JAVA17
Conceptual processes for multithreaded processes and threadsL programs that are running
L program is stored in the hard disk when running into memory
L Every program in memory is called a process.
L and each process has a separate function
ThreadL multi-threaded download in thunder
There are many ways to arrange one at a time in the Main method
L For example
Internet cafes in multiple computers
Multiple Road traffic
Threading ConceptsL CPU Central Processor Inter AWD
L Quad Core Eight threads
L 360 anti-virus tools
L Multi-Threaded download
L did not improve the speed of the internet but multithreading increased
Running mode time-sharing scheduling for threadsAll threads use CPU resources in turn to evenly allocate CPU time to a thread
Preemptive schedulingHigh priority multi-use random selection with the same CPU resource priority as one for scheduling
L
Main threadL Compile
L JVM runs the Main method
L Find operating system thread
l have an execution path for the CPU the main path has a name, main.
L This is the main thread.
L multithreading even if one thread is wrong other threads will execute
Thread class overviewL Java.lang in Bag
L JVM allows programs to run multiple threads
• Each thread has a priority
L Create threads with two methods
L define a class to inherit the thread override the Run method
L Instantiate an object of this class in a test class call the Start method
L Start method can only be performed once
l The order of execution is not the same as before
L graphic
L Call the run and start differences
The thread class inherits this class is the thread class
L Create the thread class object directly, the Run method is the method of this class, there is no operation can not run the custom code, so we need to inherit this class to rewrite the Run method and then execute the code we need to execute in another thread
The function of the Run method is to execute the code we want to execute in the new thread
Memory graph of threads runningL Main method advanced into
L then call the Start method Run method ready to be called by the JVM
L Run method does not enter this stack will open a new stack space to execute the Run method separately
L
Get Thread NameL Main main thread name is main
L console Gets the default thread name
L GetName Get thread name
Calling the parent class method can not write super
L Get main thread name
Static Thread CurrentThread ();
Gets the name of the thread that is running this method returns the thread type
Simplified
Set the thread nameL SetName ()
L Construction Method rerouting name
L thread stops at a specific time
L Throw exception
This exception is thrown when awakened during hibernation
Runnable interfaceL Another way to implement threading
L Implement Interface Runnable
L Implementation Method Run
ExampleL Premise inheritance or interface implementation
L New parent class or interface implementation () {overriding abstract method}
l Example
L New State
L RUNNABLE The running state is executing this thread in the JVM virtual machine
L BLOCKED Blocked
Deadlock CPU Resource was robbed
L waitting wait for infinite sleep
Methods in the Object class
L Timed_ waitting Sleep
L treminated Death Status
L blocked resources that have CPU execution eligibility waiting for CPU
L hibernate wait thread abandons CPU's execution qualification
Thread Pool OverviewL is a container that can hold multiple threads
L Create multiple threads to be stored in the collection at the beginning of the program
L Use the Remove method to remove the thread and add it again with add
L've been developing thread pools myself before.
L Jdk1.5 after adding thread pool technology
Using the thread pool mode runable interfaceL created by thread pool factory
L re-call method in thread pool to create thread
L Executors Class
A) Create multiple
b) Create a single
c) The return value is the thread pool class object
The console does not stop when the thread runs out and has returned to the thread pool
Thread Name
Stopping a thread
Shutdown Thread Stop
Implementing Thread Callable MethodsL Runnable interface thread runs out no results can not throw exception
L Jdk1.5 after a callable interface call method is equivalent to run
L Call method has return value can throw exception
L Create thread pool objects first with factory class static method Newfixedrhreadpool
L Thread Object Call method submit thread task passed in a callable interface implementation class
l Example
Parent interface throws an exception subclass to throw an exception or throw an exception
PracticeL Asynchronous computation
Thread operations shared data security issues ticketing exampleMultiple threads running concurrently running a piece of code at the same time
L The result of each run is the same as single-threaded run results
L Ticketing
L multiple ways to purchase tickets multiple threads operate the same data
L should update the data at the same time otherwise there will be security issues
l Example
Data is OK but there are security implications
Security issues raisedL T0 judgment is ready to begin operation
L CPU is preempted by T1 thread at this time
L T1 The judgment is ready to be operated
L was preempted by T2 thread at this time
L T2 The judgment is ready to be operated
L CPU resources get T0 to perform operations at this time – data is 0
L T1 also executes-data is-1
L T2 also executes--data is-2
• Thread safety issues occur
L Simulation Example
Synchronzied (arbitrary object) {
Shared data for thread operations
}
Cannot write anonymous object
It's getting safe.
