pyserial - 可以从线程a写入串口，从线程b做阻塞读取吗？

Question

I tried googling this, couldn't find an answer, searched here, couldn't find an answer. Has anyone looked into whether it's thread safe to write to a Serial() object (pyserial) from thread a and do blocking reads from thread b?

I know how to use thread synchronization primitives and thread-safe data structures, and in fact my current form of this program has a thread dedicated to reading/writing on the serial port and I use thread-safe data structures to coordinate activities in the app.

My app would benefit greatly if I could write to the serial port from the main thread (and never read from it), and read from the serial port using blocking reads in the second thread (and never write to it). If someone really wants me to go into why this would benefit the app I can add my reasons. In my mind there would be just one instance of Serial() and even while thread B sits in a blocking read on the Serial object, thread A would be safe to use write methods on the Serial object.

Anyone know whether the Serial class can be used this way?

EDIT: It occurs to me that the answer may be platform-dependent. If you have any experience with a platform like this, it'd be good to know which platform you were working on.

EDIT: There's only been one response but if anyone else has tried this, please leave a response with your experience.

Answer 1

I have done this with pyserial. Reading from one thread and writing from another should not cause problems in general, since there isn't really any kind of resource arbitration problem. Serial ports are full duplex, so reading and writing can happen completely independently and at the same time.

Answer 2

我在Linux（和Windows）上以这种方式使用了pyserial，没问题！

Answer 3

I would recommend to modify Thread B from "blocking read" to "non blocking read/write". Thread B would become your serial port "Daemon".

Thread A could run at full speed for a friendly user interface or perform any real time operation.

Thread A would write a message to Thread B instead of trying to write directly to the serial port. If the size/frequency of the messages is low, a simple shared buffer for the message itself and a flag to indicate that a new message is present would work. If you need higher performance, you should use a stack. This is actually implemented simply using an array large enough to accumulate many message to be sent and two pointers. The write pointer is updated only by Thread A. The read pointer is updated only by Thread B.

Thread B would grab the message and sent it to the serial port. The serial port should use the timeout feature so that the read serial port function release the CPU, allowing you to poll the shared buffer and, if any new message is present, send it to the serial port. I would use a sleep at that point to limit the CPU time used by Thread B.. Then, you can make Thread B loop to the read serial port function. If the serial port timeout is not working right, like if the USB-RS232 cable get unplugged, the sleep function will make the difference between a good Python code versus the not so good one.

Answer 4

I wrote a script which is doing this. See: https://code.google.com/p/rpicopter/source/browse/RPiQuadroServer.py