fig11

First thread gains ownership.

First thread gives up ownership to second thread.

Second thread tries to gain ownership, butis suspended.

Third thread tries to gain ownership, butis suspended.

_ Fourth thread tries to gain

ownership, butis suspended.

Second thread gives up ownership to third thread.

Third thread gives up ownership to fourth thread.

_ Fourth thread gives up

i    ownership. Critical

/    sectionno longer

/    owned.