Thread::getTid returns pid_t gettid() after run

This is needed when the parent or any other thread besides the child
needs access to the child's kernel tid.

Change-Id: Ib148505913eb78314cfd76657c30d7b20663dffd

2 files changed, 41 insertions, 5 deletions

diff --git a/libs/utils/Android.mk b/libs/utils/Android.mk
index 544ab744e..24cf5048f 100644
--- a/libs/utils/Android.mk
+++ b/libs/utils/Android.mk
@@ -98,7 +98,8 @@ endif
 
 LOCAL_C_INCLUDES += \
 		external/zlib \
-		external/icu4c/common
+		external/icu4c/common \
+		bionic/libc/private
 
 LOCAL_LDLIBS += -lpthread
 
@@ -114,7 +115,10 @@ include $(BUILD_SHARED_LIBRARY)
 
 ifeq ($(TARGET_OS),linux)
 include $(CLEAR_VARS)
-LOCAL_C_INCLUDES += external/zlib external/icu4c/common
+LOCAL_C_INCLUDES += \
+		external/zlib \
+		external/icu4c/common \
+		bionic/libc/private
 LOCAL_LDLIBS := -lrt -ldl -lpthread
 LOCAL_MODULE := libutils
 LOCAL_SRC_FILES := $(commonSources) BackupData.cpp BackupHelpers.cpp
diff --git a/libs/utils/Threads.cpp b/libs/utils/Threads.cpp
index e343c6235..ab207f565 100644
--- a/libs/utils/Threads.cpp
+++ b/libs/utils/Threads.cpp
@@ -34,6 +34,9 @@
 # include <pthread.h>
 # include <sched.h>
 # include <sys/resource.h>
+#ifdef HAVE_ANDROID_OS
+# include <bionic_pthread.h>
+#endif
 #elif defined(HAVE_WIN32_THREADS)
 # include <windows.h>
 # include <stdint.h>
@@ -86,7 +89,7 @@ struct thread_data_t {
     char *          threadName;
 
     // we use this trampoline when we need to set the priority with
-    // nice/setpriority.
+    // nice/setpriority, and name with prctl.
     static int trampoline(const thread_data_t* t) {
         thread_func_t f = t->entryFunction;
         void* u = t->userData;
@@ -141,8 +144,13 @@ int androidCreateRawThreadEtc(android_thread_func_t entryFunction,
 
 #ifdef HAVE_ANDROID_OS  /* valgrind is rejecting RT-priority create reqs */
     if (threadPriority != PRIORITY_DEFAULT || threadName != NULL) {
-        // We could avoid the trampoline if there was a way to get to the
-        // android_thread_id_t (pid) from pthread_t
+        // Now that the pthread_t has a method to find the associated
+        // android_thread_id_t (pid) from pthread_t, it would be possible to avoid
+        // this trampoline in some cases as the parent could set the properties
+        // for the child.  However, there would be a race condition because the
+        // child becomes ready immediately, and it doesn't work for the name.
+        // prctl(PR_SET_NAME) only works for self; prctl(PR_SET_THREAD_NAME) was
+        // proposed but not yet accepted.
         thread_data_t* t = new thread_data_t;
         t->priority = threadPriority;
         t->threadName = threadName ? strdup(threadName) : NULL;
@@ -178,6 +186,13 @@ int androidCreateRawThreadEtc(android_thread_func_t entryFunction,
     return 1;
 }
 
+#ifdef HAVE_ANDROID_OS
+static pthread_t android_thread_id_t_to_pthread(android_thread_id_t thread)
+{
+    return (pthread_t) thread;
+}
+#endif
+
 android_thread_id_t androidGetThreadId()
 {
     return (android_thread_id_t)pthread_self();
@@ -909,6 +924,23 @@ status_t Thread::join()
     return mStatus;
 }
 
+#ifdef HAVE_ANDROID_OS
+pid_t Thread::getTid() const
+{
+    // mTid is not defined until the child initializes it, and the caller may need it earlier
+    Mutex::Autolock _l(mLock);
+    pid_t tid;
+    if (mRunning) {
+        pthread_t pthread = android_thread_id_t_to_pthread(mThread);
+        tid = __pthread_gettid(pthread);
+    } else {
+        ALOGW("Thread (this=%p): getTid() is undefined before run()", this);
+        tid = -1;
+    }
+    return tid;
+}
+#endif
+
 bool Thread::exitPending() const
 {
     Mutex::Autolock _l(mLock);