faq.so

berkeley db 4.6.21的源码。berkeley db是一个简单的数据库管理系统

m4_comment([$Id: faq.so,v 10.3 2002/12/10 23:41:42 mjc Exp $])

m4_ref_title(Programmer Notes,
    Programmer notes FAQ,, program/runtime, lock/intro)

m4_nlistbegin

m4_idefz(task/thread @priority)
m4_nlist([dnl
m4_bold([What priorities should threads/tasks executing m4_db functions
be given?])

m4_p([dnl
Tasks executing m4_db functions should have the same, or roughly
equivalent, system priorities.  For example, it can be dangerous to give
tasks of control performing checkpoints a lower priority than tasks of
control doing database lookups, and starvation can sometimes result.])])

m4_nlist([dnl
m4_bold([Why isn't the C++ API exception safe?])

m4_p([dnl
The m4_db C++ API is a thin wrapper around the C API that maps most
return values to exceptions, and gives the C++ handles the same
lifecycles as their C counterparts.  One consequence is that if an
exception occurs while a cursor or transaction handle is open, the
application must explicitly close the cursor or abort the transaction.])

m4_p([dnl
Applications can be simplified and bugs avoided by creating wrapper
classes around m4_ref(Dbc) and m4_ref(DbTxn) that call the appropriate
cleanup method in the wrapper's destructor.  By creating an instance
of the wrappers on the stack, C++ scoping rules will ensure that the
destructor is called before exception handling unrolls the block that
contains the wrapper object.])])

m4_nlistend

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