diff options
| -rw-r--r-- | libcorkscrew/backtrace.c | 64 |
1 files changed, 52 insertions, 12 deletions
diff --git a/libcorkscrew/backtrace.c b/libcorkscrew/backtrace.c index f9a49ec..857b741 100644 --- a/libcorkscrew/backtrace.c +++ b/libcorkscrew/backtrace.c @@ -85,9 +85,13 @@ ssize_t unwind_backtrace(backtrace_frame_t* backtrace, size_t ignore_depth, size } #ifdef CORKSCREW_HAVE_ARCH +static const int32_t STATE_DUMPING = -1; +static const int32_t STATE_DONE = -2; +static const int32_t STATE_CANCEL = -3; + static pthread_mutex_t g_unwind_signal_mutex = PTHREAD_MUTEX_INITIALIZER; static volatile struct { - int32_t tid; + int32_t tid_state; const map_info_t* map_info_list; backtrace_frame_t* backtrace; size_t ignore_depth; @@ -96,22 +100,23 @@ static volatile struct { } g_unwind_signal_state; static void unwind_backtrace_thread_signal_handler(int n, siginfo_t* siginfo, void* sigcontext) { - int32_t tid = android_atomic_acquire_load(&g_unwind_signal_state.tid); - if (tid == gettid()) { + if (!android_atomic_acquire_cas(gettid(), STATE_DUMPING, &g_unwind_signal_state.tid_state)) { g_unwind_signal_state.returned_frames = unwind_backtrace_signal_arch( siginfo, sigcontext, g_unwind_signal_state.map_info_list, g_unwind_signal_state.backtrace, g_unwind_signal_state.ignore_depth, g_unwind_signal_state.max_depth); - android_atomic_release_store(-1, &g_unwind_signal_state.tid); + android_atomic_release_store(STATE_DONE, &g_unwind_signal_state.tid_state); } else { ALOGV("Received spurious SIGURG on thread %d that was intended for thread %d.", - gettid(), tid); + gettid(), android_atomic_acquire_load(&g_unwind_signal_state.tid_state)); } } #endif +extern int tgkill(int tgid, int tid, int sig); + ssize_t unwind_backtrace_thread(pid_t tid, backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) { if (tid == gettid()) { @@ -125,7 +130,7 @@ ssize_t unwind_backtrace_thread(pid_t tid, backtrace_frame_t* backtrace, struct sigaction oact; memset(&act, 0, sizeof(act)); act.sa_sigaction = unwind_backtrace_thread_signal_handler; - act.sa_flags = SA_RESTART | SA_SIGINFO; + act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK; sigemptyset(&act.sa_mask); pthread_mutex_lock(&g_unwind_signal_mutex); @@ -138,16 +143,51 @@ ssize_t unwind_backtrace_thread(pid_t tid, backtrace_frame_t* backtrace, g_unwind_signal_state.ignore_depth = ignore_depth; g_unwind_signal_state.max_depth = max_depth; g_unwind_signal_state.returned_frames = 0; - android_atomic_release_store(tid, &g_unwind_signal_state.tid); + android_atomic_release_store(tid, &g_unwind_signal_state.tid_state); - if (kill(tid, SIGURG)) { + // Signal the specific thread that we want to dump. + int32_t tid_state = tid; + if (tgkill(getpid(), tid, SIGURG)) { ALOGV("Failed to send SIGURG to thread %d.", tid); - android_atomic_release_store(-1, &g_unwind_signal_state.tid); } else { - while (android_atomic_acquire_load(&g_unwind_signal_state.tid) == tid) { - ALOGV("Waiting for response from thread %d...", tid); - usleep(1000); + // Wait for the other thread to start dumping the stack, or time out. + int wait_millis = 250; + for (;;) { + tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state); + if (tid_state != tid) { + break; + } + if (wait_millis--) { + ALOGV("Waiting for thread %d to start dumping the stack...", tid); + usleep(1000); + } else { + ALOGV("Timed out waiting for thread %d to start dumping the stack.", tid); + break; + } + } + } + + // Try to cancel the dump if it has not started yet. + if (tid_state == tid) { + if (!android_atomic_acquire_cas(tid, STATE_CANCEL, &g_unwind_signal_state.tid_state)) { + ALOGV("Canceled thread %d stack dump.", tid); + tid_state = STATE_CANCEL; + } else { + tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state); } + } + + // Wait indefinitely for the dump to finish or be canceled. + // We cannot apply a timeout here because the other thread is accessing state that + // is owned by this thread, such as milist. It should not take very + // long to take the dump once started. + while (tid_state == STATE_DUMPING) { + ALOGV("Waiting for thread %d to finish dumping the stack...", tid); + usleep(1000); + tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state); + } + + if (tid_state == STATE_DONE) { frames = g_unwind_signal_state.returned_frames; } |