text/template: fix race condition on function maps
The Template objects are supposed to be goroutine-safe once they
have been parsed. This includes the text and html ones.
For html/template, the escape mechanism is triggered at execution
time. It may alter the internal structures of the template, so
a mutex protects them against concurrent accesses.
The text/template package is free of any synchronization primitive.
A race condition may occur when nested templates are escaped:
the escape algorithm alters the function maps of the associated
text templates, while a concurrent template execution may access
the function maps in read mode.
The less invasive fix I have found is to introduce a RWMutex in
text/template to protect the function maps. This is unfortunate
but it should be effective.
Fixes #9945
Change-Id: I1edb73c0ed0f1fcddd2f1516230b548b92ab1269
Reviewed-on: https://go-review.googlesource.com/10101 Reviewed-by: Rob Pike <r@golang.org>