Convert futex to cond wait. (3cdbfdce) · Commits · e / os / android_system_core

libbacktrace/Android.mk

+4 −0

Original line number	Diff line number	Diff line
		@@ -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

libbacktrace/BacktraceThread.cpp

+33 −16

Original line number	Diff line number	Diff line
		@@ -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.

libbacktrace/BacktraceThread.h

+7 −3

Original line number	Diff line number	Diff line
		@@ -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_;

libbacktrace/backtrace_test.cpp

+12 −5

Original line number	Diff line number	Diff line
		@@ -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);