server: refactor subproc handling (#28555)

* server: refactor subproc handling

* fix Windows build

* download: keep concurrent downloads of one blob apart

Every process writes the same path + .downloadInProgress, so a second
download of the same blob finds that file, takes it for its own partial
transfer and asks for the bytes after it, which produces a corrupt
result. The in-progress file now carries the pid of the process writing
it.

std::rename also replaces an existing destination on POSIX but fails on
Windows, so a download whose blob appeared in the meantime is dropped
after every retry and an etag rewrite silently keeps the old value.
std::filesystem::rename has the POSIX behaviour everywhere, and the
error now carries the reason reported by the system.

* Revert "download: keep concurrent downloads of one blob apart"

This reverts commit 917b83f149.

* tests: serialize the router tests that download the same model

Parallel workers share one cache, so the two tests fetch the same blob
into the same in-progress file and race to rename it. They now take a
file lock around the download, like the session fixture does for the
preset models.

* Revert "tests: serialize the router tests that download the same model"

This reverts commit c368a4a98c.

---------

Co-authored-by: Pascal <admin@serveurperso.com>

tools/server/server-common.cpp

@@ -16,6 +16,21 @@
 #include <cstring>
 #include <type_traits>
 
+#ifdef _WIN32
+// windows.h defines min and max as macros, which breaks std::min and std::max
+#define WIN32_LEAN_AND_MEAN
+#ifndef NOMINMAX
+#   define NOMINMAX
+#endif
+#include <windows.h>
+#include <io.h>
+#else
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <unistd.h>
+#endif
+
 json format_error_response(const std::string & message, const enum error_type type) {
     std::string type_str;
     int code = 500;
@@ -1832,3 +1847,133 @@ server_tokens format_prompt_rerank(
 
     return result;
 }
+
+//
+// server_subproc
+//
+
+bool server_subproc::has_output() {
+    if (out_handle >= 0) {
+        return true;
+    }
+    FILE * f = sproc.stdout_file(); // combined stdout/stderr
+    if (!f) {
+        return false;
+    }
+#ifdef _WIN32
+    HANDLE h = (HANDLE) _get_osfhandle(_fileno(f));
+    if (h != INVALID_HANDLE_VALUE) {
+        out_handle = (intptr_t) h;
+    }
+#else
+    int fd = fileno(f);
+    if (fd >= 0) {
+        fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);
+        out_handle = fd;
+    }
+#endif
+    return out_handle >= 0;
+}
+
+int server_subproc::read_output(char * buf, size_t len) {
+    if (!has_output()) {
+        return -1;
+    }
+#ifdef _WIN32
+    HANDLE h     = (HANDLE) out_handle;
+    DWORD  avail = 0;
+    if (!PeekNamedPipe(h, NULL, 0, NULL, &avail, NULL)) {
+        return -1; // pipe broken, child gone
+    }
+    if (avail == 0) {
+        return 0;
+    }
+    DWORD to_read = avail < (DWORD) len ? avail : (DWORD) len;
+    DWORD got     = 0;
+    if (!ReadFile(h, buf, to_read, &got, NULL) || got == 0) {
+        return -1;
+    }
+    return (int) got;
+#else
+    while (true) {
+        ssize_t r = read((int) out_handle, buf, len);
+        if (r > 0) {
+            return (int) r;
+        }
+        if (r == 0) {
+            return -1; // EOF
+        }
+        if (errno == EINTR) {
+            continue;
+        }
+        if (errno == EAGAIN || errno == EWOULDBLOCK) {
+            return 0;
+        }
+        return -1;
+    }
+#endif
+}
+
+server_subproc::waiter::waiter() {
+#ifndef _WIN32
+    int fds[2];
+    GGML_ASSERT(pipe(fds) == 0);
+    for (int fd : fds) {
+        fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);
+    }
+    wake_fd[0] = fds[0];
+    wake_fd[1] = fds[1];
+#endif
+}
+
+server_subproc::waiter::~waiter() {
+#ifndef _WIN32
+    close((int) wake_fd[0]);
+    close((int) wake_fd[1]);
+#endif
+}
+
+void server_subproc::waiter::wake() {
+#ifndef _WIN32
+    char c = 1;
+    (void) !write((int) wake_fd[1], &c, 1);
+#endif
+}
+
+void server_subproc::waiter::wait(const std::vector<server_subproc *> & procs, std::vector<bool> & ready, int64_t timeout_ms) {
+    ready.assign(procs.size(), false);
+#ifdef _WIN32
+    // no waitable wait exists for anonymous pipes, so poll them in 50 ms steps
+    bool any = false;
+    for (size_t i = 0; i < procs.size(); i++) {
+        DWORD avail = 0;
+        if (!procs[i]->has_output() || !PeekNamedPipe((HANDLE) procs[i]->out_handle, NULL, 0, NULL, &avail, NULL) || avail > 0) {
+            ready[i] = true; // data or broken pipe, read_output() tells which
+            any = true;
+        }
+    }
+    if (!any) {
+        int64_t step = timeout_ms < 0 ? 50 : std::min<int64_t>(timeout_ms, 50);
+        std::this_thread::sleep_for(std::chrono::milliseconds(step));
+    }
+#else
+    std::vector<pollfd> pfds;
+    pfds.reserve(procs.size() + 1);
+    pfds.push_back({ (int) wake_fd[0], POLLIN, 0 });
+    for (auto * p : procs) {
+        pfds.push_back({ p->has_output() ? (int) p->out_handle : -1, POLLIN, 0 }); // poll() skips negative fds
+    }
+    int timeout = timeout_ms < 0 ? -1 : (int) std::min<int64_t>(timeout_ms, std::numeric_limits<int>::max());
+    int r = poll(pfds.data(), pfds.size(), timeout);
+    if (r < 0 && errno != EINTR) {
+        LOG_ERR("%s: poll() failed: %s\n", __func__, strerror(errno));
+    }
+    if (pfds[0].revents) {
+        char buf[64];
+        while (read((int) wake_fd[0], buf, sizeof(buf)) > 0) {}
+    }
+    for (size_t i = 0; i < procs.size(); i++) {
+        ready[i] = pfds[i + 1].fd < 0 || pfds[i + 1].revents != 0;
+    }
+#endif
+}