Fix race in TestExitDuringStep and unify pseudo_barrier handling

[labath]

Summary

TestExitDuringStep was very rarely hanging on the buildbots. I can't be sure, but I believe this
was because of the fact that it declared its pseudo_barrier variable as "volatile int", which is
not sufficient to guarantee corectness (also, all other tests used atomic variables for this, and
they were passing reliably AFAIK). Besides switching to an atomic variable in this test as well,
I have also took this opportunity to unify all the copies of the pseudo_barrier code to a single
place to reduce the chance of this happening again.

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/break_after_join/main.cpp

 // as success.
 
 #include <atomic>
 #include <chrono>
 #include <thread>
 
 volatile int g_test = 0;
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
-#define do_nothing()  
-
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
 // A barrier to synchronize all the threads.
-std::atomic_int g_barrier1;
+pseudo_barrier_t g_barrier1;
 
 // A barrier to keep the threads from exiting until after the breakpoint has
 // been passed.
-std::atomic_int g_barrier2;
+pseudo_barrier_t g_barrier2;
 
 void *
 break_thread_func ()
 {
     // Wait until all the threads are running
     pseudo_barrier_wait(g_barrier1);
 
     // Wait for the join thread to join

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/concurrent_events/main.cpp

 using namespace std;
 
 #include <pthread.h>
 
 #include <signal.h>
 #include <sys/types.h>
 #include <unistd.h>
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
-#define do_nothing()
-
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
 typedef std::vector<std::pair<unsigned, void*(*)(void*)> > action_counts;
 typedef std::vector<pthread_t> thread_vector;
 
-std::atomic_int g_barrier;
+pseudo_barrier_t g_barrier;
 int g_breakpoint = 0;
 int g_sigusr1_count = 0;
 std::atomic_int g_watchme;
 
 struct action_args {
   int delay;
 };
 

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/create_during_step/main.cpp

 //===-- main.cpp ------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // This test is intended to create a situation in which one thread will be
 // created while the debugger is stepping in another thread.
 
 #include <atomic>
 #include <thread>
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
 #define do_nothing()
 
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
-std::atomic_int g_barrier;
+pseudo_barrier_t g_barrier;
 
 volatile int g_thread_created = 0;
 volatile int g_test = 0;
 
 void *
 step_thread_func ()
 {
     g_test = 0;         // Set breakpoint here

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/exit_during_break/main.cpp

 // as success.
 
 #include <atomic>
 #include <chrono>
 #include <thread>
 
 volatile int g_test = 0;
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
-#define do_nothing()  
-
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
 // A barrier to synchronize all the threads except the one that will exit.
-std::atomic_int g_barrier1;
+pseudo_barrier_t g_barrier1;
 
 // A barrier to synchronize all the threads including the one that will exit.
-std::atomic_int g_barrier2;
+pseudo_barrier_t g_barrier2;
 
 // A barrier to keep the first group of threads from exiting until after the
 // breakpoint has been passed.
-std::atomic_int g_barrier3;
+pseudo_barrier_t g_barrier3;
 
 void *
 break_thread_func ()
 {
     // Wait until the entire first group of threads is running
     pseudo_barrier_wait(g_barrier1);
 
     // Wait for the exiting thread to start

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/exit_during_step/main.cpp

 //===-- main.cpp ------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // This test is intended to create a situation in which one thread will exit
 // while the debugger is stepping in another thread.
 
 #include <thread>
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
 #define do_nothing()
 
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
 // A barrier to synchronize thread start.
-volatile int g_barrier;
+pseudo_barrier_t g_barrier;
 
 volatile int g_thread_exited = 0;
 
 volatile int g_test = 0;
 
 void *
 step_thread_func ()
 {

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/multi_break/main.cpp

 // This test is intended to create a situation in which a breakpoint will be
 // hit in two threads at nearly the same moment.  The expected result is that
 // the breakpoint in the second thread will be hit while the breakpoint handler
 // in the first thread is trying to stop all threads.
 
 #include <atomic>
 #include <thread>
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
-#define do_nothing()
-
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
-std::atomic_int g_barrier;
+pseudo_barrier_t g_barrier;
 
 volatile int g_test = 0;
 
 void *
 thread_func ()
 {
     // Wait until both threads are running
     pseudo_barrier_wait(g_barrier);

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/step_out/main.cpp

 //===-- main.cpp ------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // This test is intended to create a situation in which two threads are stopped
 // at a breakpoint and the debugger issues a step-out command.
 
 #include <atomic>
 #include <thread>
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
-#define do_nothing()
-
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
-std::atomic_int g_barrier;
+pseudo_barrier_t g_barrier;
 
 volatile int g_test = 0;
 
 void step_out_of_here() {
   g_test += 5; // Set breakpoint here
 }
 
 void *

lldb/trunk/packages/Python/lldbsuite/test/functionalities/thread/thread_exit/main.cpp

 //===-- main.cpp ------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // This test verifies the correct handling of child thread exits.
 
 #include <atomic>
 #include <thread>
 
-// Note that although hogging the CPU while waiting for a variable to change
-// would be terrible in production code, it's great for testing since it
-// avoids a lot of messy context switching to get multiple threads synchronized.
-#define do_nothing()
-
-#define pseudo_barrier_wait(bar) \
-    --bar;                       \
-    while (bar > 0)              \
-        do_nothing();
-
-#define pseudo_barrier_init(bar, count) (bar = count)
-
-std::atomic_int g_barrier1;
-std::atomic_int g_barrier2;
-std::atomic_int g_barrier3;
+pseudo_barrier_t g_barrier1;
+pseudo_barrier_t g_barrier2;
+pseudo_barrier_t g_barrier3;
 
 void *
 thread1 ()
 {
     // Synchronize with the main thread.
     pseudo_barrier_wait(g_barrier1);
 
     // Synchronize with the main thread and thread2.

lldb/trunk/packages/Python/lldbsuite/test/make/test_common.h

 
 #endif
 
 #else // not linux
 
 #define lldb_enable_attach()
 
 #endif
+
+#ifdef __cplusplus
+#include <atomic>
+
+// Note that although hogging the CPU while waiting for a variable to change
+// would be terrible in production code, it's great for testing since it
+// avoids a lot of messy context switching to get multiple threads synchronized.
+
+typedef std::atomic<int> pseudo_barrier_t;
+#define pseudo_barrier_wait(barrier)        \
+    do                                      \
+    {                                       \
+        --(barrier);                        \
+        while ((barrier).load() > 0)        \
+            ;                               \
+    } while (0)
+
+#define pseudo_barrier_init(barrier, count) \
+    do                                      \
+    {                                       \
+        (barrier) = (count);                \
+    } while (0)
+#endif // __cplusplus