Life cycle refers to the birth, aging, illness and death of an object.[1]
The concept of life cycle is widely used, especially in many fields such as politics, economy, environment, technology and society. Its basic meaning can be understood as the whole process of "cradle to grave".For a product, it is the whole process of coming from nature to nature, which includes the collection and processing of raw materials required for manufacturing productsProduction process, including product storage, transportation, etcCirculation processIt also includes the use process of products and the process of discarding or disposing products back to nature, which constitutes a complete product life cycle.
Life cycle assessment (LCA) originated in the 1960s. Due to the emergence of the energy crisis and the huge impact on society, the United States and Britain have successively carried out in-depth research on energy utilization, and the concept and idea of LCA has gradually formed.It is worth noting that LCA laterecological environmentThe field has a wide range of applications.
Looking at the history of LCA, its development can be divided into three stages.
In the early 1970s, the research mainly focused onPackaging wasteFor example, the Midwest Re research Institute (MRI)Coca Cola CompanyOf beverage packaging bottlesEvaluation studyThis research attempts to trace and quantitatively study the whole process from raw material mining to final disposal of waste, revealinglife cycle assessment The prologue of.
In the mid-1970s, attention was paid to the research of life cycle assessment. Some scholarsscientific research institutionAnd the government invested a certain amount of manpower and material resources to carry out research work.At this stage, the focus of research is on energy issues and solid waste gas.,Some research and consulting institutions in Europe and the United States, based on relevant ideas, have explored methods for waste management, studied potential impacts such as pollutant emissions and resource consumption, and promoted the development of LCA.
In the 1980s, the "diaper incident" attracted people's attention in a state of the United States.The so-called "diaper incident" is an incident caused by the prohibition and reuse of disposable diapers.Due to the large use of disposable diapers, a large number ofSolid wasteLandfill treatment of these wastes requires a large amount of land, which is under great pressure. Therefore, the Parliament issued a law prohibiting the use of disposable diapers and switching to multiple diapers. Due to the washing of multiple diapers, water resources and detergents are increasedConsumption, which not only aggravates the contradiction between supply and demand of water resources in the state, but also increases the pollution of water resources. The state still prohibits the use of water resources with the idea of life cycledisposable diaperThe re evaluation was carried out, and the evaluation results showed that the use of disposable diapers was more reasonable, and disposable diapers were restored to use.The "diaper incident" islife cycle assessment One of the more typical examples, which has a greater impact.
becauseenvironmental problemsIt not only affects the economic development, but also threatens the survival of human beingsenvironmental consciousness Life cycle assessment has gained unprecedented development opportunities.
In August 1990, the International Society of Environmental Toxicology and Chemistry (SETAC) put forward the concept of "life cycle assessment" for the first time at the international seminar on life cycle assessment, and established LCAAdvisory group, responsible for the research of LCA methodology and application.Since 1990, SETAC has changedcountries and regions More than 20 sessions of LCASeminar, published some important guiding literature, and made great contributions to the development and improvement of LCA methodology and the standardization of its application.At the same time, some European countries have formulated a series of policies and regulations to promote LCA, such as the "Ecological Mark Plan"“ecological management AndAudit regulations”, "Packaging and Packaging Waste Management Guidelines", LCA began to educate, exchangepublic policy、scientific researchandMethodologyResearch and other aspects have been widely applied.For example, Japan has completed LCA for dozens of products.The Original LCA Materials published in 1993 was the most comprehensive overview report of LCA activities at that time.
SPOLD, an industry association, is responsible forlife cycle assessment We have also carried out a series of work, and in recent years, we have been committed to maintaining and developing the SPOLD formatInventory analysisAnd SPOLDData networkuse.United Nations Environment ProgrammeIn the United States in 1998San FranciscoThe seminar on "Towards the Global Use of LCA" was held with the purpose of increasing the use of LCA globally to achieve sustainable development. The conference proposed suggestions on the use of LCA globally and action plans in education, communication, public policy, scientific research and methodological development.
International Organization for StandardizationIn June 1993, TC207, a technical committee in charge of environmental management, was established to formulate life cycle assessment standards.Following the release of the first LCA in 1997international standardAfter ISO14040 Principles and Framework of Life Cycle Assessment, ISO14041 Determination of Purpose and Scope of Life Cycle Assessment, Life Cycle Inventory Analysis, ISO14042 Life Cycle Assessment Life Cycle Impact Assessment, ISO14043 Life Cycle Assessment Life Cycle InterpretationISO/TR14047 Life Cycle Assessment ISO14042 Application Example and ISO/TR14049 Life Cycle Assessment ISO14041 Application Example.
