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245 lines
8.1 KiB
245 lines
8.1 KiB
#pragma once
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#pragma once
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#ifdef __cplusplus
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#include <cstdint>
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#include <cstddef>
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#include <iterator>
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#else
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#include <stdint.h>
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#include <stddef.h>
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#endif
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#ifdef __cplusplus
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struct sl_log_transaction;
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struct sl_log_transaction_internals;
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namespace sl {
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using cstyle_log_transaction = sl_log_transaction;
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using cstyle_log_transaction_internals = sl_log_transaction_internals;
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/**
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* @brief This class represents a logging transaction
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* @details
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* This class has the following guarantees:
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* - Can be built on the stack safely
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* - This class never allocates using the system allocator
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* - This class does not perform any system call
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* - Finalization cannot happen twice from the public interface
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* - This class may pad the log by up to <tt>std::hardware_destructive_interference</tt> bytes
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* - This class is both thread-safe and multiprocessing-safe to finalize
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*
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* @details
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* This class expects the finalization to occur in the same thread that wrote any data to the log.
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* @pre
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* This class expects the logging buffer to be at least 2 binary orders of magnitude bigger than the largest log
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* message. It is recommended that it is at least 6 binary orders of magnitude bigger than the largest log.
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* @post
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* This class leaves the log in a valid state in accordance to the defined log strategies.
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*/
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class log_transaction {
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char* local_start;
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size_t local_size;
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char* buffer_start;
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size_t buffer_size;
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void* buffer_initiator_page;
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bool is_finalized = false;
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void finalize_impl();
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/**
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* @brief A forward iterator to the current log transaction.
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*/
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class iterator {
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using iterator_category = std::forward_iterator_tag;
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using difference_type = std::ptrdiff_t;
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using value_type = char;
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using pointer = char*;
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using reference = char&;
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log_transaction& owner_ref;
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size_t index;
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public:
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explicit iterator(log_transaction& parent, size_t position = 0)
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: owner_ref(parent)
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, index(((parent.buffer_start - parent.local_start) + position)%parent.buffer_size)
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{}
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iterator& operator++() {
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index+=1;
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index%=owner_ref.buffer_size;
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return *this;
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}
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iterator operator++(int) {
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auto cpy = *this;
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index+=1;
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index%=owner_ref.buffer_size;
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return cpy;
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}
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difference_type operator-(iterator other) const {
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size_t forward, backward;
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forward = owner_ref.buffer_size - index;
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forward += other.index;
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backward = other.index - index;
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return static_cast<difference_type>(std::min(forward, backward));
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}
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reference operator*() {
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return owner_ref.buffer_start[index];
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}
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};
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public:
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/**
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* @brief Starts a transaction. You have to then write your logs between the start and the end of the
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* transaction, then finalize it.
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* @details
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* Guarantees are as follow:
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* - This constructor never allocates using the system allocator
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* - This constructor does not perform any system call
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* - This constructor may pad the log by up to <tt>std::hardware_destructive_interference</tt> bytes
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* - This constructor is both thread-safe and multiprocessing-safe
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*
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* @pre
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* We expect the provided <tt>internal_id</tt> to be valid and registered, if it is not, the transaction may look for a
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* log named "UNHANDLED_ERRORS" and log there instead silently.
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* @post
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* A started transaction MUST be finalized. The log can, upon initiation of the transaction, no longer be
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* pushed to its sink past the current sequence point of the transaction.
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*
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* @post
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* This class will finalize an un-finalized transaction
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* @param internal_id the logger id where the transaction is to happen
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* @param log_size the amount of bytes to write in the transaction.
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*/
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explicit log_transaction(int internal_id, size_t log_size);
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log_transaction(const log_transaction&) = delete;
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log_transaction(log_transaction&&) = delete;
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void operator=(const log_transaction&) = delete;
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void operator=(log_transaction&&) = delete;
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/**
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* @brief Unsafely accesses the underlying buffer
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* @param index The index to the buffer to access
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* @return a reference to an underlying <tt>char</tt>, undefined behaviour is the index is invalid
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*/
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char& operator[](size_t index) {
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return buffer_start[((buffer_start - local_start) + index)%buffer_size];
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}
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/**
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* @brief Obtains a forward iterator to the start of the writable range
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* @return a non-descript iterator to the beginning of the range
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*/
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iterator begin() {
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return iterator(*this, 0);
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}
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/**
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* @brief Obtains a forward iterator to the end of the writable range
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* @return a non-descript iterator to one-past-the-end of the range
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*/
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iterator end() {
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return iterator(*this, local_size);
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}
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/**
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* @brief Finalizes the transaction
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* @details
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* Finalizes a transaction, makes access to the finalized buffer undefined behaviour. If <tt>NDEBUG</tt> is
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* defined, accesses will lead to a near-nullptr dereference.
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*
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* @details
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* You are NOT protected against erroneous double finalization in debug mode. You are protected against double
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* finalization out of debug mode. This protection and these erroneous states do not interact with the
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* destructor, which will finalize transactions if not finalized yet.
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*/
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void finalize();
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/**
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* @see{void finalize()}
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*/
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~log_transaction(){
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if(!is_finalized) finalize_impl();
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}
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};
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}
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#else
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typedef struct sl_log_transaction log_transaction;
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typedef struct sl_log_transaction_internals log_transaction_internals;
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#endif
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/**
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* @brief Represents a transaction in the log. Must be finalized for proper operation of the log.
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*/
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struct sl_log_transaction {
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char* begin; /**< The start of the given writable span */
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char* end; /**< 1 element past the end of the writable span */
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sl_log_transaction_internals* internals; /** Internal, do not touch */
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};
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* @brief Starts a transaction. You have to then write your logs between the start and the end of the transaction,
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* then finalize it.
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* @details
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* Guarantees are as follow:
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* - This function never allocates using the system allocator
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* - This function does not perform any system call
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* - This function may need to pad the log to be operable by C easily
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* - This function is both thread-safe and multiprocessing-safe
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*
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* @pre
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* We expect the provided internal_id to be valid and registered, if it is not, the transaction may look for a log
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* named "UNHANDLED_ERRORS" and log there instead silently.
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* @post
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* A started transaction MUST be finalized. The log can, upon initiation of the transaction, no longer be pushed to
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* its sink past the current sequence point of the transaction.
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* @param internal_id the logger id where the transaction is to happen
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* @param log_size the amount of bytes to write in the transaction.
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* @return a transaction of at least log_size bytes
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*/
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sl_log_transaction sl_start_log_transaction(int internal_id, size_t log_size);
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/**
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* @brief Finalizes a transaction.
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* @details
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* Be cautious. Finalizing a finalized transaction should NEVER be done. It may wait forever, screw up your log, and
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* clog your log queue forever.
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* @pre
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* The transaction to finalize must never have been finalized before. If it has been finalized before, the
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* finalization may never terminate.
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* @post
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* All data written in the transaction is thenceforth scheduled to be written. The transaction state is now moot
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* and should not be accessed further, and should possibly be cleared.
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* @param target the transaction to finalize.
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*/
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void sl_finalize_log_transaction(sl_log_transaction target);
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/**
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* @brief Clears a transaction object. This is not required but may help prevent bugs.
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* @param to_clear
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*/
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inline void sl_clear_transaction(sl_log_transaction* to_clear) {
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#ifdef NDEBUG
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do {} while(false);
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#else
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#ifdef __cplusplus
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to_clear->begin = nullptr;
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to_clear->end = nullptr;
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to_clear->internals = nullptr;
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#else
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to_clear->begin = NULL;
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to_clear->end = NULL;
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to_clear->internals = NULL;
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#endif
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#endif
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}
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#ifdef __cplusplus
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}
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#endif
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