Re: is +=1 thread safe

Gary Herron <[EMAIL PROTECTED]> writes: > The test was meant to simulate the OP's problem, but even with your suggestion > of using numpy, it *still* fails! Well, although I haven't tested it extensively, it doesn't appear to fail for me, with numpy 1.02 and an AMD Athlon(tm) XP 2800+ under lin

Re: is +=1 thread safe

In article <[EMAIL PROTECTED]>, Gary Herron <[EMAIL PROTECTED]> wrote: > >However, the upshot of all of this is that one must maintain extreme >skepticism. Unless you know both your Python code and any extension >modules you call, and you know them at a level necessary to find such >details,

Re: is +=1 thread safe

Carl Banks wrote: On May 4, 12:03 pm, Gary Herron <[EMAIL PROTECTED]> wrote: Alexander Schmolck wrote: Gary Herron <[EMAIL PROTECTED]> writes: But... It's not! A simple test shows that. I've attached a tiny test program that shows this extremely clearly. Please run

Re: is +=1 thread safe

On May 4, 2:13 pm, Carl Banks <[EMAIL PROTECTED]> wrote: > However, what I said was not wholly untrue: code in C extensions is > protected by the GIL and thus not interruptable, unless it either > releases the GIL, or calls back into Python code (which is apparently > what numpy scalars do). And,

Re: is +=1 thread safe

On May 4, 12:03 pm, Gary Herron <[EMAIL PROTECTED]> wrote: > Alexander Schmolck wrote: > > Gary Herron <[EMAIL PROTECTED]> writes: > > >> But... It's not! > > >> A simple test shows that. I've attached a tiny test program that shows > >> this > >> extremely clearly. Please run it and watch it f

Re: is +=1 thread safe

Alexander Schmolck <[EMAIL PROTECTED]> wrote: > Gary Herron <[EMAIL PROTECTED]> writes: > >> But... It's not! >> >> A simple test shows that. I've attached a tiny test program that >> shows this extremely clearly. Please run it and watch it fail. > > In [7]: run ~/tmp/t.py > final count: 200

Re: is +=1 thread safe

Alexander Schmolck wrote: Gary Herron <[EMAIL PROTECTED]> writes: But... It's not! A simple test shows that. I've attached a tiny test program that shows this extremely clearly. Please run it and watch it fail. In [7]: run ~/tmp/t.py final count: 200 should be: 200 (I

Re: is +=1 thread safe

Gary Herron <[EMAIL PROTECTED]> writes: > But... It's not! > > A simple test shows that. I've attached a tiny test program that shows this > extremely clearly. Please run it and watch it fail. In [7]: run ~/tmp/t.py final count: 200 should be: 200 (I took the liberty to correct yo

Re: is +=1 thread safe

Gary Herron wrote: > No NO NO! The only way to increment a variable in memory is > through a three step process: > > Load a register from a memory location > Increment the register > Store the value back into memory. I suggest you read "Intel 64 and IA-32 Architectures Software Developer

Re: is +=1 thread safe

Carl Banks wrote: On May 3, 7:44 pm, Gary Herron <[EMAIL PROTECTED]> wrote: Alexander Schmolck wrote: AlFire <[EMAIL PROTECTED]> writes: The threading module already has a function to return the number of Thread objects currently alive. I have threads within threads

Re: is +=1 thread safe

On May 3, 7:44 pm, Gary Herron <[EMAIL PROTECTED]> wrote: > Alexander Schmolck wrote: > > AlFire <[EMAIL PROTECTED]> writes: > > >>> The threading module already has a function to return the number of Thread > >>> objects currently alive. > > >> I have threads within threads - so it does not suit m

Re: is +=1 thread safe

Alexander Schmolck wrote: AlFire <[EMAIL PROTECTED]> writes: The threading module already has a function to return the number of Thread objects currently alive. I have threads within threads - so it does not suit me :-(. How about using a scalar numpy array? They are mutable,

Re: is +=1 thread safe

Alexander Schmolck wrote: AlFire <[EMAIL PROTECTED]> writes: The threading module already has a function to return the number of Thread objects currently alive. I have threads within threads - so it does not suit me :-(. How about using a scalar numpy array? They are mutable, so I assume tha

Re: is +=1 thread safe

AlFire <[EMAIL PROTECTED]> writes: >> The threading module already has a function to return the number of Thread >> objects currently alive. > > I have threads within threads - so it does not suit me :-(. How about using a scalar numpy array? They are mutable, so I assume that x += 1 should be at

Re: is +=1 thread safe

Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> writes: > On Fri, 02 May 2008 19:23:54 +0100, Arnaud Delobelle wrote: > >> Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> writes: >> >>> >>> There are no modern processors with an opcode for incrementing a memory >>> location!? At least my C64 can do th

Re: is +=1 thread safe

On Fri, 02 May 2008 19:23:54 +0100, Arnaud Delobelle wrote: > Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> writes: > >> >> There are no modern processors with an opcode for incrementing a memory >> location!? At least my C64 can do that. ;-) > > Indeed! I remember a simple use was to make the

Re: is +=1 thread safe

Duncan Booth wrote: [...] is equivalent to: x = x.__iadd__(1) thx all for answers and hints ... Generating hundreds of threads is, BTW, a very good way to get poor performance on any system. Don't do that. Create a few threads and put the actions for those threads into a Queue. If

Re: is +=1 thread safe

Hrvoje Niksic <[EMAIL PROTECTED]> writes: > Since the += operator is not compiled into a single bytecode > instruction, it needs the lock. Aha, you are right. What I was remembering is that xrange.next is atomic in CPython, i.e. you can say something like counter = xrange(1) and the

Re: is +=1 thread safe

Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> writes: > > There are no modern processors with an opcode for incrementing a memory > location!? At least my C64 can do that. ;-) Indeed! I remember a simple use was to make the border change colour very fast, a v. cool effect when you're 12!

Re: is +=1 thread safe

Duncan Booth schrieb: Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote: On Thu, 01 May 2008 15:33:09 -0700, Gary Herron wrote: Of course it's not thread safe. For the same reason and more basic, even the expression i++ is not thread safe in C++. Any such calculation, on modern processor

Re: is +=1 thread safe

Paul Rubin writes: > AlFire <[EMAIL PROTECTED]> writes: >> But I still can not believe that +=1 is not a thread safe operation. > > In CPython I believe it is thread safe, because of the global > interpreter lock. Thread switches can happen only between bytecode > execu

Re: is +=1 thread safe

Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote: > On Thu, 01 May 2008 15:33:09 -0700, Gary Herron wrote: > >> Of course it's not thread safe. For the same reason and more basic, >> even the expression i++ is not thread safe in C++. >> >> Any such calculation, on modern processors, require

Re: is +=1 thread safe

AlFire <[EMAIL PROTECTED]> writes: > But I still can not believe that +=1 is not a thread safe operation. In CPython I believe it is thread safe, because of the global interpreter lock. Thread switches can happen only between bytecode executions, not in the middle of a bytecode, even though execu

Re: is +=1 thread safe

On Thu, 01 May 2008 15:33:09 -0700, Gary Herron wrote: > Of course it's not thread safe. For the same reason and more basic, > even the expression i++ is not thread safe in C++. > > Any such calculation, on modern processors, requires three operations: > retrieve value of i into a register,

Re: is +=1 thread safe

AlFire wrote: Hi, I have a piece of software which uses threads in very massive way - like hundreds of them generated every second. there is also a piece of code which maintains the number of outstanding threads, simply counter+=1 is executed when before starting the thread and counter-=1

Re: is +=1 thread safe

AlFire wrote: Hi, all is very simple and by the end of the program life I expect the counter to zero out. however I am getting values -1, -2, 1 ,2 ,3 and quite often 0 as expected. I guarded those statement with Lock.{acquire,release} and now it always returns 0. But I still can not belie

Re: is +=1 thread safe

AlFire schrieb: Hi, I have a piece of software which uses threads in very massive way - like hundreds of them generated every second. there is also a piece of code which maintains the number of outstanding threads, simply counter+=1 is executed when before starting the thread and counter-

Re: is +=1 thread safe

AlFire <[EMAIL PROTECTED]> wrote: > But I still can not believe that +=1 is not a thread safe operation. > > > Any clue? The statement: x+=1 is equivalent to: x = x.__iadd__(1) i.e. a function call followed by an assignment. If the object is mutable then this *may* be safe so

Re: is +=1 thread safe

If no other threads will be accessing the counter, there will be no problem. -- http://mail.python.org/mailman/listinfo/python-list