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There are broad sense and narrow sense.In a narrow sense, it refers to the original meaning--life sciencesThe term refers to the whole process of an organism from birth, growth, maturity, decline to death.Broadly defined as the extension and development of the original meaning, it generally refers to the nature andhuman societyvariousobjective thingsThe periodic changes and their laws of.
Product life cycle theoryAmerican economistsRaymond Vernon It was proposed in 1966 in International Investment and Trade in the Product Life Cycle.It starts from the technological change of product production, analyzes the product life cycle and its impact on the trade pattern.He believes that finished products, like biology, have a life cycle, which will successively go through five different stages: innovation, growth, maturity, standardization and decline.
productlife cycle assessment It is an evaluation related to products, processes or actionsEnvironmental loadIt is an objective process to identify and quantify the use of energy and materials and environmental emissions, evaluate the impact of these use of energy and materials and environmental emissions, and evaluate and implement opportunities that affect environmental improvement.The assessment covers the whole life cycle of products, processes or activities, including raw material extraction and processing, production, transportation and distribution, use, reuse and maintenance, recycling and final disposal (internationalEnvironmental ToxicologyAnd the Chemical Society).
Product life cycle assessment is the compilation and assessment of inputs, outputs and potential environmental impacts in the life cycle of a product system（International Organization for Standardization）。
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The above definitions are all around product to environmentImpact assessmentAnd made.This has a lot to do with the widespread application of this idea in the environmental field.From a broader perspective, the definition is still somewhat narrow. In order to make more fields accept this concept, its connotation should be further expanded.
The author defines it as:life cycle assessment It is the evaluation of the whole process of something from its birth to its demise and the effects produced after its demise.
Product/industry life cycle is a very useful method to help enterprises formulate appropriate strategies according to whether the industry is in growth, maturity, recession or other states.
This method assumes that the competitive situation of an enterprise in each stage of its life cycle (development, growth, maturity, recession) is different.For example, development - products/services are purchased by those "early adopters" who are insensitive to price, so their profits will be high. On the other hand, a large amount of investment is required to develop products with better quality and popular prices, which will erode profits.
In this method, since it is assumed that things will inevitably follow a defined life cycle pattern, this method may lead to predictable rather than creative and innovative strategies.
The concept of life cycle is moreconstructiveThe application of isDemand Life Cycle Theory。This theory assumes that customers (individuals, private or public enterprises) have certain specific needs (entertainment, education, transportation, social networking, information exchange, etc.) that they want to be satisfied.At different times, there will be different products to meet these needs.
The technology is constantly developing, and the populationStatistical characteristicsOver time,Political environmentAnd vacillated between different power groups,Consumer preferencesIt will also change.Rather than fighting to protect a specific product, it is better to ensure that you can continue to meetCustomer needsAnd fight.
Many TV manufacturers see that they are in a mature TV market, but they do not see that they are still in a growing family entertainment market.So they gave up the market and watched helplesslyvideo recorder, home computers and future HDTV（HDTV）They have entered the explosive growth together.
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International Organization for StandardizationISO established Technical Committee TC207 in charge of environmental management in June 1993, responsible for formulatinglife cycle assessment Standards.Following the release of the first LCA in 1997international standardAfter ISO14040 Environmental Management Life Cycle Assessment Principles and Framework, ISO14041 Determination and List Analysis of Environmental Management Life Cycle Assessment Objectives and Specifications, ISO14042 Environmental Management Life Cycle Impact Assessment, ISO14043 Life Cycle Interpretation in Life Cycle AssessmentISO/TR14047 Application Examples of ISO14042 and ISO/TR14049 Application Examples of ISO14041.
entomologydefinition:insectOf eggs (orlarvaandnymph）From leaving the parent toadultSexual maturityUntil the generation of offspringOntogenyProcess, called life cycle（lifecycle）Or one generation, the time required to complete a generation is called generation duration.
In most cases, each Android application will run on its ownLinuxIn process.When some code of the application needs to be executed, the process will be created and will remain running until the process is no longer needed and the system needs to release the memory it occupies for other applications.
AndroidAn important and special feature is that the life cycle of an application process is not determined byapplication programoneselfdirect controlIt is determined by the system according to some characteristics of running applications, including the importance of these applications to users and all available memory of the system.
It is very important for application developers to understand the impact of different application components (especially Activity, Service and Intent Receiver) on the life cycle of application processes.If these components are not used correctly, the process will be destroyed by the system when the application is processing important work.
A common error in the process life cycle is that when an Intent Receiver receives an Intent in its onReceiveIntent() method, it will return from this method.Once returned from this method, the system will consider that the Intent Receiver is no longer active, and will also consider itsHost ProcessNo need (unless there are other application components in the host process).Thus, the system will destroy the process at any time, reclaim memory, and terminate the running child threads.The solution to the problem is to start a service in the Intent Receiver, so that the system will know that there is still active work in the process.
