U.S. stocks closed mixed on Friday, after Federal Reserve Vice Chairman Stanley Fischer raised the possibility of an interest rate hike in September. Fed Chair Janet Yellen made the case for another rate hike earlier in the session. Crude oil ended slightly higher after U.S. oil rig activity remained flat in the past week, snapping an eight-week streak of increases. Signs of growing domestic inventories have recently pressured crude prices. Blackberry (BBRY) briefly halted trading this afternoon to detail plans to redeem existing convertible debt and issue new debentures. CEO John Chen said restructuring of convertible debt will reduce interest expenses. Finally, Alibaba (BABA - Get Report) rose after MKM Partners increased its price target and reiterated a BUY rating. Analysts increased their value estimates for Alibaba's cloud and commerce businesses. TheStreet's Scott Gamm reports from Wall Street.