Rewrite unwind thread handling.

This new version doesn't require any specialized thread
implementation, it uses the Current implementation to do its job.
In addition, it runs much faster when multiple threads are trying
to unwind at the same time since the global signal lock is held for
only a small amount of time. Even running through the threads one at
a time should be faster since it no longer requires two passes through
the unwound stacks.

The new code now allows multiple simultaneous unwinds of the
same thread.

Finally, add the ability to unwind from a ucontext_t passed in. This
functionality doesn't work for remote unwinds yet.

Change-Id: I4d181d7ca5ffd2acfd1686e668e6d21e36b425cb

1 files changed, 43 insertions, 0 deletions

diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 9744922db..ed6b21112 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -615,6 +615,49 @@ TEST(libbacktrace, thread_multiple_dump) {
   }
 }
 
+TEST(libbacktrace, thread_multiple_dump_same_thread) {
+  pthread_attr_t attr;
+  pthread_attr_init(&attr);
+  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+  thread_t runner;
+  runner.tid = 0;
+  runner.state = 0;
+  ASSERT_TRUE(pthread_create(&runner.threadId, &attr, ThreadMaxRun, &runner) == 0);
+
+  // Wait for tids to be set.
+  ASSERT_TRUE(WaitForNonZero(&runner.state, 10));
+
+  // Start all of the dumpers at once, they will spin until they are signalled
+  // to begin their dump run.
+  int32_t dump_now = 0;
+  // Dump the same thread NUM_THREADS simultaneously.
+  std::vector<dump_thread_t> dumpers(NUM_THREADS);
+  for (size_t i = 0; i < NUM_THREADS; i++) {
+    dumpers[i].thread.tid = runner.tid;
+    dumpers[i].thread.state = 0;
+    dumpers[i].done = 0;
+    dumpers[i].now = &dump_now;
+
+    ASSERT_TRUE(pthread_create(&dumpers[i].thread.threadId, &attr, ThreadDump, &dumpers[i]) == 0);
+  }
+
+  // Start all of the dumpers going at once.
+  android_atomic_acquire_store(1, &dump_now);
+
+  for (size_t i = 0; i < NUM_THREADS; i++) {
+    ASSERT_TRUE(WaitForNonZero(&dumpers[i].done, 100));
+
+    ASSERT_TRUE(dumpers[i].backtrace != NULL);
+    VerifyMaxDump(dumpers[i].backtrace);
+
+    delete dumpers[i].backtrace;
+    dumpers[i].backtrace = NULL;
+  }
+
+  // Tell the runner thread to exit its infinite loop.
+  android_atomic_acquire_store(0, &runner.state);
+}
+
 // This test is for UnwindMaps that should share the same map cursor when
 // multiple maps are created for the current process at the same time.
 TEST(libbacktrace, simultaneous_maps) {