In a sawtooth generator(circuit below) , the capacitor charges then when the thyristor turns on due to the bias voltage of R2 and R3, capacitor discharges to the thyristor like a short. Then after discharging the capacitor, the thyristor turns off and the capacitor charges again. This will form a sawtooth generator.
This current from R1 is approximately 100V/1kohm=100mA. Even if capacitor is fully discharged, this 100mA is enough to prevent the thyristor from turning off.
Since the thyristor act like a short(with small forward voltage), I thought current from R1 will short through thyristor thus the thyristor will never reach its holding current and will forever be on regardless how small the charge from the capacitor is.