balb_reservationguard.h

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/// @file balb_reservationguard.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// balb_reservationguard.h                                            -*-C++-*-
#ifndef INCLUDED_BALB_RESERVATIONGUARD
#define INCLUDED_BALB_RESERVATIONGUARD
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup balb_reservationguard balb_reservationguard
/// @brief  Provide a generic proctor for rate controlling objects.
/// @addtogroup bal
/// @{
/// @addtogroup balb
/// @{
/// @addtogroup balb_reservationguard
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#balb_reservationguard-purpose"> Purpose</a>
/// * <a href="#balb_reservationguard-classes"> Classes </a>
/// * <a href="#balb_reservationguard-description"> Description </a>
///   * <a href="#balb_reservationguard-usage"> Usage </a>
///     * <a href="#balb_reservationguard-example-1-guarding-units-reservation-in-operations-with-balb-leakybucket"> Example 1: Guarding units reservation in operations with balb::LeakyBucket </a>
///
/// # Purpose {#balb_reservationguard-purpose}
/// Provide a generic proctor for rate controlling objects.
///
/// # Classes {#balb_reservationguard-classes}
///
/// -  balb::ReservationGuard: a guard for reserving resources from rate limiters.
///
/// @see  balb_leakybucket, balb_ratelimiter
///
/// # Description {#balb_reservationguard-description}
/// This component provides generic proctor to automatically
/// reserve and release units from a rate controlling object.  The rate
/// controlling object can be of any type (typically either a
/// `balb::RateLimiter` or `balb::LeakyBucket`) that provides the following
/// methods:
/// @code
/// void reserve(bsls::Types::Uint64 numOfUnits);
/// void submitReserved(bsls::Types::Uint64 numOfUnits);
/// void cancelReserved(bsls::Types::Uint64 numOfUnits);
/// @endcode
/// Use `balb::ReservationGuard` to ensure that reserved units will be correctly
/// returned to a rate controlling object in a programming scope.  Note that
/// `balb::ReservationGuard` does not assume ownership of the rate controlling
/// object.
///
/// ## Usage {#balb_reservationguard-usage}
///
///
/// This section illustrates the intended use of this component.
///
/// ### Example 1: Guarding units reservation in operations with balb::LeakyBucket {#balb_reservationguard-example-1-guarding-units-reservation-in-operations-with-balb-leakybucket}
///
///
/// Suppose that we are limiting the rate of network traffic generation using a
/// `balb::LeakyBucket` object.  We send data buffer over a network interface
/// using the `mySendData` function:
/// @code
/// /// Send a specified `dataSize` amount of data over the network.  Return the
/// /// amount of data actually sent.  Throw an exception if a network failure
/// /// is detected.
/// bsls::Types::Uint64 mySendData(size_t dataSize);
/// @endcode
/// Notice that the `mySendData` function may throw an exception; therefore, we
/// should wait until `mySendData` returns before indicating the amount of data
/// sent to the leaky bucket.
///
/// Further suppose that multiple threads are sending network data and sharing
/// the same leaky bucket.  If every thread simply checks for overflowing of the
/// leaky bucket, send data, and then submit to the leaky bucket, then the rate
/// of data usage may exceed the limits imposed by the leaky bucket due to race
/// conditions.  We can avoid the this issue by reserving the amount of data
/// immediately after checking whether the leaky bucket has overflown and submit
/// the reserved amount after the data has been sent.  However, this process
/// could lead to the loss of the reserved units (effectively decreasing the
/// leaky bucket's capacity) if `mySendData` throws an exception.
/// `balb::ReservationGuard` is designed to resolve this issue.
///
/// First, we define the size of each data chunk and the total size of the data
/// to send:
/// @code
/// const bsls::Types::Uint64 CHUNK_SIZE = 256;
/// bsls::Types::Uint64       bytesSent  = 0;
/// bsls::Types::Uint64       totalSize  = 10 * 1024; // in bytes
/// @endcode
/// Then, we create a `balb::LeakyBucket` object to limit the rate of data
/// transmission:
/// @code
/// bsls::Types::Uint64 rate     = 512;
/// bsls::Types::Uint64 capacity = 1536;
/// bsls::TimeInterval  now      = bdlt::CurrentTime::now();
/// balb::LeakyBucket   bucket(rate, capacity, now);
/// @endcode
/// Next, we send the chunks of data using a loop.  For each iteration, we check
/// whether submitting another byte would cause the leaky bucket to overflow:
/// @code
/// while (bytesSent < totalSize) {
///
///     now = bdlt::CurrentTime::now();
///     if (!bucket.wouldOverflow(now)) {
/// @endcode
/// Now, if the leaky bucket would not overflow, we create a
/// `balb::ReservationGuard` object to reserve the amount of data to be sent:
/// @code
///         balb::ReservationGuard<balb::LeakyBucket> guard(&bucket,
///                                                         CHUNK_SIZE);
/// @endcode
/// Then, we use the `mySendData` function to send the data chunk over the
/// network.  After the data had been sent, we submit the amount of reserved
/// data that was actually sent:
/// @code
///         bsls::Types::Uint64 result;
///         result = mySendData(CHUNK_SIZE);
///         bytesSent += result;
///         guard.submitReserved(result);
/// @endcode
/// Note that we do not have manually cancel any remaining units reserved by the
/// `balb::ReservationGuard` object either because `mySendData` threw an
/// exception, or the data was only partially sent, because when the guard
/// object goes out of scope, all remaining reserved units will be automatically
/// cancelled.
/// @code
///     }
/// @endcode
/// Finally, if submitting another byte will cause the leaky bucket to overflow,
/// then we wait until the submission will be allowed by waiting for an amount
/// time returned by the `calculateTimeToSubmit` method:
/// @code
///     else {
///         bsls::TimeInterval  timeToSubmit = bucket.calculateTimeToSubmit(
///                                                                       now);
///         bsls::Types::Uint64 uS = timeToSubmit.totalMicroseconds() +
///                                (timeToSubmit.nanoseconds() % 1000) ? 1 : 0;
///         bslmt::ThreadUtil::microSleep(static_cast<int>(uS));
///     }
/// }
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bal
 * @{
 */
/** @addtogroup balb
 * @{
 */
/** @addtogroup balb_reservationguard
 * @{
 */
 
