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8269865: Async UL needs to handle ERANGE on exceeding SEM_VALUE_MAX
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Reviewed-by: dholmes, pchilanomate
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Xin Liu committed Jul 14, 2021
1 parent 0f54707 commit 67273ae
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Showing 2 changed files with 20 additions and 14 deletions.
25 changes: 17 additions & 8 deletions src/hotspot/share/logging/logAsyncWriter.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -27,16 +27,17 @@
#include "logging/logFileOutput.hpp"
#include "logging/logHandle.hpp"
#include "runtime/atomic.hpp"
#include "runtime/os.inline.hpp"

class AsyncLogWriter::AsyncLogLocker : public StackObj {
public:
AsyncLogLocker() {
assert(_instance != nullptr, "AsyncLogWriter::_lock is unavailable");
_instance->_lock.wait();
_instance->_lock.lock();
}

~AsyncLogLocker() {
_instance->_lock.signal();
_instance->_lock.unlock();
}
};

Expand All @@ -51,7 +52,8 @@ void AsyncLogWriter::enqueue_locked(const AsyncLogMessage& msg) {
}

_buffer.push_back(msg);
_sem.signal();
_data_available = true;
_lock.notify();
}

void AsyncLogWriter::enqueue(LogFileOutput& output, const LogDecorations& decorations, const char* msg) {
Expand All @@ -75,7 +77,7 @@ void AsyncLogWriter::enqueue(LogFileOutput& output, LogMessageBuffer::Iterator m
}

AsyncLogWriter::AsyncLogWriter()
: _lock(1), _sem(0), _flush_sem(0),
: _flush_sem(0), _lock(), _data_available(false),
_initialized(false),
_stats(17 /*table_size*/) {
if (os::create_thread(this, os::asynclog_thread)) {
Expand Down Expand Up @@ -125,6 +127,7 @@ void AsyncLogWriter::write() {
// append meta-messages of dropped counters
AsyncLogMapIterator dropped_counters_iter(logs);
_stats.iterate(&dropped_counters_iter);
_data_available = false;
}

LinkedListIterator<AsyncLogMessage> it(logs.head());
Expand Down Expand Up @@ -152,9 +155,14 @@ void AsyncLogWriter::write() {

void AsyncLogWriter::run() {
while (true) {
// The value of a semphore cannot be negative. Therefore, the current thread falls asleep
// when its value is zero. It will be waken up when new messages are enqueued.
_sem.wait();
{
AsyncLogLocker locker;

while (!_data_available) {
_lock.wait(0/* no timeout */);
}
}

write();
}
}
Expand Down Expand Up @@ -198,7 +206,8 @@ void AsyncLogWriter::flush() {

// Push directly in-case we are at logical max capacity, as this must not get dropped.
_instance->_buffer.push_back(token);
_instance->_sem.signal();
_instance->_data_available = true;
_instance->_lock.notify();
}

_instance->_flush_sem.wait();
Expand Down
9 changes: 3 additions & 6 deletions src/hotspot/share/logging/logAsyncWriter.hpp
Original file line number Diff line number Diff line change
Expand Up @@ -135,13 +135,10 @@ class AsyncLogWriter : public NonJavaThread {
class AsyncLogLocker;

static AsyncLogWriter* _instance;
// _lock(1) denotes a critional region.
Semaphore _lock;
// _sem is a semaphore whose value denotes how many messages have been enqueued.
// It decreases in AsyncLogWriter::run()
Semaphore _sem;
Semaphore _flush_sem;

// Can't use a Monitor here as we need a low-level API that can be used without Thread::current().
os::PlatformMonitor _lock;
bool _data_available;
volatile bool _initialized;
AsyncLogMap _stats; // statistics for dropped messages
AsyncLogBuffer _buffer;
Expand Down

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