我有一个需要包含不同事物之和的数组,因此我想对它的每个元素进行归约。
这是代码:
cdef int *a=<int *>malloc(sizeof(int) * 3)
for i in range(3):
a[i]=1*i
cdef int *b
for i in prange(1000,nogil=True,num_threads=10):
b=res() #res returns an array initialized to 1s
with gil: #if commented this line gives erroneous results
for k in range(3):
a[k]+=b[k]
for i in range(3):
print a[i]
直到有了gil,代码才能正常运行,否则给出错误的结果。
如何在不使用gil的情况下处理数组每个元素的减少导致gil我认为gil会阻塞其他线程
最佳答案
减少操作通常在实践中起作用的方法是分别为每个线程求和,然后在最后将它们相加。您可以使用类似的方法手动执行此操作
cdef int *b
cdef int *a_local # version of a that is duplicated by each thread
cdef int i,j,k
# set up as before
cdef int *a=<int *>malloc(sizeof(int) * 3)
for i in range(3):
a[i]=1*i
# multithreaded from here
with nogil, parallel(num_threads=10):
# setup and initialise a_local on each thread
a_local = <int*>malloc(sizeof(int)*3)
for k in range(3):
a_local[k] = 0
for i in prange(1000):
b=res() # Note - you never free b
# this is likely a memory leak....
for j in range(3):
a_local[j]+=b[j]
# finally at the end add them all together.
# this needs to be done `with gil:` to avoid race conditions
# but it isn't a problem
# because it's only a small amount of work being done
with gil:
for k in range(3):
a[k] += a_local[k]
free(a_local)
关于python - cython并行中数组的减少,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/36533455/