ball_streamobserver.h

Go to the documentation of this file.

/// @file ball_streamobserver.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// ball_streamobserver.h                                              -*-C++-*-
#ifndef INCLUDED_BALL_STREAMOBSERVER
#define INCLUDED_BALL_STREAMOBSERVER
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup ball_streamobserver ball_streamobserver
/// @brief  Provide an observer that emits log records to a stream.
/// @addtogroup bal
/// @{
/// @addtogroup ball
/// @{
/// @addtogroup ball_streamobserver
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#ball_streamobserver-purpose"> Purpose</a>
/// * <a href="#ball_streamobserver-classes"> Classes </a>
/// * <a href="#ball_streamobserver-description"> Description </a>
///   * <a href="#ball_streamobserver-log-record-formatting"> Log Record Formatting </a>
///   * <a href="#ball_streamobserver-thread-safety"> Thread Safety </a>
///   * <a href="#ball_streamobserver-usage"> Usage </a>
///     * <a href="#ball_streamobserver-example-1-basic-usage"> Example 1: Basic Usage </a>
///
/// # Purpose {#ball_streamobserver-purpose}
/// Provide an observer that emits log records to a stream.
///
/// # Classes {#ball_streamobserver-classes}
///
/// -  ball::StreamObserver: observer that emits log records to a stream
///
/// @see  ball_record, ball_context, ball_loggermanager
///
/// # Description {#ball_streamobserver-description}
/// This component provides a concrete implementation of the
/// `ball::Observer` protocol for receiving and processing log records:
/// @code
///                ,--------------------.
///               ( ball::StreamObserver )
///                `--------------------'
///                          |              ctor
///                          |              setRecordFormatFunctor
///                          V
///                   ,--------------.
///                  ( ball::Observer )
///                   `--------------'
///                                         publish
///                                         releaseRecords
///                                         dtor
/// @endcode
/// `ball::StreamObserver` is a concrete class derived from `ball::Observer`
/// that processes the log records it receives through its `publish` method by
/// writing them to an output stream.  Given its minimal functionality,
/// `ball::StreamObserver` should be used with care in a production environment.
/// It is not recommended to construct this observer with file-based streams due
/// to lack of any file rotation functionality.
///
/// ## Log Record Formatting {#ball_streamobserver-log-record-formatting}
///
///
/// By default, the output format of published log records is:
/// @code
/// DATE_TIME PID THREAD-ID SEVERITY FILE LINE CATEGORY MESSAGE USER-FIELDS
/// @endcode
/// where `DATE` and `TIME` are of the form `DDMonYYYY` and `HH:MM:SS.mmm`,
/// respectively (`Mon` being the 3-letter abbreviation for the month).  For
/// example, assuming that no user-defined fields are present, a log record
/// will have the following appearance when the default format is in effect:
/// @code
/// 18MAY2005_18:58:12.076 7959 1 WARN ball_streamobserver2.t.cpp 404 TEST hi!
/// @endcode
/// The default format can be overridden by supplying a suitable formatting
/// functor to `setRecordFormatFunctor`.  For example, an instance of
/// `ball::RecordStringFormatter` conveniently provides such a functor:
/// @code
/// streamObserver.setRecordFormatFunctor(
///             ball::RecordStringFormatter("\n%I %p:%t %s %f:%l %c %m %u\n"));
/// @endcode
/// The above statement will cause subsequent records to be logged in a format
/// that is almost identical to the default format except that the timestamp
/// attribute will be written in ISO 8601 format.  See
/// @ref ball_recordstringformatter  for information on how format specifications
/// are defined and interpreted.
///
/// Note that the observer emits newline characters at the beginning and at the
/// end of a log record by default, so the user needs to add them explicitly to
/// the format string to preserve this behavior.
///
/// Also note that in the sample message above the timestamp has millisecond
/// precision (`18MAY2005_18:58:12.076`).  If microsecond precision is desired
/// instead, consider using either the `%D` or `%O` format specification
/// supported by @ref ball_recordstringformatter .
///
/// ## Thread Safety {#ball_streamobserver-thread-safety}
///
///
/// All methods of `ball::StreamObserver` are thread-safe, and can be called
/// concurrently by multiple threads.
///
/// ## Usage {#ball_streamobserver-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Basic Usage {#ball_streamobserver-example-1-basic-usage}
///
///
/// The following snippets of code illustrate the basic usage of
/// `ball::StreamObserver`.
///
/// First create a `ball::Record` object `record` and a `ball::Context` object
/// `context`.  Note that the default values for these objects (or their
/// contained objects) are perfectly suitable for logging purposes.
/// @code
/// ball::RecordAttributes attributes;
/// ball::UserFields       fieldValues;
/// ball::Context          context;
///
/// bslma::Allocator *ga = bslma::Default::globalAllocator(0);
/// const bsl::shared_ptr<const ball::Record>
///            record(new (*ga) ball::Record(attributes, fieldValues, ga), ga);
/// @endcode
/// Next, create a stream observer `observer` with the `bsl::cout` as the output
/// stream.
/// @code
/// ball::StreamObserver observer(&bsl::cout);
/// @endcode
/// Finally, publish `record` and `context` to `observer`.
/// @code
/// observer.publish(record, context);
/// @endcode
/// This will produce the following output on `stdout`:
/// @code
/// 01JAN0001_24:00:00.000 0 0 OFF  0
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bal
 * @{
 */
/** @addtogroup ball
 * @{
 */
/** @addtogroup ball_streamobserver
 * @{
 */
 
