Convert futex to cond wait.

Switch to the better supported pthread_cond to handle the Wait/Wake
functions.

Also, increase the number of simultaneous threads in the thread tests.

Bug: 18381207

(cherry picked from commit db44538387b08f367fc2419653639866f4c2fbd6)

Change-Id: Id326a7a7b92cb61573def3f761597c40f3ef2f4b

4 files changed, 56 insertions, 24 deletions

diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index 01b4f4d15..f2f71f93c 100755
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -64,6 +64,10 @@ libbacktrace_shared_libraries_host := \
 libbacktrace_static_libraries_host := \
 	libcutils \
 
+libbacktrace_ldlibs_host := \
+	-lpthread \
+	-lrt \
+
 module := libbacktrace
 module_tag := optional
 build_type := target
diff --git a/libbacktrace/BacktraceThread.cpp b/libbacktrace/BacktraceThread.cpp
index b47cd2ad2..439cc3bde 100644
--- a/libbacktrace/BacktraceThread.cpp
+++ b/libbacktrace/BacktraceThread.cpp
@@ -17,14 +17,15 @@
 #include <errno.h>
 #include <inttypes.h>
 #include <limits.h>
-#include <linux/futex.h>
 #include <pthread.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/syscall.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <ucontext.h>
+#include <unistd.h>
 
 #include <cutils/atomic.h>
 
@@ -32,10 +33,6 @@
 #include "BacktraceThread.h"
 #include "thread_utils.h"
 
-static inline int futex(volatile int* uaddr, int op, int val, const struct timespec* ts, volatile int* uaddr2, int val3) {
-  return syscall(__NR_futex, uaddr, op, val, ts, uaddr2, val3);
-}
-
 //-------------------------------------------------------------------------
 // ThreadEntry implementation.
 //-------------------------------------------------------------------------
@@ -45,7 +42,14 @@ pthread_mutex_t ThreadEntry::list_mutex_ = PTHREAD_MUTEX_INITIALIZER;
 // Assumes that ThreadEntry::list_mutex_ has already been locked before
 // creating a ThreadEntry object.
 ThreadEntry::ThreadEntry(pid_t pid, pid_t tid)
-    : pid_(pid), tid_(tid), futex_(0), ref_count_(1), mutex_(PTHREAD_MUTEX_INITIALIZER), next_(ThreadEntry::list_), prev_(NULL) {
+    : pid_(pid), tid_(tid), ref_count_(1), mutex_(PTHREAD_MUTEX_INITIALIZER),
+      wait_mutex_(PTHREAD_MUTEX_INITIALIZER), wait_value_(0),
+      next_(ThreadEntry::list_), prev_(NULL) {
+  pthread_condattr_t attr;
+  pthread_condattr_init(&attr);
+  pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
+  pthread_cond_init(&wait_cond_, &attr);
+
   // Add ourselves to the list.
   if (ThreadEntry::list_) {
     ThreadEntry::list_->prev_ = this;
@@ -99,22 +103,35 @@ ThreadEntry::~ThreadEntry() {
 
   next_ = NULL;
   prev_ = NULL;
+
+  pthread_cond_destroy(&wait_cond_);
 }
 
 void ThreadEntry::Wait(int value) {
   timespec ts;
-  ts.tv_sec = 10;
-  ts.tv_nsec = 0;
-  errno = 0;
-  futex(&futex_, FUTEX_WAIT, value, &ts, NULL, 0);
-  if (errno != 0 && errno != EWOULDBLOCK) {
-    BACK_LOGW("futex wait failed, futex = %d: %s", futex_, strerror(errno));
+  if (clock_gettime(CLOCK_MONOTONIC, &ts) == -1) {
+    BACK_LOGW("clock_gettime failed: %s", strerror(errno));
+    abort();
   }
+  ts.tv_sec += 10;
+
+  pthread_mutex_lock(&wait_mutex_);
+  while (wait_value_ != value) {
+    int ret = pthread_cond_timedwait(&wait_cond_, &wait_mutex_, &ts);
+    if (ret != 0) {
+      BACK_LOGW("pthread_cond_timedwait failed: %s", strerror(ret));
+      break;
+    }
+  }
+  pthread_mutex_unlock(&wait_mutex_);
 }
 
 void ThreadEntry::Wake() {
-  futex_++;
-  futex(&futex_, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
+  pthread_mutex_lock(&wait_mutex_);
+  wait_value_++;
+  pthread_mutex_unlock(&wait_mutex_);
+
+  pthread_cond_signal(&wait_cond_);
 }
 
 void ThreadEntry::CopyUcontextFromSigcontext(void* sigcontext) {
@@ -142,7 +159,7 @@ static void SignalHandler(int, siginfo_t*, void* sigcontext) {
 
