A Phase III, Randomized, Double-Blind Controlled Trial for Evaluating Jaktinib vs. Hydroxycarbamide in Subjects with Primary Myelofibrosis (PMF) or Post-Polycythemia Vera or Post-Essential Thrombocythemia Myelofibrosis

INTERVENTION: 1:Jaktinib hydrochloride tablets,100mg bid;2:Hydroxycarbamide tablets 0.5g bid; CONDITION: Primary Myelofibrosis (PMF) or Post‐polycythemia Vera or Post‐ essential Thrombocythemia Myelofibrosis (Post‐PV/ET MF) PRIMARY OUTCOME: Spleen Volume Response rate at Week 24; SECONDARY OUTCOME: Objective Response Rate (complete remission + partial remission);Spleen Response;Anemia Response;Response rate of MF‐related symptoms; INCLUSION CRITERIA: 1. Aged >=18 years old male or female; 2. Subjects diagnosed with a PMF according to World Health Organization criteria (2016 Edition), or patients diagnosed with a Post‐PV‐MF or Post‐EF‐MF according to International Working Group for Myeloproliferative Neoplasms Research and Treatment criteria; 3. High risk or intermediate‐2 risk as defined by the Dynamic International Prognostic Scoring System (DIPSS) for Primary Myelofibrosis; 4. Subjects have no plan for stem cell transplantation in the near future; 5. Life expectancy of > 24 weeks; 6. ECOG performance status of 0‐1; 7. Palpable splenomegaly at least 5 cm below left costal margin; 8. Peripheral blood blast count <=10%; 9. Subjects who have not yet received treatment with a JAK inhibitor, or Subjects who have been treated with JAK inhibitors for <=10 days; 10. Subjects have not received growth factor, thrombopoietin mimetics or platelet transfusion(s) within 2 weeks before the