Synchronization control between tasks

Synchronization control between tasks

1. vxWorks Semaphores provide inter task communication 、 Sync 、 And mutually exclusive optimal choice
   1.1 Synchronization refers to the coordination of multiple tasks in the execution order , Make sure it doesn't
   Now there are errors related to time , In this case, the semaphore represents the waiting event , Initially, semaphores are not available , A task or interrupt handler releases the semaphore to notify the occurrence of this event , Once unblocked , The task executes the corresponding event to handle the program , It should be noted that the state of the semaphore used for synchronization should initially be empty , A task first waits for the semaphore released by other tasks .

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 The execution sequence between tasks is described as follows ：
ＳＥＭ＿ＩＤ　ｓｅｍＳｙｎｃ;
ｓｅｍＥｒｒｏｒＳｙｎｃ＝ｓｅｍＢＣｒｅａｔｅ（ＳＥＭ＿Ｑ＿ＦＩＦＯ,ＳＥＭ＿
ＥＭＰＴＹ）;／＊ Create a semaphore that displays alarm information ＊／
ｓｅｍＮｅｗＥｒｒｏｒＳｙｎｃ＝ｓｅｍＢＣｒｅａｔｅ（ＳＥＭ ＿Ｑ＿ＦＩＦＯ,
ＳＥＭ＿ＥＭＰＴＹ）;／＊ Create a semaphore that displays new alarm information ＊／
ｔａｓｋＥｒｒｏｒＣｈｅｃｋ（ｖｏｉｄ）｛
···／＊ First display the error message ＊／
ｓｅｍＧｉｖｅ（ｓｅｍＥｒｒｏｒＳｙｎｃ）;
ｓｅｍＧｉｖｅ（ｓｅｍＮｅｗＥｒｒｏｒＳｙｎｃ）;
｝
｝

`ｔａｓｋＥｒｒｏｒＤｉｓｐＣｉｒｃｌｅ（ｖｏｉｄ）｛
`ｓｅｍＴａｋｅ（ｓｅｍＥｒｒｏｒＳｙｎｃ,ＷＡＩＴ＿ＦＯＲＥＶＥＲ）;
ｓｅｍＴａｋｅ（ｓｅｍＮｅｗＥｒｒｏｒＳｙｎｃ,ＷＡＩＴ＿ＦＯＲＥＶＥＲ）;
···;／＊ Cycle the display of alarm information ＊／
｝

  because ｓｅｍＥｒｒｏｒＳｙｎｃ and ｓｅｍＮｅｗＥｒｒｏｒＳｙｎｃ Of   first   beginning   value   Unavailable , If the task ｔａｓｋＥｒｒｏｒＤｉｓｐＣｉｒｃｌｅ（） First execution will inevitably block , Only in the task ｔａｓｋＥｒｒｏｒＣｈｅｃｋ（） After execution ｓｅｍＧｉｖｅ（） After the operation , send ２ After semaphores are available , Mission ｔａｓｋＥｒｒｏｒＤｉｓｐＣｉｒｃｌｅ（） To execute .


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