In order to decideinsufficient memoryIn case of which process to destroy, Android will divide these processes into an "importance hierarchy" according to the components running in these processes and the status of these components (as shown in Figure 1).
Figure 1 Android Application Process Hierarchy
1. The foreground process has an activity (its onResume() method has been called), or it may be a process with running Intent Receiver (its onReceiveIntent() method is running).In the system, there are few such processes. These processes will be destroyed only when the memory is too low to support the continuous operation of these processes. Usually, the device has reached the required levelMemory sortingIn order to guaranteeuser interfaceIf you do not stop responding, you can only destroy these processes;
2. A visible process is an activity process (whose onPause() has been called) that is visible on the screen but not displayed in the foreground.For example, a foreground activity displayed as a dialog box is displayed on the screen, while the next level of activity behind it is still visible.Such processes are very important and will not be destroyed in general. They will be destroyed only to ensure the normal operation of all foreground processes.AndroidGenerally, there are a few visible processes in the process. Only under special circumstances will the Android system clear the visible processes to ensure the resources of the foreground process.
3. A service process is a process that has a service started by the startService () method.Although these processes are invisible to users, they usually do things that users care about (such as the backgroundmusic player Playing music or uploading and downloading data in the backgroundnetwork service）。Therefore, the system will only destroy the foreground process and the visible process in order to ensure their normal operation.
4、Background processIt has an Activity (onStop() method has been called) process that is invisible to the user.These processes do not directly affect the user experience.If these processes have completed their own life cycle correctly, the system will destroy these processes at any time toFree memory。There are usually many such processes running, so these processes will be saved in aLRUList toGuaranteed onWhen the memory is insufficient, the last process the user sees will be destroyed at the end.
5. Empty processes are processes that do not have any active application components.The reason for keeping these processes is that, as a cache, the next time the application component to which they belong needs to be started, the startup time will be shortened.Similarly, in order to balance these cached empty processes with the underlying core cachesystem resource, the system will often destroy these empty processes.
When a process is to be classified, the system will select the most important component of all activities in the process as the basis.
An activity is usually a separate screen, and the activity life cycle refers to the process of an activity from startup to destruction.Activities in the system are managed by an activity stack.When a new activity is started, it will be placed in theTop of stack, becomes a running activity, and the previous activity is kept in the stack and will not be placed in the foreground until the running activity exits.
Activity has four states:
1. Active or Running: also known asrunning state , at the top of the activity stack, at the top of the user interface, can be seen by users and interact with users;
2. Paused: The activity loses focus, and the activity interface is partially blocked. The activity is no longer at the top of the user interface, and cannot interact with users.A suspended activity remains active (all statuses, member information, andWindow ManagerRemain connected), but in thesystem memoryIf it is not enough, it will be killed;
3. Stopped: The activity cannot be seen by the user on the interface at all, that is, the activity is completely obscured by other activities, but it still keeps all the status and member information, except that it is no longer visible and its window is hidden;
4. Inactive state (Killed): When the system memory needs to be used elsewhere, an activity in the stopped state is killed.
If an activity is in Paused or Stopped status, it can be restored or deleted.If a deleted (killed) activity needs to be restored, it needs to be restarted.
Figure 2 Activity Life Cycle
Figure 2 shows the importance of activitystate transition The rectangular box indicates the callback interface between the status transitions of the activity, and the colored oval indicates the status of the activity.In Figure 2, Activity has three key loops:
The whole life cycle starts from onCreate() to onDestroy().Activity sets all "global" states in onCreate() and releases all resources in onDestory().For example, if an activity has a thread running in the background to download data from the network, the activity can create a thread in onCreate() and stop the thread in onDestory().
Visible life cycle, from onStart() to onStop().During this time, you can see that the activity is on the screen, although it may not be in the foreground and cannot interact with users.Between these two interfaces, you need to keep theUIData and resources. For example, you can register an Intent Receiver in onStart to listen to changes in the UI caused by data changes. When the display is no longer needed, you can log it off in onStop().OnStart() and onStop() can be called multiple times, because Activity can switch between visible and hidden at any time.
The lifecycle of the foreground starts with onResume() and ends with onPause().During this period, this activity is at the top of all activities and interacts with users.Activity can often switch between the resumed and paid states. For example, when the device is ready to sleep, when an activity processing result is distributed, and when a new Intent is distributed.
The entire life cycle of an activity is defined in the following interface methods, and all methods can be overloaded.All activities need to implement onCreate() to initialize settings. Most activities need to implement onPause() to submit changed data. Currently, most activities also need to implement onFreeze() interface to restore the state set in onCreate().