#include <balscm_version.h>
 
#include <ball_observer.h>
 
#include <bslma_allocator.h>
#include <bslma_bslallocator.h>
#include <bslma_usesbslmaallocator.h>
 
#include <bslmf_nestedtraitdeclaration.h>
 
#include <bslmt_mutex.h>
 
#include <bsls_assert.h>
#include <bsls_keyword.h>
#include <bsls_review.h>
 
#include <bsl_iosfwd.h>
#include <bsl_functional.h>
 
 
namespace ball {
 
class Context;
class Record;
 
                           // ====================
                           // class StreamObserver
                           // ====================
 
/// This class provides a concrete implementation of the `Observer`
/// protocol.  The `publish` method of this class outputs the log records
/// that it receives to an instance of `bsl::ostream` supplied at
/// construction.
///
/// See @ref ball_streamobserver 
class StreamObserver : public Observer {
 
  public:
    // TYPES
 
    /// `RecordFormatFunctor` is an alias for the type of the functor used
    /// for formatting log records to a stream.
    typedef bsl::function<void(bsl::ostream&, const Record&)>
                                                           RecordFormatFunctor;
 
    typedef bsl::allocator<char> allocator_type;
 
  private:
    // DATA
    bsl::ostream        *d_stream_p;   // output sink for log records
 
    bslmt::Mutex         d_mutex;      // serializes concurrent calls to
                                       // 'publish'
 
    RecordFormatFunctor  d_formatter;  // formatting functor used when writing
                                       // to log file
 
    // NOT IMPLEMENTED
    StreamObserver(const StreamObserver&);
    StreamObserver& operator=(const StreamObserver&);
 
    // CLASS METHODS
 
    /// Write the specified log `record` to the specified output `stream`
    /// using the default record format of this stream observer.
    static
    void logRecordDefault(bsl::ostream& stream, const Record& record);
 
  public:
    // TRAITS
    BSLMF_NESTED_TRAIT_DECLARATION(StreamObserver, bslma::UsesBslmaAllocator);
 
    // CREATORS
 
    /// Create a stream observer that transmits log records to the specified
    /// `stream`.  Optionally specify an `allocator` (e.g., the address of a
    /// `bslma::Allocator` object) to supply memory; otherwise, the default
    /// allocator is used.  Note that a default record format is in effect
    /// for stream logging (see `setLogFileFunctor`).
    explicit
    StreamObserver(bsl::ostream          *stream,
                   const allocator_type&  allocator = allocator_type());
 
    /// Destroy this stream observer.
    ~StreamObserver() BSLS_KEYWORD_OVERRIDE;
 
    // MANIPULATORS
    using Observer::publish;
 
    /// Process the specified log `record` having the specified publishing
    /// `context`.  Print `record` and `context` to the `bsl::ostream`
    /// supplied at construction.  The behavior is undefined if `record` or
    /// `context` is modified during the execution of this method.
    void publish(const bsl::shared_ptr<const Record>& record,
                 const Context&                       context)
                                                         BSLS_KEYWORD_OVERRIDE;
 
    /// Discard any shared reference to a `Record` object that was supplied
    /// to the `publish` method, and is held by this observer.  Note that
    /// this operation should be called if resources underlying the
    /// previously provided shared-pointers must be released.
    void releaseRecords() BSLS_KEYWORD_OVERRIDE;
 
    /// Set the formatting functor used when writing records to the log file
    /// of this file observer to the specified `formatter` functor.  Note
    /// that a default format ("\n%d %p %t %s %f %l %c %m %u\n") is in
    /// effect until this method is called (see
    /// @ref ball_recordstringformatter ).  Also note that the observer emits
    /// newline characters at the beginning and at the end of a log record
    /// by default, so the user needs to add them explicitly to the format
    /// string to preserve this behavior.
    void setRecordFormatFunctor(const RecordFormatFunctor& formatter);
};
 
// ============================================================================
//                              INLINE DEFINITIONS
// ============================================================================
 
                           // --------------------
                           // class StreamObserver
                           // --------------------
 
// MANIPULATORS
inline
void StreamObserver::releaseRecords()
{
}
 
}  // close package namespace
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2017 Bloomberg Finance L.P.
//
// 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.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */