# db_env_set_func_yield

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    #include <db.h>

    int
    db_env_set_func_yield(int (*func_yield)(void));

# Description

The Berkeley DB library requires the ability to yield the processor from the current thread of control to any other waiting threads of control. The func_yield argument must conform to the following interface:

>     int yield(void);

The func_yield function must be able to cause the rescheduling of all participants in the current Berkeley DB environment, whether threaded or not. It may be incorrect to supply a thread yield function if more than a single process is operating in the Berkeley DB environment. This is because many thread-yield functions will not allow other processes to run, and the contested lock may be held by another process, not by another thread.

If no func_yield function is specified, or if the yield function returns an error, the function specified by the db_env_set_func_sleep entry will be used instead or subsequently; that is, if no yield function is specified, or if it is possible for the yield function to fail, the sleep function must cause the processor to reschedule any waiting threads of control for execution.

The func_yield function must return the value of errno on failure and 0 on success.

The db_env_set_func_yield interface affects the entire application, not a single database or database environment.

Although the db_env_set_func_yield interface may be used to configure Berkeley DB at any time during the life of the application, it should normally be called before making any calls to the db_env_create or db_create functions.

The db_env_set_func_yield function returns a non-zero error value on failure and 0 on success.

# Errors

The db_env_set_func_yield function may fail and return a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

The db_env_set_func_yield function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the db_env_set_func_yield function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

db_env_set_func_close, db_env_set_func_dirfree, db_env_set_func_dirlist, db_env_set_func_exists, db_env_set_func_free, db_env_set_func_fsync, db_env_set_func_ioinfo, db_env_set_func_malloc, db_env_set_func_map, db_env_set_func_open, db_env_set_func_read, db_env_set_func_realloc, db_env_set_func_seek, db_env_set_func_sleep, db_env_set_func_unlink, db_env_set_func_unmap, db_env_set_func_write, and db_env_set_func_yield.`

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