bdlt_defaulttimetablecache.h

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/// @file bdlt_defaulttimetablecache.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bdlt_defaulttimetablecache.h                                       -*-C++-*-
#ifndef INCLUDED_BDLT_DEFAULTTIMETABLECACHE
#define INCLUDED_BDLT_DEFAULTTIMETABLECACHE
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bdlt_defaulttimetablecache bdlt_defaulttimetablecache
/// @brief  Provide a process-wide default `bdlt::TimetableCache` object.
/// @addtogroup bdl
/// @{
/// @addtogroup bdlt
/// @{
/// @addtogroup bdlt_defaulttimetablecache
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bdlt_defaulttimetablecache-purpose"> Purpose</a>
/// * <a href="#bdlt_defaulttimetablecache-classes"> Classes </a>
/// * <a href="#bdlt_defaulttimetablecache-description"> Description </a>
///   * <a href="#bdlt_defaulttimetablecache-thread-safety"> Thread Safety </a>
///   * <a href="#bdlt_defaulttimetablecache-usage"> Usage </a>
///     * <a href="#bdlt_defaulttimetablecache-example-1-using-bdlt-defaulttimetablecache"> Example 1: Using bdlt::DefaultTimetableCache </a>
///
/// # Purpose {#bdlt_defaulttimetablecache-purpose}
/// Provide a process-wide default `bdlt::TimetableCache` object.
///
/// # Classes {#bdlt_defaulttimetablecache-classes}
///
/// -  bdlt::DefaultTimetableCache: namespace managing a default timetable cache
///
/// @see  bdlt_timetablecache, bdlt_timetableloader
///
/// # Description {#bdlt_defaulttimetablecache-description}
/// This component provides a namespace,
/// `bdlt::DefaultTimetableCache`, for utility functions that initialize,
/// provide access to, and ultimately destroy, a default `bdlt::TimetableCache`
/// object.  The default cache is initialized by calling the (overloaded)
/// `initialize` class method to which a concrete timetable loader and memory
/// allocator must be supplied.  The cache is destroyed by the `destroy` class
/// method.  Note that the timetable-naming convention in effect for the default
/// cache is determined by the loader supplied to `initialize`.
///
/// A timeout may be established for the default cache by supplying an optional
/// `bsls::TimeInterval` value to `initialize`.  When a timeout is in effect for
/// the default cache, a request for a timetable from the cache may incur the
/// reloading of the timetable if the one in the cache has expired (i.e., the
/// time interval defined by the timeout value has elapsed since the timetable
/// was last loaded into the cache).  Timetables will not expire in this fashion
/// if the default cache is not provided with a timeout at initialization.
///
/// Although the cache may be initialized and destroyed multiple times during
/// the lifetime of a process, the expected usage is that the cache would be
/// initialized *once*, typically in `main` before other threads have been
/// created, and destroyed just prior to program termination.  Regardless, the
/// lifetimes of the timetable loader and memory allocator supplied to
/// `initialize` must extend beyond the following (matching) call to `destroy`.
/// While the default timetable cache is in the initialized state, the
/// `instance` method returns an address providing modifiable access to the
/// cache.  Otherwise, `instance` returns 0.
///
/// **WARNING**: Clients should be aware that the address returned by `instance`
/// becomes invalid by a subsequent call to `destroy`.
///
/// ## Thread Safety {#bdlt_defaulttimetablecache-thread-safety}
///
///
/// The `bdlt::DefaultTimetableCache` class is fully thread-safe (see
/// @ref bsldoc_glossary ) provided that the allocator supplied to `initialize` and
/// the default allocator in effect during the lifetime of the default cache are
/// both fully thread-safe.
///
/// ## Usage {#bdlt_defaulttimetablecache-usage}
///
///
/// The following example illustrates how to use `bdlt::DefaultTimetableCache`.
///
/// ### Example 1: Using bdlt::DefaultTimetableCache {#bdlt_defaulttimetablecache-example-1-using-bdlt-defaulttimetablecache}
///
///
/// `bdlt::DefaultTimetableCache` has a particularly simple interface.  This
/// example shows how to use each of its three methods.
///
/// In this example, we assume a hypothetical timetable loader,
/// `MyTimetableLoader`, the details of which are not important other than that
/// it supports timetables identified by "ZERO", "ONE", and "TWO".  Furthermore,
/// the value of the initial transition code for each of these timetables is
/// given by the timetable's name (e.g., if `Z` has the value of the timetable
/// identified as "ZERO", then `0 == Z.initialTransitionCode()`).
///
/// First, we create a timetable loader, an instance of `MyTimetableLoader`, and
/// use it, in turn, to initialize the default timetable cache.  A memory
/// allocator must also be explicitly supplied to the `initialize` method.  The
/// global allocator is suitable in this case (see @ref bslma_default ):
/// @code
/// static MyTimetableLoader loader;
///
/// int rc = bdlt::DefaultTimetableCache::initialize(
///                                         &loader,
///                                         bslma::Default::globalAllocator());
/// assert(!rc);
/// @endcode
/// Note that declaring `loader` to be `static` ensures that it remains valid
/// until the cache is destroyed.  Also note that initialization of the cache
/// would typically be done in `main` before other threads have been created.
///
/// Next, we obtain the address of the default timetable cache using the
/// `instance` class method:
/// @code
/// bdlt::TimetableCache *cachePtr = bdlt::DefaultTimetableCache::instance();
/// assert(cachePtr);
/// @endcode
/// Then, we retrieve the timetable identified by "TWO" from the default cache
/// and verify that 2 is the value of the initial transition code:
/// @code
/// bsl::shared_ptr<const bdlt::Timetable> two = cachePtr->getTimetable("TWO");
/// assert(2 == two->initialTransitionCode());
/// @endcode
/// Next, we fetch the timetable identified by "ONE", this time verifying that 1
/// is the value of the initial transition code for the "ONE" timetable:
/// @code
/// bsl::shared_ptr<const bdlt::Timetable> one = cachePtr->getTimetable("ONE");
/// assert(1 == one->initialTransitionCode());
/// @endcode
/// Finally, we destroy the default timetable cache:
/// @code
/// bdlt::DefaultTimetableCache::destroy();
/// assert(!bdlt::DefaultTimetableCache::instance());
/// @endcode
/// Note that destruction of the default cache would typically be done in `main`
/// just prior to program termination.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bdl
 * @{
 */
/** @addtogroup bdlt
 * @{
 */
/** @addtogroup bdlt_defaulttimetablecache
 * @{
 */
 
