5 files changed, 257 insertions, 18 deletions

diff --git a/src/common/common_paths.h b/src/common/common_paths.h
index 0a6132dab..d03fca314 100644
--- a/src/common/common_paths.h
+++ b/src/common/common_paths.h
@@ -32,12 +32,15 @@
 #define SDMC_DIR "sdmc"
 #define NAND_DIR "nand"
 #define SYSDATA_DIR "sysdata"
+#define LOG_DIR "log"
 
 // Filenames
 // Files in the directory returned by GetUserPath(D_CONFIG_IDX)
 #define EMU_CONFIG "emu.ini"
 #define DEBUGGER_CONFIG "debugger.ini"
 #define LOGGER_CONFIG "logger.ini"
+// Files in the directory returned by GetUserPath(D_LOGS_IDX)
+#define LOG_FILE "citra_log.txt"
 
 // Sys files
 #define SHARED_FONT "shared_font.bin"
diff --git a/src/common/file_util.cpp b/src/common/file_util.cpp
index 2152e3fea..b9e1fd1f6 100644
--- a/src/common/file_util.cpp
+++ b/src/common/file_util.cpp
@@ -713,6 +713,8 @@ const std::string& GetUserPath(const unsigned int DirIDX, const std::string& new
         paths[D_SDMC_IDX] = paths[D_USER_IDX] + SDMC_DIR DIR_SEP;
         paths[D_NAND_IDX] = paths[D_USER_IDX] + NAND_DIR DIR_SEP;
         paths[D_SYSDATA_IDX] = paths[D_USER_IDX] + SYSDATA_DIR DIR_SEP;
+        // TODO: Put the logs in a better location for each OS
+        paths[D_LOGS_IDX] = paths[D_USER_IDX] + LOG_DIR DIR_SEP;
     }
 
     if (!newPath.empty()) {
@@ -799,8 +801,8 @@ void SplitFilename83(const std::string& filename, std::array<char, 9>& short_nam
 
 IOFile::IOFile() {}
 
-IOFile::IOFile(const std::string& filename, const char openmode[]) {
-    Open(filename, openmode);
+IOFile::IOFile(const std::string& filename, const char openmode[], int flags) {
+    Open(filename, openmode, flags);
 }
 
 IOFile::~IOFile() {
@@ -821,11 +823,16 @@ void IOFile::Swap(IOFile& other) noexcept {
     std::swap(m_good, other.m_good);
 }
 
-bool IOFile::Open(const std::string& filename, const char openmode[]) {
+bool IOFile::Open(const std::string& filename, const char openmode[], int flags) {
     Close();
 #ifdef _WIN32
-    _wfopen_s(&m_file, Common::UTF8ToUTF16W(filename).c_str(),
-              Common::UTF8ToUTF16W(openmode).c_str());
+    if (flags != 0) {
+        m_file = _wfsopen(Common::UTF8ToUTF16W(filename).c_str(),
+                          Common::UTF8ToUTF16W(openmode).c_str(), flags);
+    } else {
+        _wfopen_s(&m_file, Common::UTF8ToUTF16W(filename).c_str(),
+                  Common::UTF8ToUTF16W(openmode).c_str());
+    }
 #else
     m_file = fopen(filename.c_str(), openmode);
 #endif
diff --git a/src/common/file_util.h b/src/common/file_util.h
index fc6b3ea46..5bc7fbf7c 100644
--- a/src/common/file_util.h
+++ b/src/common/file_util.h
@@ -156,7 +156,10 @@ void SplitFilename83(const std::string& filename, std::array<char, 9>& short_nam
 class IOFile : public NonCopyable {
 public:
     IOFile();
-    IOFile(const std::string& filename, const char openmode[]);
+    // flags is used for windows specific file open mode flags, which
+    // allows yuzu to open the logs in shared write mode, so that the file
+    // isn't considered "locked" while yuzu is open and people can open the log file and view it
+    IOFile(const std::string& filename, const char openmode[], int flags = 0);
 
     ~IOFile();
 
@@ -165,7 +168,7 @@ public:
 
     void Swap(IOFile& other) noexcept;
 
-    bool Open(const std::string& filename, const char openmode[]);
+    bool Open(const std::string& filename, const char openmode[], int flags = 0);
     bool Close();
 
     template <typename T>
@@ -220,6 +223,10 @@ public:
         return WriteArray(&object, 1);
     }
 
+    size_t WriteString(const std::string& str) {
+        return WriteArray(str.c_str(), str.length());
+    }
+
     bool IsOpen() const {
         return nullptr != m_file;
     }
diff --git a/src/common/logging/backend.cpp b/src/common/logging/backend.cpp
index c26b20062..242914c6a 100644
--- a/src/common/logging/backend.cpp
+++ b/src/common/logging/backend.cpp
@@ -2,16 +2,145 @@
 // Licensed under GPLv2 or any later version
 // Refer to the license.txt file included.
 
