logging: add a small example program

Summary:
This adds a small example program which demonstrates using the logging library.

This gives a very basic example of how the library is intended to be used, and
can also be used to play around with controlling the log levels from the
command line argument.

Reviewed By: wez

Differential Revision: D5083104

fbshipit-source-id: ab09c6c88db33065f6e39f35b28014f2a6153cef

.gitignore

@@ -22,6 +22,7 @@ folly/**/test/*_test_using_jemalloc
 folly/**/test/*.trs
 folly/config.*
 folly/configure
+folly/experimental/logging/example/logging_example
 folly/libfolly.pc
 folly/m4/libtool.m4
 folly/m4/ltoptions.m4

folly/configure.ac

@@ -608,6 +608,7 @@ AC_CONFIG_FILES([Makefile
                  experimental/Makefile
                  experimental/io/test/Makefile
                  experimental/logging/Makefile
+                 experimental/logging/example/Makefile
                  experimental/symbolizer/Makefile
                  init/Makefile
                  stats/test/Makefile])

folly/experimental/logging/Makefile.am

-SUBDIRS = .
+SUBDIRS = . example
 
 lib_LTLIBRARIES = libfollylogging.la
 

folly/experimental/logging/example/Makefile.am

+noinst_PROGRAMS = logging_example
+noinst_LTLIBRARIES = libfollylogging_example.la
+
+logging_example_SOURCES = main.cpp
+logging_example_LDADD = libfollylogging_example.la
+
+libfollylogging_example_la_SOURCES = lib.cpp
+libfollylogging_example_la_LIBADD = \
+	$(top_builddir)/experimental/logging/libfollylogging.la

folly/experimental/logging/example/lib.cpp

+/*
+ * Copyright 2004-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include <folly/experimental/logging/example/lib.h>
+
+namespace example {
+ExampleObject::~ExampleObject() {
+  // All XLOG() statements in this file will log to the category
+  // folly.experimental.logging.example.lib
+  XLOGF(DBG1, "ExampleObject({}) at {} destroyed", value_, this);
+}
+}

folly/experimental/logging/example/lib.h

+/*
+ * Copyright 2004-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <folly/Range.h>
+#include <folly/experimental/logging/xlog.h>
+
+namespace example {
+
+class ExampleObject {
+ public:
+  explicit ExampleObject(folly::StringPiece str) : value_{str.str()} {
+    // All XLOG() statements in this file will log to the category
+    // folly.experimental.logging.example.lib
+    XLOGF(DBG1, "ExampleObject({}) constructed at {}", value_, this);
+  }
+  ~ExampleObject();
+
+  void doStuff();
+
+ private:
+  std::string value_;
+};
+}

folly/experimental/logging/example/main.cpp

+/*
+ * Copyright 2004-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include <folly/experimental/logging/Init.h>
+#include <folly/experimental/logging/xlog.h>
+#include <folly/init/Init.h>
+
+#include <folly/experimental/logging/example/lib.h>
+
+DEFINE_string(logging, "", "Logging category configuration string");
+
+using namespace example;
+using folly::LogLevel;
+
+// Invoking code that uses XLOG() statements before main is safe,
+// but will not log anywhere, since no handlers are configured yet.
+static ExampleObject staticInitialized("static");
+
+int main(int argc, char* argv[]) {
+  // Using log macros before configuring any log levels or log handlers is
+  // safe, but the messages will always be ignore since no handlers are defined.
+  XLOG(INFO, "no handlers configured yet, so this will go nowhere");
+  printf("main starting\n");
+  fflush(stdout);
+
+  // Call folly::init() and then initialize log levels and handlers
+  folly::init(&argc, &argv);
+  initLoggingGlogStyle(FLAGS_logging, LogLevel::INFO);
+
+  // All XLOG() statements in this file will log to the category
+  // folly.experimental.logging.example.main
+  XLOG(INFO, "now log messages will be sent to stderr");
+
+  XLOG(DBG1, "log arguments are concatenated: ", 12345, ", ", 92.0);
+  XLOGF(DBG1, "XLOGF supports {}-style formatting: {:.3f}", "python", 1.0 / 3);
+  XLOG(DBG2) << "streaming syntax is also supported: " << 1234;
+  XLOG(DBG2, "you can even", " mix function-style") << " and streaming "
+                                                    << "syntax";
+
+  ExampleObject("foo");
+  XLOG(INFO, "main returning");
+  return 0;
+}