Background: The backend python (Updating ...)
A. Inter-process communication
Five kinds :
1. Pipeline
2. Named Pipes
3. Shared Memory
4. semaphore
The message queue
Second, the difference between processes and threads :
1. The process is the basic unit of the operating system resource allocation, and the thread is the basic unit of task scheduling and execution of
2. Memory allocation system allocates memory for each process , and is shared between threads of memory
3 .Costs for each process has its own memory space,large overhead when switching between processes,threads share memory
4. The process contains no thread relationship can be seen as a single thread , if there are multiple threads , then the process a number of lines execution , the thread is part of the process
Three deadlock condition :
1. mutually exclusive conditions resources can not be shared processes
2. The request has been keeping conditions resources processes can apply for a new resource again
3. Non-deprivation already allocated resources can not be forcibly deprived
4. A circular wait condition system composed of a number of process loop , the loop every process in an adjacent process is waiting for a resource occupied
Four deadlock prevention :
Failure condition
Five .python garbage collection
Reference count-based recovery generational supplemented space for time
Reference count : when the referenced object is created or passed as a parameter to be passed or vessel , reference count by one
When the object is explicitly destroyed (del) reference count by one is destroyed or be given a new name of the object reference or an object or objects out of scope of the element from the container or containers
Generational Recovery : The memory is divided into three generations , 012 corresponding to the three lists , their survival over time the frequency of garbage collection object increases decreases , the newly created object will be allocated in the young generation , when the young generation of the list the total number reaches the upper limit , python garbage collection mechanism is triggered , the recovery of lost objects can be recycled , can not object to the recovery in years , and so on
VI. Four waving three-way handshake
VII. Www.baidu.com in the address bar to the page showing what happened
other.
session and cookie and Differences
nginx proxy_pass Configuration