Wrote my AIO

POSIX asynchronous I/O is very sub-optimal. They create threads, dynamically allocate memory, and invoke a lot of system calls (which set the signal mask, priority, and more). Additional locks are also possible (if the AIO is using someone else). Moreover, they are not portable.
PlatformLab · Dec 2, 2020 · bea4aaf · bea4aaf
1 parent 137992f
commit bea4aaf
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Showing 4 changed files with 205 additions and 99 deletions.
diff --git a/runtime/DoubleBuffer.h b/runtime/DoubleBuffer.h
@@ -0,0 +1,112 @@
+
+#pragma once
+#include <condition_variable>
+#include <cstdio>
+#include <cstdlib>
+#include <memory>
+#include <mutex>
+
+#include <unistd.h>
+
+#include "Config.h"
+#include "Portability.h"
+
+class DoubleBuffer
+{
+    struct Deleter {
+        void operator()(char *__ptr) const { free(__ptr); }
+    };
+
+    using MemPtrT = std::unique_ptr<char, Deleter>;
+
+    static MemPtrT allocateMemory()
+    {
+        char *tmp;
+        int err = posix_memalign(reinterpret_cast<void **>(&tmp), 512,
+                                 NanoLogConfig::OUTPUT_BUFFER_SIZE);
+        if (err) {
+            perror(
+                "The NanoLog system was not able to allocate enough memory "
+                "to support its operations. Quitting...\r\n");
+            std::exit(-1);
+        }
+        return MemPtrT{tmp};
+    };
+
+    static char *accessOnce(const MemPtrT &ptr)
+    {
+        NANOLOG_READ_WRITE_BARRIER;
+        return ptr.get();
+    }
+
+    MemPtrT freeBuffer;
+    MemPtrT compressingBuffer;
+    MemPtrT writeBuffer;
+    unsigned size;
+    int errorCode;
+
+    std::condition_variable condition;
+    std::mutex mutex;
+
+public:
+    DoubleBuffer()
+        : freeBuffer(allocateMemory()),
+          compressingBuffer(allocateMemory()),
+          writeBuffer(nullptr),
+          size(0),
+          errorCode(0),
+          condition(),
+          mutex(){};
+
+    char *getCompressingBuffer() noexcept { return compressingBuffer.get(); }
+
+    bool writeInProgress() const { return accessOnce(freeBuffer) == nullptr; }
+
+    int swapBuffer(unsigned count) noexcept
+    {
+        while (accessOnce(writeBuffer) != nullptr) {}
+
+        {
+            std::unique_lock<std::mutex> lock(mutex);
+            size = count;
+            std::swap(writeBuffer, compressingBuffer);
+            if (freeBuffer == nullptr) {
+                condition.wait(lock, [this]() { return freeBuffer != nullptr; });
+            } else {
+                condition.notify_one();
+            }
+            std::swap(freeBuffer, compressingBuffer);
+            return errorCode;
+        }
+    }
+
+    void writeToFile(int file) noexcept
+    {
+        unsigned tmp_size = 0;
+        MemPtrT tmp_ptr = nullptr;
+
+        {
+            std::unique_lock<std::mutex> lock(mutex);
+            condition.wait(lock, [this]() { return writeBuffer != nullptr; });
+            tmp_size = size;
+            std::swap(writeBuffer, tmp_ptr);
+        }
+
+        int res = 0;
+        if (tmp_size != 0) {
+            res = write(file, tmp_ptr.get(), tmp_size);
+            res = (res < 0) ? errno : 0;
+        }
+
+        while (accessOnce(freeBuffer) != nullptr) {}
+
+        {
+            std::unique_lock<std::mutex> lock(mutex);
+            errorCode = res;
+            std::swap(freeBuffer, tmp_ptr);
+            if (compressingBuffer == nullptr) {
+                condition.notify_one();
+            }
+        }
+    }
+};
diff --git a/runtime/Portability.h b/runtime/Portability.h
@@ -49,4 +49,12 @@
 #define NANOLOG_PRINTF_FORMAT_ATTR(string_index, first_to_check)
 #endif
 
+#if defined(_MSC_VER)
+extern "C" void _ReadWriteBarrier(void);
+#pragma intrinsic(_ReadWriteBarrier)
+#define NANOLOG_READ_WRITE_BARRIER _ReadWriteBarrier()
+#elif defined(__GNUC__)
+#define NANOLOG_READ_WRITE_BARRIER __sync_synchronize()
+#endif
+
 #endif /* NANOLOG_PORTABILITY_H */
diff --git a/runtime/RuntimeLogger.cc b/runtime/RuntimeLogger.cc
@@ -43,14 +43,13 @@ RuntimeLogger::RuntimeLogger()
         , compressionThread()
         , hasOutstandingOperation(false)
         , compressionThreadShouldExit(false)
+        , writerThreadShouldExit(false)
         , syncStatus(SYNC_COMPLETED)
         , condMutex()
         , workAdded()
         , hintSyncCompleted()
         , outputFd(-1)
-        , aioCb()
-        , compressingBuffer(nullptr)
-        , outputDoubleBuffer(nullptr)
+        , buffer()
         , currentLogLevel(NOTICE)
         , cycleAtThreadStart(0)
         , cyclesAtLastAIOStart(0)
@@ -82,26 +81,9 @@ RuntimeLogger::RuntimeLogger()
         std::exit(-1);
     }
 
-    memset(&aioCb, 0, sizeof(aioCb));
-
-    int err = posix_memalign(reinterpret_cast<void **>(&compressingBuffer),
-                             512, NanoLogConfig::OUTPUT_BUFFER_SIZE);
-    if (err) {
-        perror("The NanoLog system was not able to allocate enough memory "
-                       "to support its operations. Quitting...\r\n");
-        std::exit(-1);
-    }
-
-    err = posix_memalign(reinterpret_cast<void **>(&outputDoubleBuffer),
-                         512, NanoLogConfig::OUTPUT_BUFFER_SIZE);
-    if (err) {
-        perror("The NanoLog system was not able to allocate enough memory "
-                       "to support its operations. Quitting...\r\n");
-        std::exit(-1);
-    }
-
 #ifndef BENCHMARK_DISCARD_ENTRIES_AT_STAGINGBUFFER
     compressionThread = std::thread(&RuntimeLogger::compressionThreadMain, this);
+    writerThread = std::thread(&RuntimeLogger::writerThreadMain, this);
 #endif
 }
 
@@ -116,19 +98,16 @@ RuntimeLogger::~RuntimeLogger() {
         nanoLogSingleton.workAdded.notify_all();
     }
 
+    // Stop the writer thread completely
+    writerThreadShouldExit = true;
+    buffer.swapBuffer(0);
+    writerThread.join();
+
     if (nanoLogSingleton.compressionThread.joinable())
         nanoLogSingleton.compressionThread.join();
 
-    // Free all the data structures
-    if (compressingBuffer) {
-        free(compressingBuffer);
-        compressingBuffer = nullptr;
-    }
-
-    if (outputDoubleBuffer) {
-        free(outputDoubleBuffer);
-        outputDoubleBuffer = nullptr;
-    }
+    if (nanoLogSingleton.writerThread.joinable())
+        nanoLogSingleton.writerThread.join();
 
     if (outputFd > 0)
         close(outputFd);
@@ -314,8 +293,8 @@ RuntimeLogger::preallocate() {
 }
 
 /**
-* Main compression thread that handles scanning through the StagingBuffers,
-* compressing log entries, and outputting a compressed log file.
+* Main compression thread that handles scanning through the StagingBuffers and
+* compressing log entries.
 */
 void
 RuntimeLogger::compressionThreadMain() {
@@ -329,7 +308,7 @@ RuntimeLogger::compressionThreadMain() {
     cycleAtThreadStart = cyclesAwakeStart;
 
     // Manages the state associated with compressing log messages
-    Log::Encoder encoder(compressingBuffer, NanoLogConfig::OUTPUT_BUFFER_SIZE);
+    Log::Encoder encoder(buffer.getCompressingBuffer(), NanoLogConfig::OUTPUT_BUFFER_SIZE);
 
     // Indicates whether a compression operation failed or not due
     // to insufficient space in the outputBuffer
@@ -502,51 +481,35 @@ RuntimeLogger::compressionThreadMain() {
         }
 
         if (hasOutstandingOperation) {
-            if (aio_error(&aioCb) == EINPROGRESS) {
-                const struct aiocb *const aiocb_list[] = {&aioCb};
-                if (outputBufferFull) {
-                    // If the output buffer is full and we're not done,
-                    // wait for completion
-                    cyclesActive += PerfUtils::Cycles::rdtsc() - cyclesAwakeStart;
-                    int err = aio_suspend(aiocb_list, 1, NULL);
+            if (buffer.writeInProgress() && !outputBufferFull) {
+                // If there's no new data, go to sleep.
+                if (bytesConsumedThisIteration == 0 &&
+                    NanoLogConfig::POLL_INTERVAL_DURING_IO_US > 0)
+                {
+                    std::unique_lock<std::mutex> lock(condMutex);
+                    cyclesActive += PerfUtils::Cycles::rdtsc() -
+                                   cyclesAwakeStart;
+                    workAdded.wait_for(lock, std::chrono::microseconds(
+                            NanoLogConfig::POLL_INTERVAL_DURING_IO_US));
                     cyclesAwakeStart = PerfUtils::Cycles::rdtsc();
-                    if (err != 0)
-                        perror("LogCompressor's Posix AIO "
-                                       "suspend operation failed");
-                } else {
-                    // If there's no new data, go to sleep.
-                    if (bytesConsumedThisIteration == 0 &&
-                        NanoLogConfig::POLL_INTERVAL_DURING_IO_US > 0)
-                    {
-                        std::unique_lock<std::mutex> lock(condMutex);
-                        cyclesActive += PerfUtils::Cycles::rdtsc() -
-                                       cyclesAwakeStart;
-                        workAdded.wait_for(lock, std::chrono::microseconds(
-                                NanoLogConfig::POLL_INTERVAL_DURING_IO_US));
-                        cyclesAwakeStart = PerfUtils::Cycles::rdtsc();
-                    }
-
-                    if (aio_error(&aioCb) == EINPROGRESS)
-                        continue;
                 }
-            }
-
-            // Finishing up the IO
-            int err = aio_error(&aioCb);
-            ssize_t ret = aio_return(&aioCb);
 
-            if (err != 0) {
-                fprintf(stderr, "LogCompressor's POSIX AIO failed"
-                        " with %d: %s\r\n", err, strerror(err));
-            } else if (ret < 0) {
-                perror("LogCompressor's Posix AIO Write failed");
+                if (buffer.writeInProgress())
+                    continue;
             }
-            ++numAioWritesCompleted;
-            hasOutstandingOperation = false;
-            cyclesDiskIO_upperBound += (start - cyclesAtLastAIOStart);
 
             // We've completed an AIO, check if we need to notify
             if (syncStatus == WAITING_ON_AIO) {
+                cyclesActive += PerfUtils::Cycles::rdtsc() - cyclesAwakeStart;
+                int err = buffer.swapBuffer(0);
+                cyclesAwakeStart = PerfUtils::Cycles::rdtsc();
+                if (err != 0)
+                    fprintf(stderr, "LogCompressor's write failed with %d: %s\n",
+                            err, strerror(err));
+
+                ++numAioWritesCompleted;
+                hasOutstandingOperation = false;
+                cyclesDiskIO_upperBound += (start - cyclesAtLastAIOStart);
                 std::unique_lock<std::mutex> lock(nanoLogSingleton.condMutex);
                 if (syncStatus == WAITING_ON_AIO) {
                     syncStatus = SYNC_COMPLETED;
@@ -567,34 +530,49 @@ RuntimeLogger::compressionThreadMain() {
             ssize_t bytesOver = bytesToWrite % 512;
 
             if (bytesOver != 0) {
-                memset(compressingBuffer, 0, 512 - bytesOver);
+                memset(buffer.getCompressingBuffer(), 0, 512 - bytesOver);
                 bytesToWrite = bytesToWrite + 512 - bytesOver;
                 padBytesWritten += (512 - bytesOver);
             }
         }
 
-        aioCb.aio_fildes = outputFd;
-        aioCb.aio_buf = compressingBuffer;
-        aioCb.aio_nbytes = bytesToWrite;
         totalBytesWritten += bytesToWrite;
 
-        cyclesAtLastAIOStart = PerfUtils::Cycles::rdtsc();
-        if (aio_write(&aioCb) == -1)
-            fprintf(stderr, "Error at aio_write(): %s\n", strerror(errno));
+        uint64_t tmp = PerfUtils::Cycles::rdtsc();
+        int err = buffer.swapBuffer(bytesToWrite);
+
+        if (hasOutstandingOperation) {
+            cyclesActive += tmp - cyclesAwakeStart;
+            cyclesAwakeStart = PerfUtils::Cycles::rdtsc();
+            if (err != 0)
+                fprintf(stderr, "LogCompressor's write failed with %d: %s\n", err,
+                        strerror(err));
 
-        hasOutstandingOperation = true;
+            ++numAioWritesCompleted;
+            cyclesDiskIO_upperBound += (start - cyclesAtLastAIOStart);
+        }
 
-        // Swap buffers
-        encoder.swapBuffer(outputDoubleBuffer,
+        cyclesAtLastAIOStart = tmp;
+        hasOutstandingOperation = true;
+        encoder.swapBuffer(buffer.getCompressingBuffer(),
                            NanoLogConfig::OUTPUT_BUFFER_SIZE);
-        std::swap(outputDoubleBuffer, compressingBuffer);
         outputBufferFull = false;
     }
 
     cycleAtThreadStart = 0;
     cyclesActive += PerfUtils::Cycles::rdtsc() - cyclesAwakeStart;
 }
 
+/**
+* Main writer thread that outputting a compressed log file.
+*/
+void
+RuntimeLogger::writerThreadMain() {
+    while (!writerThreadShouldExit) {
+        buffer.writeToFile(outputFd);
+    }
+}
+
 // Documentation in NanoLog.h
 void
 RuntimeLogger::setLogFile_internal(const char *filename) {
@@ -625,18 +603,28 @@ RuntimeLogger::setLogFile_internal(const char *filename) {
         workAdded.notify_all();
     }
 
+    // Stop the writer thread completely
+    writerThreadShouldExit = true;
+    buffer.swapBuffer(0);
+    writerThread.join();
+
     if (compressionThread.joinable())
         compressionThread.join();
 
+    if (writerThread.joinable())
+        writerThread.join();
+
     if (outputFd > 0)
         close(outputFd);
     outputFd = newFd;
 
     // Relaunch thread
     nextInvocationIndexToBePersisted = 0; // Reset the dictionary
     compressionThreadShouldExit = false;
+    writerThreadShouldExit = false;
 #ifndef BENCHMARK_DISCARD_ENTRIES_AT_STAGINGBUFFER
     compressionThread = std::thread(&RuntimeLogger::compressionThreadMain, this);
+    writerThread = std::thread(&RuntimeLogger::writerThreadMain, this);
 #endif
 }