-#include <utility>
+#include <algorithm>
+#include <array>
+#include <chrono>
+#include <condition_variable>
+#include <memory>
+#include <thread>
+#ifdef _WIN32
+#include <share.h> // For _SH_DENYWR
+#else
+#define _SH_DENYWR 0
+#endif
 #include "common/assert.h"
+#include "common/common_funcs.h" // snprintf compatibility define
 #include "common/logging/backend.h"
-#include "common/logging/filter.h"
 #include "common/logging/log.h"
 #include "common/logging/text_formatter.h"
 #include "common/string_util.h"
+#include "common/threadsafe_queue.h"
 
 namespace Log {
 
+/**
+ * Static state as a singleton.
+ */
+class Impl {
+public:
+    static Impl& Instance() {
+        static Impl backend;
+        return backend;
+    }
+
+    Impl(Impl const&) = delete;
+    const Impl& operator=(Impl const&) = delete;
+
+    void PushEntry(Entry e) {
+        std::lock_guard<std::mutex> lock(message_mutex);
+        message_queue.Push(std::move(e));
+        message_cv.notify_one();
+    }
+
+    void AddBackend(std::unique_ptr<Backend> backend) {
+        std::lock_guard<std::mutex> lock(writing_mutex);
+        backends.push_back(std::move(backend));
+    }
+
+    void RemoveBackend(const std::string& backend_name) {
+        std::lock_guard<std::mutex> lock(writing_mutex);
+        auto it = std::remove_if(backends.begin(), backends.end(), [&backend_name](const auto& i) {
+            return !strcmp(i->GetName(), backend_name.c_str());
+        });
+        backends.erase(it, backends.end());
+    }
+
+    const Filter& GetGlobalFilter() const {
+        return filter;
+    }
+
+    void SetGlobalFilter(const Filter& f) {
+        filter = f;
+    }
+
+    Backend* GetBackend(const std::string& backend_name) {
+        auto it = std::find_if(backends.begin(), backends.end(), [&backend_name](const auto& i) {
+            return !strcmp(i->GetName(), backend_name.c_str());
+        });
+        if (it == backends.end())
+            return nullptr;
+        return it->get();
+    }
+
+private:
+    Impl() {
+        backend_thread = std::thread([&] {
+            Entry entry;
+            auto write_logs = [&](Entry& e) {
+                std::lock_guard<std::mutex> lock(writing_mutex);
+                for (const auto& backend : backends) {
+                    backend->Write(e);
+                }
+            };
+            while (true) {
+                std::unique_lock<std::mutex> lock(message_mutex);
+                message_cv.wait(lock, [&] { return !running || message_queue.Pop(entry); });
+                if (!running) {
+                    break;
+                }
+                write_logs(entry);
+            }
+            // Drain the logging queue. Only writes out up to MAX_LOGS_TO_WRITE to prevent a case
+            // where a system is repeatedly spamming logs even on close.
+            constexpr int MAX_LOGS_TO_WRITE = 100;
+            int logs_written = 0;
+            while (logs_written++ < MAX_LOGS_TO_WRITE && message_queue.Pop(entry)) {
+                write_logs(entry);
+            }
+        });
+    }
+
+    ~Impl() {
+        running = false;
+        message_cv.notify_one();
+        backend_thread.join();
+    }
+
+    std::atomic_bool running{true};
+    std::mutex message_mutex, writing_mutex;
+    std::condition_variable message_cv;
+    std::thread backend_thread;
+    std::vector<std::unique_ptr<Backend>> backends;
+    Common::MPSCQueue<Log::Entry> message_queue;
+    Filter filter;
+};
+
+void ConsoleBackend::Write(const Entry& entry) {
+    PrintMessage(entry);
+}
+
+void ColorConsoleBackend::Write(const Entry& entry) {
+    PrintColoredMessage(entry);
+}
+
+// _SH_DENYWR allows read only access to the file for other programs.
+// It is #defined to 0 on other platforms
+FileBackend::FileBackend(const std::string& filename)
+    : file(filename, "w", _SH_DENYWR), bytes_written(0) {}
+
+void FileBackend::Write(const Entry& entry) {
+    // prevent logs from going over the maximum size (in case its spamming and the user doesn't
+    // know)
+    constexpr size_t MAX_BYTES_WRITTEN = 50 * 1024L * 1024L;
+    if (!file.IsOpen() || bytes_written > MAX_BYTES_WRITTEN) {
+        return;
+    }
+    bytes_written += file.WriteString(FormatLogMessage(entry) + '\n');
+    if (entry.log_level >= Level::Error) {
+        file.Flush();
+    }
+}
+
 /// Macro listing all log classes. Code should define CLS and SUB as desired before invoking this.
 #define ALL_LOG_CLASSES()                                                                          \
     CLS(Log)                                                                                       \
@@ -125,20 +254,32 @@ Entry CreateEntry(Class log_class, Level log_level, const char* filename, unsign
     return entry;
 }
 
