS slot (once per process).
+  if (g_tls_slot_being_initialized)
+    return;
+
+  pthread_once(&g_tls_slot_initializer_once, TLSSlotInitializer);
+  ThreadLog* thread_log = reinterpret_cast<ThreadLog*>(
+      pthread_getspecific(g_tls_slot));
+
+  if (thread_log == NULL) {
+    pthread_setspecific(g_tls_slot, kMagicBeingConstructed);
+    thread_log = new ThreadLog();
+    CHECK(thread_log);
+    g_logs_manager.Pointer()->AddLog(base::WrapUnique(thread_log));
+    pthread_setspecific(g_tls_slot, thread_log);
   }
 
-  if (g_tls_log != kMagicBeingConstructed)
-    g_tls_log->AddEntry(this_fn);
+  if (thread_log != kMagicBeingConstructed)
+    thread_log->AddEntry(this_fn);
 }
 
 void __cyg_profile_func_exit(void* this_fn, void* call_site) {}