#include <bdlscm_version.h>
 
#include <bsls_timeinterval.h>
 
#include <bslma_allocator.h>
 
 
namespace bdlt {
 
class TimetableCache;
class TimetableLoader;
 
                       // ===========================
                       // class DefaultTimetableCache
                       // ===========================
 
/// This `struct` provides a namespace for functions that manage the
/// lifetime of, and access to, a process-wide default
/// `bdlt::TimetableCache` object.  The default cache is initialized by an
/// explicit call to the `initialize` class method, and destroyed by the
/// `destroy` class method.  The default cache may be initialized and
/// destroyed multiple times during the lifetime of a process.  The
/// lifetimes of the timetable loader and memory allocator supplied to
/// `initialize` must extend beyond the following (matching) call to
/// `destroy`.
///
/// All methods of this `struct` are fully thread-safe (see
/// @ref bsldoc_glossary ).
///
/// See @ref bdlt_defaulttimetablecache 
struct DefaultTimetableCache {
 
    // CLASS METHODS
 
    /// Destroy the default `TimetableCache` object managed by this class.
    /// If the default cache is not in the initialized state, this method has no effect.  
    /// 
    /// \note Note that   all addresses returned by earlier calls to
    /// `instance` are invalidated by this method.
    static void destroy();
 
    /// Initialize the default `TimetableCache` object managed by this class
    /// to use the specified `loader` to obtain timetables, to have no
    /// timeout, and to use the specified `allocator` to supply memory.  If
    /// the default cache is already in the initialized state, this method
    /// has no effect.  Return 0 on success, and a non-zero value otherwise. 
    /// 
    /// \pre The behavior is undefined   unless `loader` and `allocator` remain
    /// valid until a subsequent call to `destroy`.
    static int initialize(TimetableLoader  *loader,
                          bslma::Allocator *allocator);
 
    /// Initialize the default `TimetableCache` object managed by this class
    /// to use the specified `loader` to obtain timetables, to have the
    /// specified `timeout`, and to use the specified `allocator` to supply
    /// memory.  If the default cache is already in the initialized state,
    /// this method has no effect.  Return 0 on success, and a non-zero value otherwise.  
    /// 
    /// \pre The behavior is undefined   unless `loader` and
    /// `allocator` remain valid until a subsequent call to `destroy`, and
    /// `bsls::TimeInterval() <= timeout <= bsls::TimeInterval(INT_MAX, 0)`. 
    /// 
    /// \note Note that   a `timeout` value of 0 indicates that a timetable will be
    /// loaded into the default cache by *each* (successful) call to
    /// `TimetableCache::getTimetable` on the cache returned by `instance`.
    static int initialize(TimetableLoader           *loader,
                          const bsls::TimeInterval&  timeout,
                          bslma::Allocator          *allocator);
 
    /// Return an address providing modifiable access to the default
    /// `TimetableCache` object managed by this class, if the default cache
    /// is in the initialized state, and 0 otherwise.  The cache obtains
    /// timetables using the loader that was supplied to the `initialize` method.  
    /// 
    /// \note Note that   the returned address is invalidated by a
    /// subsequent call to `destroy`.
    static TimetableCache *instance();
};
 
// ============================================================================
//                             INLINE DEFINITIONS
// ============================================================================
 
}  // close package namespace
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2018 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */