Does Java share global variables among multiple processes?

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Preface

Question: is global variable sharing among multiple processes?

Import multiprocessing as mul_p

Import time

Egg1 = 1

Def write (egg2, Q):

Global egg1

Print ("write Global variable Egg [% s]..."% egg1)

Print ("write Egg [% s]..."% egg2)

Egg1-= 1

Print ("write Global variable Egg [% s]... original Egg [1]"% egg1)

# put the value of the modified egg 1 into the queue

Q.put (egg1)

Def read (egg2, Q):

Global egg1

Print ("read Global variable Egg [% s]..."% egg1)

Print ("read Egg [% s]..."% egg2)

While True:

# extract the value of the global variable Egg 1 in the p1 child process from the queue

Egg1 = q.get ()

Print ("value of global variable egg [1] in write received by read:% d"% egg1)

If q.empty ():

Print ("received...")

Break

Def main ():

# suppose even a process needs to print the following egg 2

Egg2 = 2

# ① create a queue. If you don't need to fill it, the queue can be very large, but there is a limit. Let's not consider it.

# if the number is x, the queue can store x data

Q = mul_p.Queue ()

# ② creates two process objects

P1 = mul_p.Process (target=write, args= (egg2, Q,))

P2 = mul_p.Process (target=read, args= (egg2, Q,))

# ③ makes the two child processes work

P1.start ()

# Let the main process rest for 1 second and let the p1 child process finish first, otherwise the two child processes will scramble to execute the printout.

Time.sleep (1)

P2.start ()

If _ name__ = = "_ _ main__":

Main ()

Running result: write global variable color egg [1].

Write eggs [2].

Write global variable color egg [0]. The original egg [1]

Read global variable color egg [1].

Read eggs [2].

The value of the global variable color egg [1] received by read in write: 0

Reception complete. II. Summary

The values of global variables between ① processes are not shared.

Of

Processes: this is because each process created will copy a copy of the original code (global variable or initial value) for its own use, so the code between processes is the same, but the variables and data are independent.

② processes can pass variables, lists, and string values (including global variable values) through queues created by Queue.

③ parameters in each process task, except global variables (function local variables), the rest of the parameters need to be passed into the internal parameters through external arguments. Queue Q of the previous routine, in particular, should be passed to two processes as arguments, so that communication between the two processes can be realized.

The relationship and difference between ③ process and thread: ① process contains multiple threads ② inter-process does not share variables and resources; shared variables and resources between threads ③ use time.sleep (), you can stop the current process and let other processes start working

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