Logging system in chromium

chromium The logging in actually uses libglog

ubuntu Lower installation libglog:  sudo apt install libgoogle-glog-dev

libglog Examples of use ：

#include <iostream>
#include "glog/logging.h"   // glog  The header file 
using namespace std;
int main(int argc, char** argv) {
  google::InitGoogleLogging(argv[0]);    //  initialization 
  // FLAGS_log_dir=".";   // Set up log Catalog , Print to by default "/tmp/ The program name .INFO"
  LOG(INFO) << "hello glog";     //  Print log：“hello glog.   Be similar to C++ stream.
}

Compile command ： g++ main.cpp -lglog

chromium in logging Log system initialization ：

void InitLogging() {
  base::FilePath log_filename;
  PathService::Get(base::DIR_EXE, &log_filename);
  log_filename = log_filename.AppendASCII("content_shell.log"); // Get the log file under the current executable directory content_shell.log
  logging::LoggingSettings settings;
  settings.logging_dest = logging::LOG_TO_ALL; // Logs are saved to file and system modal logs 
  settings.log_file = log_filename.value().c_str(); // Specify log files content_shell.log
  settings.delete_old = logging::DELETE_OLD_LOG_FILE; // Delete old logs 
  logging::InitLogging(settings);
  logging::SetLogItems(true, true, true, true); // Log save item :  process ID、 Threads ID、 Time stamp 、tick Count 
}    

The log level ：

typedef int LogSeverity;
const LogSeverity LOG_VERBOSE = -1;  // This is level 1 verbosity
// Note: the log severities are used to index into the array of names, see log_severity_names.
const LogSeverity LOG_INFO = 0;
const LogSeverity LOG_WARNING = 1;
const LogSeverity LOG_ERROR = 2;
const LogSeverity LOG_FATAL = 3;
const LogSeverity LOG_NUM_SEVERITIES = 4;

Log usage ：

1）LOG macro : 
LOG It's like c++ The output of the standard library is overloaded <<, It has several common grades , 
image ”VERBOSE“,“INFO”, “WARNING”, “ERROR”, “FATAL”,”NUM_SEVERITIES“ etc.  

such as ”FATAL”LOG Will trigger a breakpoint , And print out the stack backtracking information .

LOG(INFO) << "info Grade     = " << logging::LOG_INFO;
LOG(WARNING) << "WARNING Grade  = " << logging::LOG_WARNING;
LOG(ERROR) << "ERROR Grade    = " << logging::LOG_ERROR;
LOG(FATAL) << "FATAL Grade    = " << logging::LOG_FATAL;

2）LOG_IF macro :

Use LOG_IF Macros can output only when the expression condition is true log：

int if_int = 5;
LOG_IF(INFO, if_int < 10 ) << "if_int < 10";

3）CHECK macro :

CHECK The macro executes when the expression is false LOG(FATAL) The effect of , 

If there is no debugger attached , It will also generate a crash dump.

//CHECK macro , If the condition fails, an LOG(FATAL)
CHECK(0);

4）DLOG macro ： 

DLOG Follow LOG similar , The difference is DLOG Only in DEBUG Mode , 

In Africa DEBUG In mode , This part of the code will not be compiled into the program .

DLOG(INFO) << "DLOG onlg debug";
DLOG_IF(INFO, if_int < 10) << "DLOG_IF onlg debug";
LOG_ASSERT(0);
DLOG_ASSERT(0);

3）VLOG macro ： 

This is an output that can be dynamically adjusted through command line parameters log Macro of policy , These are all INFO Grade .

VLOG(1) << "I'm printed when you run the program with --v=1 or more";
VLOG(2) << "I'm printed when you run the program with --v=2 or more";

4）PLOG macro : 
PLOG In addition to outputting the output information we specify , The last error message of the system is attached , 
windows On is GetLastError(),POSIX On is errno Value .

LOG Macro decomposition ：

#define LOG(severity) LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity))
#define LOG_IS_ON(severity)             ((::logging::LOG_ ## severity) >= ::logging::GetMinLogLevel())
#define LOG_STREAM(severity)             (COMPACT_GOOGLE_LOG_ ## severity.stream())
#define LAZY_STREAM(stream, condition)   !(condition) ? (void) 0 : ::logging::LogMessageVoidify() & (stream)

(logging::LOG_INFO < logging::GetMinLogLevel()) ? (void) 0 : logging::LogMessageVoidify() & (logging::LogMessage(__FILE__, __LINE__, LOG_INFO).stream())

LOG(INFO) << "info Grade " Decompose into
(logging::LOG_INFO < logging::GetMinLogLevel()) ? (void) 0 : logging::LogMessageVoidify() & (logging::LogMessage(__FILE__, __LINE__, LOG_INFO).stream()) << "info Grade "