   // Pause the thread until the unwind is complete. This avoids having
   // the thread run ahead causing problems.
-  entry->Wait(1);
+  entry->Wait(2);
 
   ThreadEntry::Remove(entry);
 }
@@ -194,7 +211,7 @@ bool BacktraceThread::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
   }
 
   // Wait for the thread to get the ucontext.
-  entry->Wait(0);
+  entry->Wait(1);
 
   // After the thread has received the signal, allow other unwinders to
   // continue.
diff --git a/libbacktrace/BacktraceThread.h b/libbacktrace/BacktraceThread.h
index ff3e9f3f4..99a863878 100644
--- a/libbacktrace/BacktraceThread.h
+++ b/libbacktrace/BacktraceThread.h
@@ -48,8 +48,10 @@ public:
 
   inline void Lock() {
     pthread_mutex_lock(&mutex_);
-    // Reset the futex value in case of multiple unwinds of the same thread.
-    futex_ = 0;
+
+    // Always reset the wait value since this could be the first or nth
+    // time this entry is locked.
+    wait_value_ = 0;
   }
 
   inline void Unlock() {
@@ -66,9 +68,11 @@ private:
 
   pid_t pid_;
   pid_t tid_;
-  int futex_;
   int ref_count_;
   pthread_mutex_t mutex_;
+  pthread_mutex_t wait_mutex_;
+  pthread_cond_t wait_cond_;
+  int wait_value_;
   ThreadEntry* next_;
   ThreadEntry* prev_;
   ucontext_t ucontext_;
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index ed6b21112..8002ed6b8 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -51,7 +51,7 @@
 #define NS_PER_SEC              1000000000ULL
 
 // Number of simultaneous dumping operations to perform.
-#define NUM_THREADS  20
+#define NUM_THREADS  40
 
 // Number of simultaneous threads running in our forked process.
 #define NUM_PTRACE_THREADS 5
@@ -486,6 +486,13 @@ TEST(libbacktrace, thread_level_trace) {
   struct sigaction new_action;
   ASSERT_TRUE(sigaction(THREAD_SIGNAL, NULL, &new_action) == 0);
   EXPECT_EQ(cur_action.sa_sigaction, new_action.sa_sigaction);
+  // The SA_RESTORER flag gets set behind our back, so a direct comparison
+  // doesn't work unless we mask the value off. Mips doesn't have this
+  // flag, so skip this on that platform.
+#ifdef SA_RESTORER
+  cur_action.sa_flags &= ~SA_RESTORER;
+  new_action.sa_flags &= ~SA_RESTORER;
+#endif
   EXPECT_EQ(cur_action.sa_flags, new_action.sa_flags);
 }
 
@@ -583,7 +590,7 @@ TEST(libbacktrace, thread_multiple_dump) {
 
   // Wait for tids to be set.
   for (std::vector<thread_t>::iterator it = runners.begin(); it != runners.end(); ++it) {
-    ASSERT_TRUE(WaitForNonZero(&it->state, 10));
+    ASSERT_TRUE(WaitForNonZero(&it->state, 30));
   }
 
   // Start all of the dumpers at once, they will spin until they are signalled
@@ -602,7 +609,7 @@ TEST(libbacktrace, thread_multiple_dump) {
   android_atomic_acquire_store(1, &dump_now);
 
   for (size_t i = 0; i < NUM_THREADS; i++) {
-    ASSERT_TRUE(WaitForNonZero(&dumpers[i].done, 10));
+    ASSERT_TRUE(WaitForNonZero(&dumpers[i].done, 30));
 
     // Tell the runner thread to exit its infinite loop.
     android_atomic_acquire_store(0, &runners[i].state);
@@ -625,7 +632,7 @@ TEST(libbacktrace, thread_multiple_dump_same_thread) {
   ASSERT_TRUE(pthread_create(&runner.threadId, &attr, ThreadMaxRun, &runner) == 0);
 
   // Wait for tids to be set.
-  ASSERT_TRUE(WaitForNonZero(&runner.state, 10));
+  ASSERT_TRUE(WaitForNonZero(&runner.state, 30));
 
   // Start all of the dumpers at once, they will spin until they are signalled
   // to begin their dump run.
@@ -645,7 +652,7 @@ TEST(libbacktrace, thread_multiple_dump_same_thread) {
   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(WaitForNonZero(&dumpers[i].done, 30));
 
     ASSERT_TRUE(dumpers[i].backtrace != NULL);
     VerifyMaxDump(dumpers[i].backtrace);