But it's slowing down.
Principle of executionL Synchronization Object Arbitrary object
L Object: Sync lock Object Monitor
L Synchronous guarantee Security The thread that is not locked cannot execute only wait
L The thread encounters the synchronization code block and then determines if the sync lock has
L if not, wait.
L Set the sync lock to 0 if there is a get lock
L Enter the synchronization code block at this point, if you hibernate
L Another thread came over to execute the code will determine if there is a synchronization lock is obviously not at this time, so I can't get into the code block can not execute code
L Continue executing code and releasing the sync lock if the first thread wakes up
l so a thread needs to judge the lock to get the lock release lock, so it's been extended for a long time.
L Synchronous lock principle and toilet
Multiple threads accessing a shared data will set a sync lock
Synchronization methodL Code Concise
L Extract thread-sharing data and synchronization into a single method
The declaration of the L method plus the Sync keyword and then delete the sync no code block
L StringBuffer have this kind of synchronization method. Slow Running
L StringBuilder is a thread unsafe to run fast
Does the sync method have a lock?
L If the method is static
L RELEASE the sync lock, I can't see it.
L will not release if the code has an abnormal lock
L Therefore the lock interface appears after JDK1.5
L This interface provides a wide range of locking operations that can be obtained with more methods and statements than using synchornized
l Example
Lock get Lock
Unlock release lock
Reentrantlock
L Sync Lock and write a sync.
An infinite wait has occurred in the program
L Prerequisite must be multi-threaded synchronous nesting
L thread into sync get lock not out sync won't release lock
L First person needs a second person's lock. The second person has the lock that needs the first person
L
Simulation implementationL Define two lock objects a B
L loop with odd even to determine thread 1 and thread 2
L then a test class
L Program Run Results program will never stop running
L also called thread communication
L Multiple threads handle the same resource
• Each thread task is different
L If we want to use resources rationally
L need a means to enable each thread to effectively utilize resources
L This method is called the waiting wake mechanism.
L For example, before the ticket sales, there are now threads that need extra tickets.
ExampleL Resource Class
L Two thread class input and output
L Test Class
Because there are two of objects
L Resolve
L Resolve
A) Input class grabbed the CPU to assign a value to three men
b) The output of the assignment is not grabbed by the CPU
c) The input class still grabs the CPU to assign the value Lisi
D) The Lisi has not yet been assigned a value of NV
e) Output class The CPU resources are directly output Lisi NV
f) There is a gender mess at this point
A) There is only one way to add a synchronous lock
b) Find shared data
c) lock in the input class
Output class Join Lock
It's still not solved.
L Resolve
A) Two threads are not the same lock
L final target one input one output alternately appears
The thread will only execute the Run method without assigning values and values
L The ideal state should be one-time assignment printing
L The next assignment only starts after the last assignment output
L must wait for the next input to finish before outputting
L Implementation Steps
L Get CPU execution first to ensure program execution input
L Add a variable to the resource class, Boolean flag
L Flage Assignment Complete for true description
L Flage for false instructions get value complete
L input needs to determine if the tag flage is true
If it is true, wait.
If False, assign the value and change the token to False
L output is also true
l Example
Input
Output
The result throws an exception
Abnormal
That means the wake-up and wait method callers are wrong.
Should be a lock object call
Modify
L Results
The Java self-study road-DAY17
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