ART: Rewrite Runtime fault message to be lock-free
To avoid the lock in a general header, rewrite the fault message
(that is almost unused) to be lock-free. Store the string as a
heap object owned by Runtime.
Bug: 119869270
Test: mmma art
Test: m test-art-host
Change-Id: Ib1e027a1543c46d25953119f05792f0e874d6a3d
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 84526f3..d53cc07 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -234,8 +234,7 @@
class_linker_(nullptr),
signal_catcher_(nullptr),
java_vm_(nullptr),
- fault_message_lock_("Fault message lock"),
- fault_message_(""),
+ fault_message_(nullptr),
threads_being_born_(0),
shutdown_cond_(new ConditionVariable("Runtime shutdown", *Locks::runtime_shutdown_lock_)),
shutting_down_(false),
@@ -2367,8 +2366,27 @@
}
void Runtime::SetFaultMessage(const std::string& message) {
- MutexLock mu(Thread::Current(), fault_message_lock_);
- fault_message_ = message;
+ std::string* new_msg = new std::string(message);
+ std::string* cur_msg = fault_message_.exchange(new_msg);
+ delete cur_msg;
+}
+
+std::string Runtime::GetFaultMessage() {
+ // Retrieve the message. Temporarily replace with null so that SetFaultMessage will not delete
+ // the string in parallel.
+ std::string* cur_msg = fault_message_.exchange(nullptr);
+
+ // Make a copy of the string.
+ std::string ret = cur_msg == nullptr ? "" : *cur_msg;
+
+ // Put the message back if it hasn't been updated.
+ std::string* null_str = nullptr;
+ if (!fault_message_.compare_exchange_strong(null_str, cur_msg)) {
+ // Already replaced.
+ delete cur_msg;
+ }
+
+ return ret;
}
void Runtime::AddCurrentRuntimeFeaturesAsDex2OatArguments(std::vector<std::string>* argv)