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..af0a2a73a2ab494cc4df1dd3b52f585139d8c984 100644
--- a/tools/cygprofile/cygprofile.cc
+++ b/tools/cygprofile/cygprofile.cc
@@ -51,7 +51,27 @@ 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 re-entratively.

[pasko, 2016/04/15 13:00:47]

nit: s/read re-entratively/read in a re-entrant way/

0.1% easier to read for, at least for me

[Primiano Tucci (use gerrit), 2016/04/15 13:06:08]

Done.

+// This variable is written by one thread only, which is the first thread that
+// happens to run the TLSSlotInitializer(). In practice this will happen very
+// early in the startup process, as soon as the first instrumented function is
+// called.
+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;
+    CHECK_EQ(0, pthread_key_create(&g_tls_slot, NULL));

[pasko, 2016/04/15 13:00:47]

let's do a PCHECK(pthread_key_create(&g_tls_slot, NULL))

[pasko, 2016/04/15 13:03:59]

plz disregard this (it returns zero on success, and I thought it's vice versa)

[Primiano Tucci (use gerrit), 2016/04/15 13:06:08]

Done.

[Primiano Tucci (use gerrit), 2016/04/15 13:06:08]

Done.

+    g_tls_slot_being_initialized = false;
+}
 
 // Returns light-weight process ID. On Linux, this is a system-wide unique
 // thread id.
@@ -163,8 +183,11 @@ 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.
+    CHECK_EQ(0, pthread_setspecific(g_tls_slot, kMagicBeingConstructed));
 
     Thread* const instance = reinterpret_cast<Thread*>(data);
     instance->thread_callback_.Run();
@@ -199,7 +222,7 @@ ThreadLog::ThreadLog(const FlushCallback& flush_callback)
 }
 
 ThreadLog::~ThreadLog() {
-  g_tls_log = NULL;
+  CHECK_EQ(0, pthread_setspecific(g_tls_slot, NULL));
 }
 
 void ThreadLog::AddEntry(void* address) {
@@ -358,16 +381,24 @@ 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) {
+    CHECK_EQ(0, pthread_setspecific(g_tls_slot, kMagicBeingConstructed));
+    thread_log = new ThreadLog();
+    CHECK(thread_log);
+    g_logs_manager.Pointer()->AddLog(base::WrapUnique(thread_log));
+    CHECK_EQ(0, 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) {}