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[OpenMP] Fix deadlock for detachable task with child tasks
This patch fixes https://bugs.llvm.org/show_bug.cgi?id=49066. For detachable tasks, the assumption breaks that the proxy task cannot have remaining child tasks when the proxy completes. In stead of increment/decrement the incomplete task count, a high-order bit is flipped to mark and wait for the incomplete proxy task. Differential Revision: https://reviews.llvm.org/D101082
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// RUN: %libomp-compile-and-run | ||
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// Checked gcc 10.1 still does not support detach clause on task construct. | ||
// UNSUPPORTED: gcc-4, gcc-5, gcc-6, gcc-7, gcc-8, gcc-9, gcc-10 | ||
// gcc 11 introduced detach clause, but gomp interface in libomp has no support | ||
// XFAIL: gcc-11, gcc-12 | ||
// clang supports detach clause since version 11. | ||
// UNSUPPORTED: clang-10, clang-9, clang-8, clang-7 | ||
// icc compiler does not support detach clause. | ||
// UNSUPPORTED: icc | ||
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// The outer detachable task creates multiple child tasks with dependencies | ||
// when the last inner task incremented ret, the task calls omp_fulfill_event | ||
// to release the outer task. | ||
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#include <omp.h> | ||
#include <stdio.h> | ||
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int *buf; | ||
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int foo(int n) | ||
{ | ||
int ret = 0; | ||
for (int i = 0; i < n; ++i) { | ||
omp_event_handle_t event; | ||
#pragma omp task detach(event) firstprivate(i,n) shared(ret) default(none) | ||
{ | ||
for (int j = 0; j < n; ++j) { | ||
#pragma omp task firstprivate(event,i,j,n) shared(ret) default(none) depend(out:ret) | ||
{ | ||
//printf("Task %i, %i: %i\n", i, j, omp_get_thread_num()); | ||
#pragma omp atomic | ||
ret++; | ||
#if _OPENMP | ||
if (j == n-1) { | ||
//printf("Task %i, %i: omp_fulfill_event()\n", i, j); | ||
omp_fulfill_event(event); | ||
} | ||
#endif | ||
} | ||
} | ||
} | ||
} | ||
// the taskwait only guarantees the outer tasks to complete. | ||
#pragma omp taskwait | ||
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return ret; | ||
} | ||
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int main() | ||
{ | ||
int ret; | ||
#pragma omp parallel | ||
#pragma omp master | ||
{ | ||
ret = foo(8); | ||
} | ||
printf("%i\n", ret); | ||
//CHECK: 64 | ||
return 0; | ||
} |