#include <balscm_version.h>
 
#include <bsls_assert.h>
#include <bsls_asserttest.h>
#include <bsls_types.h>
 
 
namespace balb {
 
                           //=======================
                           // class ReservationGuard
                           //=======================
 
/// This class template implements a proctor for reserving and cancelling
/// units in a rate controlling object.
///
/// This class:
/// * is *exception* *neutral* (agnostic)
/// * is *const* *thread-safe*
/// For terminology see @ref bsldoc_glossary .
///
/// See @ref balb_reservationguard 
template<class TYPE>
class ReservationGuard {
 
    // DATA
    TYPE                  *d_rateController_p;  // Pointer to the rate
                                                // controlling object in which
                                                // the units are reserved.
 
    bsls::Types::Uint64     d_unitsReserved;    // Number of units reserved by
                                                // this object.
 
  private:
    // NOT IMPLEMENTED
    ReservationGuard();
    ReservationGuard& operator =(const ReservationGuard<TYPE>&);
    ReservationGuard(const ReservationGuard<TYPE>&);
 
  public:
    // CREATORS
 
    /// Create a `ReservationGuard` object guarding the specified
    /// `rateController` and reserving the specified `numUnits`.
    ReservationGuard(TYPE* rateController, bsls::Types::Uint64 numUnits);
 
    /// Destroy this object.  Invoke the `cancelReserved` method for the
    /// remaining remaining units reserved by this proctor.
    ~ReservationGuard();
 
    // MANIPULATORS
 
    /// Cancel the specified `numUnits` from the reserve units guarded by
    /// this object.  Subtract the `numUnits` from `unitsReserved` and
    /// invoke the `cancelReserved` method on the guarded object for
    /// `numUnits`.  After this operation, the number of reserved units
    /// guarded by this object will be reduced by `numUnits`.  
    /// 
    /// \pre The behavior is undefined   unless `numUnits <= unitsReserved()`.
    void cancelReserved(bsls::Types::Uint64 numUnits);
 
    /// Submit the specified `numUnits` from the reserve units guarded by
    /// this object.  After this operation, the number of reserved units
    /// guarded by this object will be reduced by `numUnits`.  
    /// 
    /// \pre The behavior is undefined   unless `numUnits <= unitsReserved()`.
    void submitReserved(bsls::Types::Uint64 numUnits);
 
    // ACCESSORS
 
    /// Return a pointer to the rate controlling object used by this object.
    TYPE *ptr() const;
 
    /// Return the number of units reserved by this object.
    bsls::Types::Uint64 unitsReserved() const;
};
 
// ============================================================================
//                      INLINE FUNCTION DEFINITIONS
// ============================================================================
 
                           //-----------------------
                           // class ReservationGuard
                           //-----------------------
 
// CREATORS
template <class TYPE>
inline
ReservationGuard<TYPE>::ReservationGuard(TYPE*               rateController,
                                         bsls::Types::Uint64 numUnits)
{
    BSLS_ASSERT_SAFE(0 != rateController);
 
    d_rateController_p = rateController;
    d_unitsReserved    = numUnits;
 
    d_rateController_p->reserve(numUnits);
}
 
template <class TYPE>
inline
ReservationGuard<TYPE>::~ReservationGuard()
{
    d_rateController_p->cancelReserved(d_unitsReserved);
}
 
// ACCESSORS
template <class TYPE>
inline
TYPE *ReservationGuard<TYPE>::ptr() const
{
    return d_rateController_p;
}
 
template <class TYPE>
inline
bsls::Types::Uint64 ReservationGuard<TYPE>::unitsReserved() const
{
    return d_unitsReserved;
}
 
// MANIPULATORS
template <class TYPE>
inline
void ReservationGuard<TYPE>::cancelReserved(bsls::Types::Uint64 numUnits)
{
    BSLS_ASSERT_SAFE(numUnits <= d_unitsReserved);
 
    d_rateController_p->cancelReserved(numUnits);
    d_unitsReserved -= numUnits;
}
 
template <class TYPE>
inline
void ReservationGuard<TYPE>::submitReserved(bsls::Types::Uint64 numUnits)
{
    BSLS_ASSERT_SAFE(numUnits <= d_unitsReserved);
 
    d_rateController_p->submitReserved(numUnits);
    d_unitsReserved -= numUnits;
}
 
}  // close package namespace
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2021 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */