OSF DCE Application Development Guide--Introduction and Style Guide

OSF DCE Application Development Guide—Introduction and Style Guide
TABLE 2-1. Thread-Safe Calls
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_sleep( ) accept( ) atfork( ) calloc( )
catclose( ) catgets() catopen() cfree( )
close( ) connect( ) creat( ) ctermid( )
cuserid( ) dup( ) dup2( ) fclose()
fcntl() fdopen( ) fflush() fgetc( )
fgets( ) fopen() fork() fprintf( )
fputc( ) fputs( ) fread( ) free()
freopen( ) fscanf() fseek( ) ftell( )
fwrite( ) getc( ) getchar( ) gets( )
getw( ) isatty( ) malloc( ) mktemp( )
open() pclose( ) pipe() popen()
printf( ) putc() putchar( ) puts()
putw() read() readv( ) realloc( )
recv() recvfrom() recvmsg( ) rewind()
scanf( ) select() send() sendmsg( )
sendto( ) setbuf( ) setbuffer( ) setlinebuf( )
setvbuf( ) sigaction( ) sigwait( ) sleep()
socket( ) socketpair() sprintf( ) sscanf()
system( ) tempnam() tmpfile( ) tmpnam()
ttyname( ) ttyslot() vfprintf( ) vprintf()
vsprintf( ) write( ) writev()
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What follows is a summary of the thread-safety rules that should be followed when using
the pthread facilities. The list is by no means comprehensive; it describes the places
where multithreaded applications most frequently go wrong.
• Access to all shared objects should be protected by the appropriate synchronization
mechnisms. The pthread global lock is not appropriate for such synchronization.
• Mutexes should be used only to protect resources held for a short period of time. In
particular, note that pthread_mutex_lock( ) is not a cancellation point. Resources
needing to be held exclusively for a long time should be protected by condition
variables rather than mutexes, as this will not inhibit cancelability (see Section
2.3.3.2).
• A shared object should be protected by only one mutex.
• Be sure to use the available thread-safe library calls. These may be available as
wrapped routines, via the pthread.h header file, or your implementation may supply
reentrant libraries which must be linked with DCE applications.
• Avoid nonwrapped process-blocking system calls, such as wait( ).
• When threads need to acquire more than one mutex at a time, create a locking
sequence and require that all threads follow the sequence.
• Do not make any assumptions about the atomicity of operations, as these are unlikely
to be portable.
• In general, to avoid priority inversion, when three or more threads of different
priorities access a lock, associate a priority with the lock and force any thread to raise
its priority to the lock priority before acquiring the lock. Note that the default
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