-static Filter* filter = nullptr;
+void SetGlobalFilter(const Filter& filter) {
+    Impl::Instance().SetGlobalFilter(filter);
+}
+
+void AddBackend(std::unique_ptr<Backend> backend) {
+    Impl::Instance().AddBackend(std::move(backend));
+}
 
-void SetFilter(Filter* new_filter) {
-    filter = new_filter;
+void RemoveBackend(const std::string& backend_name) {
+    Impl::Instance().RemoveBackend(backend_name);
+}
+
+Backend* GetBackend(const std::string& backend_name) {
+    return Impl::Instance().GetBackend(backend_name);
 }
 
 void FmtLogMessageImpl(Class log_class, Level log_level, const char* filename,
                        unsigned int line_num, const char* function, const char* format,
                        const fmt::format_args& args) {
-    if (filter && !filter->CheckMessage(log_class, log_level))
+    auto filter = Impl::Instance().GetGlobalFilter();
+    if (!filter.CheckMessage(log_class, log_level))
         return;
+
     Entry entry =
         CreateEntry(log_class, log_level, filename, line_num, function, fmt::vformat(format, args));
 
-    PrintColoredMessage(entry);
+    Impl::Instance().PushEntry(std::move(entry));
 }
-} // namespace Log
+} // namespace Log
\ No newline at end of file
diff --git a/src/common/logging/backend.h b/src/common/logging/backend.h
index 7e81efb23..57cdf6b2d 100644
--- a/src/common/logging/backend.h
+++ b/src/common/logging/backend.h
@@ -1,13 +1,15 @@
 // Copyright 2014 Citra Emulator Project
 // Licensed under GPLv2 or any later version
 // Refer to the license.txt file included.
-
 #pragma once
 
 #include <chrono>
 #include <cstdarg>
+#include <memory>
 #include <string>
 #include <utility>
+#include "common/file_util.h"
+#include "common/logging/filter.h"
 #include "common/logging/log.h"
 
 namespace Log {
@@ -35,6 +37,80 @@ struct Entry {
 };
 
 /**
+ * Interface for logging backends. As loggers can be created and removed at runtime, this can be
+ * used by a frontend for adding a custom logging backend as needed
+ */
+class Backend {
+public:
+    virtual ~Backend() = default;
+    virtual void SetFilter(const Filter& new_filter) {
+        filter = new_filter;
+    }
+    virtual const char* GetName() const = 0;
+    virtual void Write(const Entry& entry) = 0;
+
+private:
+    Filter filter;
+};
+
+/**
+ * Backend that writes to stderr without any color commands
+ */
+class ConsoleBackend : public Backend {
+public:
+    static const char* Name() {
+        return "console";
+    }
+    const char* GetName() const override {
+        return Name();
+    }
+    void Write(const Entry& entry) override;
+};
+
+/**
+ * Backend that writes to stderr and with color
+ */
+class ColorConsoleBackend : public Backend {
+public:
+    static const char* Name() {
+        return "color_console";
+    }
+
+    const char* GetName() const override {
+        return Name();
+    }
+    void Write(const Entry& entry) override;
+};
+
+/**
+ * Backend that writes to a file passed into the constructor
+ */
+class FileBackend : public Backend {
+public:
+    explicit FileBackend(const std::string& filename);
+
+    static const char* Name() {
+        return "file";
+    }
+
+    const char* GetName() const override {
+        return Name();
+    }
+
+    void Write(const Entry& entry) override;
+
+private:
+    FileUtil::IOFile file;
+    size_t bytes_written;
+};
+
+void AddBackend(std::unique_ptr<Backend> backend);
+
+void RemoveBackend(const std::string& backend_name);
+
+Backend* GetBackend(const std::string& backend_name);
+
+/**
  * Returns the name of the passed log class as a C-string. Subclasses are separated by periods
  * instead of underscores as in the enumeration.
  */
@@ -49,5 +125,10 @@ const char* GetLevelName(Level log_level);
 Entry CreateEntry(Class log_class, Level log_level, const char* filename, unsigned int line_nr,
                   const char* function, std::string message);
 
-void SetFilter(Filter* filter);
-} // namespace Log
+/**
+ * The global filter will prevent any messages from even being processed if they are filtered. Each
+ * backend can have a filter, but if the level is lower than the global filter, the backend will
+ * never get the message
+ */
+void SetGlobalFilter(const Filter& filter);
+} // namespace Log
\ No newline at end of file